Complexity of implementing canine visceral leishmaniasis control measures at a population level: use of impregnated deltamethrin collars and culling

Complexity of implementing canine visceral leishmaniasis control measures at a population level: use of impregnated deltamethrin collars and culling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Complexity of implementing canine visceral leishmaniasis control measures at a population level: use of impregnated deltamethrin collars and culling José Flávio Vidal Coutinho, Dayse Caroline Severiano Cunha, Iraci Duarte Lima, and 15 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7427065/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background In Brazil, dogs are considered the main reservoir for Leishmania infantum , the main causative agent of visceral leishmaniasis (VL) for dogs and humans. The goal of this study was to evaluate the effectiveness of deltamethrin impregnated collars for controlling of canine L. infantum infection. Methods A prospective case-control intervention study was performed in paired neighborhoods, implementing deltamethrin-impregnated collars in one area and culling VL dogs in both. Four cross-sectional serosurvey of canine, and one of human L. infantum infections were performed. Sand flies were monitored along 19 months. Bayesian model and Moran’s index of canine L. infantum infection rates were used to detect spatial autocorrelation. Results A total of 11,285 dog evaluations were performed over 27 months. At baseline, rates of canine L. infantum infection differed between areas: 10% in the intervention and 19.7% in control area [odds ratio 0.454 (95% CI: 0.364, 0.566)]. Human L. infantum infection also varied, with rates of 4% and 14.3% in the intervention and control areas, respectively. Comparing dogs and humans L. infantum infections within each area, the OR of infection were 2.405 [95% CI: (1.720, 3.363) in the control area and 1.459 [(95% CI: 1.117, 1.906) in the intervention area. The pooled OR across both areas was 1.776 [95% CI: (1.441, 2.189)]. Large scale implementation of insecticide collars was effective at 6 months [ OR 0.448, 95% CI: (0.343, 0.584)], but the effect was not sustained thereafter. Nonetheless, dogs wearing collar had lower of L. infantum seroconversion (p = 0.044), and households with collared dogs had reduction in sand fly abundance. Collar coverage remained below 80%, and approximately 40% of collars were lost before the scheduled replacement at 6-month interval. Reduction in VL dog culling was observed in both areas at 6 and 12 months. Spatial analysis revealed outlier blocks of canine infection, forming clusters that influence infection dynamics in neighboring areas. Conclusions There was reduction in Leishmania seroconversion in dogs that used collars. The use of collars reduced sand fly density in the household. Culling of VL dogs were not systematic because of loss of follow up or non-consent from the owners. Canine visceral leishmaniasis Leishmania infantum collars impregnated deltamethrin Lutzomyia longipalpis spatial dynamics Figures Figure 1 Figure 2 Figure 3 Background Visceral leishmaniasis (VL) is a major a vector-borne disease that primarily affects populations living in socioeconomically vulnerable areas, particularly in tropical and subtropical areas of the world ( 1 , 2 ). Overlapping outbreaks of human and canine VL have been reported in Spain, France and Italy. This illness has a tremendous impact on the canine population in both Europe and Latin America ( 3 – 5 ). Mortality in untreated dogs is high; however, one study in France reported it to be approximately 30% when antimony was used alone, decreasing when combination therapy was used ( 6 ). For humans, 5% of the cases are fatal, even with treatment ( 7 ). Undernourishment and immunodeficiency increase the risk of VL in both humans and dogs ( 8 , 9 ). Human co-infection of HIV and Leishmania infantum was first described in Europe ( 10 , 11 ). Currently, it accounts for approximately 15% of VL cases in Brazil ( 12 – 14 ). These individuals more often relapse and they tend to have a greater mortality than uncomplicated VL ( 14 ). The introduction of anti-retroviral therapy has decreased the risk of symptomatic human VL (authors observation, Bezerra et all, under revision). In a parallel scenario, undernourished dogs or dogs co-infected with tick-borne pathogens are at increased risk for symptomatic canine VL ( 15 , 16 ). All Brazilian regions report autochthonous cases of both human and canine VL ( 17 , 18 ). The adaptability of Lutzomyia longipalpis , the main vector implicated in Leishmania infantum transmission in South America, to peridomestic areas, together with the presence of highly infected, sustains the endemicity of this pathogen in these areas. The majority of Leishmania spp. transmission is thought to be vector-borne. However, case reports of human VL in non-endemic areas have documented vertical transmission of L. infantum ( 19 , 20 ). In addition, over the past two decades, numerous studies have demonstrated that L. infantum can be transmitted vertically in dogs, even in regions where no competent sand fly vector is present ( 21 , 22 ). Typing of those Leishmania isolates showed that they were from western Europe ( 23 , 24 ). Dogs are the main urban reservoir of L. infantum in Brazil, and in newly endemic VL areas, canine VL often precedes human disease ( 25 , 26 ). França-Silva et al demonstrated that systematic euthanasia of L. infantum seropositive dogs can be effective for VL control for both humans and dogs, if routinely maintained ( 3 , 27 ). Nonetheless, dog culling because of VL remains controversial ( 27 – 31 ), and novel strategies are needed. When people are diagnosed with VL in Brazil, the Ministry of Health usually inspects their dwellings aiming to identify vector breeding sites, and searches for L. infantum infected dogs. However, there is usually a lag between the diagnosis of human VL and implementation of control measures; which may allow further parasite dissemination. Persistence of L. infantum in the vertebrate host, particularly in humans, has been documented, adding another layer of complexity for control measures. A study in Brazil reported VL occurring decades after individuals had left the endemic regions, leading the authors to consider L. infantum as an opportunistic pathogen ( 32 ). Supporting this report, a more recent study with United States Military personnel provided evidence of the potential lag between infection and VL development in humans ( 33 , 34 ). Controlled studies have unequivocally demonstrated the efficacy of these collars in repelling insect bites (> 90%) and in their insecticidal activity ( 35 , 36 ). Furthermore, several intervention studies with deltamethrin-impregnated collars, conducted in Europe and Brazil, have evaluated the blockade of L. infantum transmission in dogs at the population level, with variable effectiveness outcomes. These discrepancies may be attributed to eco-epidemiological differences, experimental design complexity, and operational challenges in strategy implementation and sustainability ( 37 – 39 ). However, due to the complexity of L. infantum transmission and the limitations of this control model when applied at the community level, the strategy still requires refinement and optimization. Given the importance of decreasing canine L. infantum infection, this study aimed to evaluate the effectiveness of 4% deltamethrin-impregnated collars on the incidence of L. infantum infection in dogs, while investigating their influence on the spatial dynamics of parasite transmission and their impact on the abundance and of the vector Lutzomyia longipalpis —the primary agent of zoonotic transmission. Methods 2.1. Study Areas : The study was conducted between 2014-2017 in the north district of Natal, state of Rio Grande do Norte, Brazil, which is endemic for human and canine VL (Figure 1). The city has a population of 877,739 people (IBGE, www.ibge.gov.br). About 37.8% (303.543 people) of the city population live in the north district. The two locations Boa Esperança (intervention) and Jardim Progresso (control), Figure 1, were chosen based on prior surveillance studies for canine L. infantum infection and reports of human VL (40); from herein on we will use the names of control (Jardim Progresso) and intervention (Boa Esperança) areas. The intervention area had a population of 16,444 inhabitants, residing in an area of 246 blocks, whereas the control area had an estimated population of 17,375 inhabitants spread over 247 blocks. The team members of the Zoonosis Surveillance Unit visited the household and aided with recruitment the dog population. Figure 2 shows the number of dogs recruited and loss to follow up, and the ones that were culled in both areas. 2.2. Study Design: A prospective non-randomized intervention study was performed between 2014-2017. All blocks from the intervention (n=246) and control areas (n=247) were visited (Table S1). Dogs belonging to consenting owners received polyvinylchloride (PVC) collars impregnated with 4% deltamethrin (40 mg/g concentration), (Scalibor® ProtectorBands, Intervet).Dogs of consenting owners in the control area were followed without collar application. L. infantum serological surveys were performed at the time of recruitment and 6, 12, and 27 months later. Collars were placed at the time of recruitment and replaced after 6 and 12 months. If authorized, by the dog’s owner, VL dogs, with compatible symptoms and with confirmatory serologic testing, were euthanized by a veterinarian from the Zoonosis Surveillance Unit of the Health Secretariat of Natal (Table S2). A cross-sectional study of L. infantum infection in humans residing the same house of the recruited dogs at the onset of the study was performed. Information on current and past medical history and vaccination coverage were collected. Blood was drawn and a physical examination was performed. 2.3. Leishmania infantum serological test : Animals were screened for L. infantum infection by using the Rapid Dual Path Platform Test (DPP®). Animals whose samples were positive in the screening test were tested using a confirmatory Enzyme Linked Immunosorbent Assay (ElE). Both tests were produced by the Bio-Manguinhos Laboratory (Rio de Janeiro, RJ, Brazil). 2.4. Sand fly monitoring: The intervention and control areas were monitored for sand flies for 19 months, between August 2014 and February 2016. Flies were captured using CDC light traps in the peridomicile region surrounding 10 properties selected among these with fruit trees, organic debris-trash presence and in proximity of human VL case diagnosed within the last 4 years. In the intervention area, traps were distributed in houses with collared dogs (n=5 houses) and without dogs (n=5 houses). Traps were placed at 5:00 p.m. and collected at 6:00 a.m. Sand flies were placed in tubes with 70% ethyl alcohol and species were identified using Galati's classification (41,42). The relative abundance of sand flies – defined as the total number of vectors captured monthly divided by the number of households surveyed – home infestation, defined as the percentage of properties with vectors relative to the total number of properties surveyed, and the relative abundance of male versus female Lu. longipalpis were determined. 2.5. Spatial base analysis used in data plotting: The maps of the Intervention Area and Control Area subdivisions were generated from the SHAPEs of the census tracts, (43).The free software QGIS multiplatform (version 2.18) was used to process the maps, which allowed the visualization, editing and analysis of georeferenced data. 2.6. Statistical analysis : Statistical comparisons between population characteristics were done by Chi Square test. L. infantum ELISA data were compared between populations as odds ratios, and or relative risk. The impact of collars on sand fly density were compared by linear or logistical regression. The relationship between L. infantum infections in dogs and humans within or between the areas were determined with a combination of odds ratios and the Mantel-Haenszel statistic. The dynamics of spatial autocorrelation of canine L. infantum infectionby block was performed using a Local Empirical Bayesian Estimator, consisting of the local infection rate weighted by the rates of neighboring blocks. For each map, its Moran Scatter Diagram was drawn, with two-dimensional scatterplot. Linear models were adjusted with the location dummy variable to evaluate the effect of the presence of collars impregnated with deltamethrin on sand flies assessing relative abundance and household infestation. The means of the monthly series of entomological indicators from the intervention and control areas were compared. The means were stratified considering whether the household had dogs with collars or not. The significance of the local differential effect was determined by Student's t test. Odds ratios (ORs) for L. infantum infection in humans and dogs were calculated with 95% confidence intervals. A weighting formula was used to compute the Common Odds Ratio (COR), combining data from both areas. Conditional independence between infection status and species was tested Mantel-Haenszel statistic, which adjusts for potential confounders and provides a chi-square and p-value to assess the significance of the findings. Statistical analyses and graphical representations were performed using R Studio version 1.1.383 and R-System version 3.4.1 software. 2.7. Ethical Considerations The protocol was reviewed and approved by the Federal University of Rio Grande do Norte Ethical Committee on human research (CAAE Platform 37529814.1.0000.5537). The protocol for the use of dogs in the research was reviewed and approved by the Research Committee Ethics in the Use of Animals-(CEUA 062/2014). All participants or the legal guardian received information on the research and those who consented were recruited. Only dogs that the owner consented were recruited into the study. Results 3.1. Human and canine Leishmania infantum infections at the onset of the study Canine L. infantum infections were initially screened by DPP, and positives were confirmed by EIE. Human L. infantum infection was assessed by an in-house ELISA using soluble leishmania antigens (SLA) from a local isolate. At the onset of the study, 2,873 dogs recruited, 1,271 and 1,602 from the intervention and control areas, respectively, (Fig. 2). Unexpectedly, household characteristics and dog care differed between the two localities (Table 1). Dogs from the intervention area had higher vaccination coverage, had better availability of food and fewer signs of VL (Table 1). Overall, 9.9% in the intervention area and 19.6% of the dogs from control areas tested positive for L. infantum infection by serology. The prevalence of L. infantum infection was higher in the control than in the intervention area, with an odds ratio 0.454 (95%, CI 0.364, 0.566), for dogs positive in the intervention area versus control area, indicating a greater risk of infection in the latter (Table 2). At the onset of the study, L. infantum seropositivity in people was 4.4% (51/1156) in the intervention area and 14.3% (80/557) in the control areas (Table 3). In the intervention area, the odds of L. infantum infection in dogs compared with humans was 2.4, whereas in the control area was 1.46. The common odds ratio (COR) across both areas was 1.78 (95%CI: 1.44–2.19), with the use of a Mantel-Haenszel statistic equaling to 27.53 (df = 1,p-value < 0.001). These findings provide evidence of the dependence between L. infantum human and canine L. infantum infections (Table 3). 3.2. Dynamics of canine L. infantum infection During the 27-month observation period, a total of 11,285 dog evaluations were performed, as shown in Fig. 2. The enrolled canine population at onset of the study was re-evaluated 6 and 12 months, coinciding with collars were replacement. At the 6-month mark, there was a 53.6% (632/1179) loss to follow up in the intervention area, and 62.5% (935/1,495) in the control area. During the same period, 742 new dogs were enrolled in the intervention area and 1,087 in the control area. Dogs were withdrawn from the study because of adverse reactions or owner's decision and other causes (Table S3 ). The prevalence of L. infantum infection at baseline was 6.3% in the intervention area and 13.1% in the control area ( p = 0.0156). However, at 12 months, no difference was observed, OR 0.970 [ 95% CI: (0.760 to 1.239)], between the groups (Table 2). At 27 months—approximately nine months after the expected duration of collar efficacy—the estimated OR was 1.048 (95% CI: 0.847 to 1.298), again demonstrating no significant difference in infection status between the intervention and control areas. These analyses incorporated both incident cases among dogs newly enrolled at 6, 12, and 27 months, as well as data from dogs followed longitudinally. Notably, the only time point at which a significant difference in infection status was observed between study arms was at 6 months (Table 2). Of the dogs initially enrolled, only 102 and 179, respectively, from the control and in the intervention areas were monitored at all four time points: baseline, and follow-ups at 6, 12 and 27 months), (Fig. 2). Notably, 40.6% of dogs (222 of 547) dogs followed over time had either lost their collars or had them removed by owners prior to the recommended 6-month interval for replacement interval. The primary causes for collar loss or removal included were adverse reactions, voluntary removal by the owners and incidents such as interactions with other dogs (Table S3 ). Seroconversion rates among dogs in the areas are shown in Table 4. Among the 432 dogs that were seronegative at baseline, in the control areas, 33 seroconverted at 6 months (7.6% conversion). In comparison, of the 454 seronegative dogs in the intervention area, 15 seroconverted (3.3%). The estimated relative risk of L. infantum seroconvertion infection was 0.4653 (95% CI: 0.2557, 0.8469, p-0.0101). This indicated that dogs wearing the insecticidal collars had approximately half the risk of becoming L. infantum infected when serological testing was used as a diagnostic tool. At 12-month follow-up, 29 of the 303 dogs in the control area seroconverted, corresponding to a seroconversion rate of 9.6% (Table 4). In comparison, 20 of 343 dogs in the intervention area seroconverted (5.8%). The relative risk (RR) of seroconversion in the intervention group compared to the control group was 0.6092 ( p = 0.0732), At 27 months of follow-up, a further reduction in the relative risk (RR) of seroconversion was observed between the intervention and control areas, with an RR of 0.3561 (p = 0.0418), despite more than one year having passed since the last collar replacement (Table 4). In the control area, 10.1% of the 99 dogs monitored seroconverted, compared to 4.2% (26 of 139) in the intervention area (Table 4). 3.3. Spatial dynamics of dog L. infantum infection in the intervention and control areas. To evaluate potential spatial clustering of L. infantum infection among dogs, we analyzed the distribution of cases at the block level within each neighborhood. Figure 3 presents maps identifying blocks containing seropositive dogs. Using empirical Bayesian estimation to calculate the number of cases per block, and Moran’s I statistic to assess spatial autocorrelation, the neighborhood averages are displayed on the y-axis. Block values are represented using color-coded boxplots: red squares indicate values between the median and the third quartile; green squares represent values between the third quartile and the upper whisker; and black squares denote outliers above this upper limit. The estimated correlation coefficients, representing deviations in case counts for each block relative to the mean of its immediate neighbors, are shown in Figs. 3a, 3b, and 3c for the control area, and Figs. 3d, 3e, and 3f for the intervention area. Corresponding scatter plots are displayed in Figs. 3g, 3h, and 3i for the control area, and Figs. 3j, 3k, and 3l for the intervention area. In the control area at baseline (time 0), blocks with a spatial index above 0.79 were classified as outliers, as illustrated in the Moran scatterplots (Fig. 3d). Blocks with high ordinate values indicated spatial clustering of infection, where adjacent blocks also exhibited high infection rates, whereas blocks with ordinate values near zero were spatially isolated in terms of infection. For instance, as shown in Fig. 3d, blocks 512, 514, and 518 were identified as outliers with neighboring blocks displaying high average incidence, indicating spatial autocorrelation. In contrast, blocks 586 and 612 were also outliers but had neighboring blocks with low average incidence, reflecting spatial independence. At baseline, 23 outlier blocks were identified in the control area, of which 18 (78.3%) exhibited spatial autocorrelation and 5 (21.7%) did not (Table S4 ). After 12 months, although the threshold infection rate defining outliers decreased to 0.37, the number of outlier blocks increased to 26, with 18 (69.2%) showing spatial autocorrelation and 8 (30.8%) remaining spatially independent. By 27 months, the threshold for outlier classification rose again to 0.41, and the number of outlier blocks increased further to 30, including 19 (63.3%) with spatial autocorrelation and 11 (36.7%) without evidence of spatial grouping (Table S4 ). Clusters might be more readily identifiable in regions with low case numbers, whereas areas with higher infection densities may approach saturation, potentially masking clustering patterns. At baseline, the intervention area exhibited outlier blocks with indices above 0.31, a threshold lower than that observed in the control area alone. Notably, a high number of outlier blocks (n = 32) were detected, of which 24 (75%) demonstrated spatial clustering and 8 (25%) did not exhibit spatial autocorrelation (Figs. 3g–l and Table S4 ). These findings suggest that the model is sensitive in detecting clusters even when canine L. infantum infection rates are relatively low. At 12 months, the threshold for defining outlier quadrants remained similar, with a limit of 0.3. The number of quadrants with the highest counts of L. infantum infection remained constant at 32 at 12 months, of which 27 (84.4%) formed clusters exhibiting spatial autocorrelation, while 5 (15.6%) were spatially isolated (Table S4 ). At 27 months, the threshold index for outlier blocks increased to greater than 0.34 compared to 12 months, although the total number of outlier blocks decreased to 22. Among these, 15 (68.2%) demonstrated spatial autocorrelation and 7 (31.8%) did not (Table S4 ). The recurrence of outlier blocks over time was relatively low in the control area. Of the 23 outlier blocks identified at baseline, only 2 (8.7%) remained classified as outliers at 12 months (Table S4 ). Furthermore, at 27 months, only 2 of the 26 outlier blocks from 12 months (7.7%) retained their outlier status. In the intervention area, the persistence of clusters between time points was also low. Only one-fifth of the outlier blocks identified at baseline were classified as outliers again at 12 months. Specifically, of the 32 outlier blocks at baseline, 6 (18.7%) continued to exhibit increasing infection rates at 12 months. Between 12 and 27 months, there was greater stability in cluster recurrence, with 7 of the 32 (21.9%) blocks identified as outliers at 12 months maintaining this status at the end of the study (Table S4 ). 3.4. Impact of impregnated collars on sand fly prevalence and distribution Over the 19 months of entomological monitoring, a total 725 sand fly were made in the control area and 697 in the intervention area. A total of 770 specimens of Lu. longipalpis were captured in the intervention area, while 816 specimens were captured in the control area. Analysis using a linear model showed no difference in the average Lu. longipalp in captured in the control versus intervention areas, (mean difference 3.62; p = 0.5281). There was no difference in the average relative abundance of Lu. longipalpis in the intervention and control areas (mean difference 0.29, p = 0.625). No significant difference in the overall household infestation between the control and the intervention areas (mean difference of -11.26; p = 0.059). However, when households without dogs from the intervention area were compared to the control area, significantly higher sand fly infestation was observed in the former (Estimate = + 21.17 sand flies/household; p = 0.0029), Table 5. This indicates that in the absence of dogs wearing insecticide collar, the average infestation level in the intervention was 21.17 per household higher than the control area. Furthermore, within the intervention area, household with collared dogs had significantly lower infestation level compared to dogs without dogs, with a mean reduction of 15.53 sand flies, (p = 0.0459), Table 5. In addition, the mean number of monthly Lu. longipalpis captures per household was analyzed using a time series regression model. A 2.6-fold reduction in the mean number of sand flies was observed in households with dogs wearing insecticide-impregnated collars compared to those without dogs. Households without dogs had a mean vector count of 4.97 ± 4.3 sand flies per month, whereas households with collared dogs had a significantly lower mean of 2.4 ± 2.0. The time series analysis showed reduced variability in sand fly counts in households with collared dogs (standard deviation = 2.0), compared to households without dogs (standard deviation = 4.3), indicating an attenuation in vector population fluctuations in the presence of the intervention. Discussion Canine visceral leishmaniasis is a common parasitic disease in Latin America, particularly in Brazil, but also in Mediterranean Europe. In Brazil, it affects not only dogs in low-income communities, but also those from middle-class households ( 40 , 44 ). Historically, governmental strategies in Brazil focused on culling infected-VL dogs, as treatment was not available or permitted, mostly because the small repertoire of drugs to treat human disease and the fear of resistance ( 45 – 47 ). Recently; however, the Brazilian Minister of Health has recently allowed treatment of canine visceral leishmaniasis with miltefosine for the treatment of canine leishmaniasis ( 48 – 50 ) and for long, dogs have been treated using allopurinol ( 51 ). Despite this, treated dogs with VL often relapse, and infected dogs may be act as reservoirs, even with low level of Leishmania infection ( 52 ). Resistance to miltefosine emerged in India, for the treatment of Indian VL, and while effective for human cutaneous leishmaniasis, as single therapy, in Brazil, its long-term efficacy for cutaneous leishmaniasis remains uncertain ( 53 , 54 ). In the past, discussions have been highlighted the need to novel approach for leishmaniasis treatment, similarly to tuberculosis, using combination s therapy regimen ( 55 ). Serosurvey of canine L. infantum infection conducted previously in our two studied areas showed similar levels of canine Leishmania infection. However, when this current study was initiated a significant difference in L. infantum infection in the two areas was observed. Abrupt variations in canine L. infantum infection rates have already been observed in other longitudinal studies ( 38 , 45 ). Fluctuations in canine L. infantum infection may be associated with seasonal changes in vector density ( 56 , 57 ), as well as the dynamic territorial flow of susceptible and L. infantum -infected individuals and the seroconversion of dogs in the pre-patent infection phase ( 58 ). Vertical or horizontal routes of L. infantum transmission have likely been underestimated and are not well documented, particularly in areas where there competent sand flies, as it is the case of Natal, where this study was performed ( 22 , 59 ). Differences in the demographic and management profiles of the canine population may also have contributed to the higher rate of L. infantum infection observed in the control area. Specifically, dog owners in the control area appeared to adopt fewer preventive measures against infectious and parasitic diseases, potentially increasing their animals' exposure to environmental risk factors for infection. Importantly, sand fly population dynamics were similar across both intervention and control areas, suggesting comparable vector pressure and supporting the assumption that transmission via the traditional vector-borne route occurred at similar intensity in both settings. This reinforces the validity of our relative risk analyses and highlights the complexity of the VL ecoepidemiological system. In our study, the mass application of collars impregnated with 4% deltamethrin significantly reduced the rate of canine infection by L. infantum at 6-month post intervention; but the protective effect at a population level was not sustained. Additionally, a significant reduction in canine infection was also observed in the control area during the first year, likely attributable to the implementation of dog culling strategies. Overall, the collars demonstrated limited effectiveness in reducing canine visceral leishmaniasis (VL) transmission at the population level when deployed under challenging ecoepidemiological conditions—characterized by hyperendemicity and heightened socioeconomic vulnerability. Nevertheless, the use of deltamethrin-impregnated collars proved effective in reducing infantum infection in individual dogs, supporting their role as a complimentary tool in integrated VL control strategies. Studies in other areas showed that insecticide-impregnated collars also presented discreet results regarding their effectiveness in reducing canine infection, such as Reithinger et al. (2004) in a randomized cohort with 441 dogs ( 37 ) and Leite et al. (2018), ( 38 ). Kazimoto et al. (2018) demonstrated a significant reduction in seroprevalence for L. infantum among dogs in the intervention area wearing collars compared to controls after 6 months ( 60 ). All control measures must be critically evaluated to determine their relative impact and role in sustaining Leishmania infantum transmission within a locality. In this context, alternative routes of transmission—such as vertical and horizontal transmission—remain underexplored and are often not adequately considered in current control strategies. A comprehensive understanding of all potential transmission pathways is essential to inform more effective and sustainable interventions. One of the primary factors contributing to the limited effectiveness of impregnated collars in our study was the suboptimal coverage of the target canine population, with only 80% of recruitment achieved. This incomplete coverage, similar to what is observed for vaccination coverage, likely reduced the identification of potential reservoirs and limited the overall reach and impact of the intervention. The main barriers to full recruitment included inaccessible households, owner refusal, aggressive dogs, and logistical difficulties in collar placement. Previous Mathematical models proposed by Reithinger et al. (2004), ( 37 ) and Sevá et al. (2016) showed that to achieve a significant epidemiological impact on canine and human transmission, high coverage (greater than 90%) would be necessary, with rapid replacement of lost or expired collars and collaring of new dogs ( 61 , 62 ). These findings underscore the importance of maximizing intervention coverage and operational efficiency to optimize the impact of this control measure. Loss of canine follow-up was another important limitation of the study. Kazimoto et al. (2018) obtained a 58% loss to follow-up after 6 months of intervention with the collars ( 60 ). Similar sequence losses were observed in two other studies in Brazil ( 37 , 63 ). Change of address, closed homes, refusal of owners and death of animals were the main causes of loss to follow-up in our and other studies. Losses of collars also led to the low effectiveness of the strategy, a limitation of our study, but also has been highlighted by other studies ( 37 ). Despite the low overall effectiveness of collars in reducing canine VL seroprevalence, we observed a significant protective effect against the incidence of L. infantum infection among collared dogs followed throughout the study, with half of the risk of canine infection in relation to dogs followed from the control area at 6 months. Furthermore, a residual effect of the collars beyond 6 months could have provided unexpected protection ( 64 ). The Bayesian model of spatio-temporal distribution of canine L. infantum infection by blocks, associated with transmission risk analysis using the Moran index, delimited clusters with high refinement. Geostatistical studies of VL within smaller, homogeneous urban limits can be important tools for increasing the precision of ecoepidemiological vulnerability and spatial transmission risk analyses, complementing geostatistical approaches in broader spatial units, which are mosaics of ecological heterogeneity for vector breeding. Presence of the spatial dynamics of canine infection by L. infantum within blocks can facilitate planning and optimize operations aimed at controlling canine visceral leishmaniasis. Blocks with an atypical profile of canine infection by L. infantum could arise because of urban landscapes that generate an ecoepidemiological risk for VL, with microenvironments reflecting ideal biotic and abiotic conditions for the development of the vector ( 65 ). In both areas of the study, it is common to have animal shelters, attractive sources of blood meal for sandflies and the occurrence of wastelands with accumulation of organic matter and plant species used as a preferential source of carbohydrates by vectors ( 66 ). A low recurrence of the same clusters was observed between subsequent observations, denoting dynamic changes overtime, with generation and suppression of spatial points of high transmission. Other studies have demonstrated the association of the risk of VL transmission with the population density of dogs and the presence of individuals competent as a reservoir of L. infantum and capable of increasing the basic reproduction number R0 ( 67 , 68 ). The fluctuation of spatial pockets of transmission may have resulted in the suppression, through natural death or removal of highly infectious animals by the surveillance service, followed by the emergence of other priority foci of new individuals with the same profile. The residual effect of the insecticidal action may have influence the density of Lu. longipalpis and the household infestation in the households with dogs that used impregnated collars. The reduction in entomological indicators was also observed in another recent intervention study with impregnated collars carried out in two hyperendemic areas by Silva et al (2018), ( 69 ). In our study, however, it was noticed that household infestation of houses without dogs in the intervention area was significantly higher than in the control area. This finding may reflect in the increase in global vector infestation observed in the intervention area. Prior study in area showed feeding preference of sandflies dogs and humans in the area ( 70 ). This study had several limitations, primary related to logistical and operational challenges in the implementation ( 71 ). These limitations likely contributed to the limited effectiveness of collars impregnated with 4% deltamethrin in reducing L. infantum infection at the population level. Notably, not all infected dogs were euthanized, which may have allowed continued transmission. Additionally, vertical transmission of L. infantum was not considered during the study period. Since then, growing evidence has demonstrated that L. infantum can be transmitted transplacentally, a route that may play a significant role in maintaining the pathogen within the canine population. Effectively interrupting L. infantum transmission to both humans and dogs requires comprehensive public health policies that promote integrated control measures and inter-institutional collaboration. These should include environmental management, dog population control, measures to block vector exposure (e.g., collars or repellents), and continuous health education efforts targeting communities in endemic areas. Declarations Acknowledgements. We thank Mr Alessandre Medeiros ( in Memoriam ) Head of the Center for Zoonosis Control, for his support of the field studies. We also thank the endemic disease agents and employees of the animal management sector, technicians from the immunodiagnostic laboratory and the entomology division of the Center for Zoonosis Control, for their tireless work mitigating the impacts of visceral leishmaniasis on the neediest population and for their essential collaboration in carrying out the study. To the colleagues of the UFRN Institute of Tropical Medicine, Leonardo Rodrigues Pinheiro and Margarita Alexandre Mavromatis, for their administrative support for the project. We also thank the Brazilian Minister of Health for providing the collars for use in this study. Author Contributions J.F.V.C aided the study design, performed enrollment of canine population, data analysis and wrote the first draft of the manuscript. D.C.S.C performed data entering and analysis and prepared figure 2. I.D.L, A.L.M.L, I.G.M aided the recruitment of the human population and collection of blood samples and data entering. P.R.P.N, F.P.F-N, G.R.G.M, J.G.V aided recruitment of human population and performed the serological studies. I.P.S.O performed the sand flies studies. R.L.S aided the drawing of the maps using the shape files. U.P.S.T.S aided the study design and selection of areas. M.A.G.R performed all canine serological studies. R.K.R.L aided the clinical studies. M.E.W performed data analysis and edited and reviewed the manuscript. E.G.C performed data analysis. J.W.Q aided the design, the data analysis and reviewed the first draft of the manuscript. S.M.B.J aided the design of the study, performed recruitment of the human population, sample collection and obtained funding. All authors reviewed and approved the final version of the manuscript. Funding This research was funded, in part, by a grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico, INCT-DT, 465229/2014-0. The collars were provided by the Brazilian Minister of Health. The contents of this publication are the sole responsibility of the authors and do not necessarily reflect the views of the CNPq or the Brazilian Minister of Health. Data Availability Data supporting the main conclusions of this study are included in the manuscript in the text, tables and figures. Ethics approval and consent to participate The protocol for this study was reviewed and approved by the Federal University of Rio Grande do Norte Ethical Committee on human research (CAAE Platform 37529814.1.0000.5537). The protocol for the use of dogs in the research was reviewed and approved by the Research Committee Ethics in the Use of Animals-(CEUA 062/2014). All participants or the legal guardian received information on the research and those who consented were recruited. 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Tables Tables 1 to 5 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Table1.docx Table2.docx Table3.docx Table4.docx Table5.docx TableS1.docx TableS2.docx TableS3r.docx TableS4.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Francisco","middleName":"Paulo","lastName":"Freire-Neto","suffix":""},{"id":513086365,"identity":"d3d67e57-4746-4f86-b5c4-4c9a3fe06651","order_by":7,"name":"Irina Paula Silva Oliveira","email":"","orcid":"","institution":"Unidade de Vigilância das Zoonoses Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Irina","middleName":"Paula Silva","lastName":"Oliveira","suffix":""},{"id":513086366,"identity":"3975795f-fb6b-49d8-9468-81b5b7b52680","order_by":8,"name":"Glória Regina Góis Monteiro","email":"","orcid":"","institution":"Instituto de Medicina Tropical do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Glória","middleName":"Regina 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Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Úrsula","middleName":"Priscila Silva Torres","lastName":"Sousa","suffix":""},{"id":513086370,"identity":"d0050f8b-842f-4d48-b994-56454d22f42b","order_by":12,"name":"Marcos Adriano Gomes Rodrigues","email":"","orcid":"","institution":"Unidade de Vigilância das Zoonoses Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Marcos","middleName":"Adriano Gomes","lastName":"Rodrigues","suffix":""},{"id":513086371,"identity":"6065c765-4c10-4591-91db-82348e1ca244","order_by":13,"name":"Romeika Karla dos Reis Lima","email":"","orcid":"","institution":"Canus \u0026 Catus Especialidades","correspondingAuthor":false,"prefix":"","firstName":"Romeika","middleName":"Karla dos Reis","lastName":"Lima","suffix":""},{"id":513086372,"identity":"cbb84b75-d439-4ed7-9695-17ae6369a843","order_by":14,"name":"Mary Edyth Wilson","email":"","orcid":"","institution":"University of Iowa","correspondingAuthor":false,"prefix":"","firstName":"Mary","middleName":"Edyth","lastName":"Wilson","suffix":""},{"id":513086373,"identity":"e3885ef3-778a-4df6-bae7-e402a0b714fa","order_by":15,"name":"Eliardo Guimarães Costa","email":"","orcid":"","institution":"Instituto de Medicina Tropical do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"Eliardo","middleName":"Guimarães","lastName":"Costa","suffix":""},{"id":513086374,"identity":"5fa3540f-8329-41e8-baf7-9d0b451b31ee","order_by":16,"name":"José Wilton Queiroz","email":"","orcid":"","institution":"Instituto de Medicina Tropical do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal-RN","correspondingAuthor":false,"prefix":"","firstName":"José","middleName":"Wilton","lastName":"Queiroz","suffix":""},{"id":513086375,"identity":"b30f2b7e-b12d-4d43-9c72-acf0ff99c7b9","order_by":17,"name":"Selma Maria Bezerra Jeronimo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6UlEQVRIiWNgGAWjYFAC5gYgwQZmHmBgsGFgB/KZ8WthRNGSxsBzgDgtcHCYsBb59sbWDT8Y+OTM23sPHrpRcT6xR/rsAebCPbi1GJw52Hazh4HNWObMuYTDOWduJ/bw5SUwz3iGR4tEYtsNHga2xBkSOQaHc9tuJ+7n4TFgBrkOp8PmP2y7+YeBrR6q5VxiDyEtDDcY224DbUmQgGg5QFiLwZnEttsyBmyGM3jOGAD9kmwM0nJ4Bj6HtR8+dvNNxTF5CfYe4885FXayQC2GjwvwOQxi1zFUPkENQFBDhJpRMApGwSgYsQAAqOJRlxvWqD8AAAAASUVORK5CYII=","orcid":"","institution":"Instituto de Medicina Tropical do Rio Grande do Norte, Universidade Federal do Rio Grande do Norte, Natal-RN","correspondingAuthor":true,"prefix":"","firstName":"Selma","middleName":"Maria Bezerra","lastName":"Jeronimo","suffix":""}],"badges":[],"createdAt":"2025-08-21 14:23:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7427065/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7427065/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91190722,"identity":"5ccbfc38-0e4f-428f-b812-05bc99f3f0f0","added_by":"auto","created_at":"2025-09-12 14:36:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":6477062,"visible":true,"origin":"","legend":"\u003cp\u003eMap of Brazil indicating the state of Rio Grande do Norte and the city of Natal with the study areas.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/3436bd63fd78ce4ffe0307dc.png"},{"id":91193122,"identity":"2d407284-0bb5-40f3-908b-4dfe4ae801c1","added_by":"auto","created_at":"2025-09-12 14:44:18","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3352644,"visible":true,"origin":"","legend":"\u003cp\u003eThe diagram shows the canine follow-up conducted in the study areas at 0, 6, 12, and 27 months.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e† \u003c/sup\u003eIndicates dogs recruited at the start of the study, while \u003csup\u003e✤\u003c/sup\u003e represents dogs newly recruited at 6, 12, and 27 months.\u003c/p\u003e\n\u003cp\u003e* During the follow-up period, a total of 2592 dogs left the study, while 4987 new recruits were enrolled at T6, T12, and T27.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/64b192af5975e3a91a2dd79b.png"},{"id":91190725,"identity":"cbca2e34-8c7f-4bf3-8a4e-6561027567de","added_by":"auto","created_at":"2025-09-12 14:36:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":6134044,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial dynamics of dog \u003cem\u003eL. infantum\u003c/em\u003e infection in control (a-f) and intervention (g-l) areas at baseline (T0, top), 12 months (middle), and 27 months (bottom). Black blocks indicate outliers.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/ad92f5c2ca6f4cc408c622e0.png"},{"id":94474346,"identity":"1d7df79f-b2e3-471e-9f62-4bbb32fcd4e8","added_by":"auto","created_at":"2025-10-27 15:48:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":16986452,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/5a4011af-438f-4afe-b32a-7e333659ab90.pdf"},{"id":91190715,"identity":"c52197ac-a45b-4eff-81bd-e7fe76451416","added_by":"auto","created_at":"2025-09-12 14:36:18","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":17281,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/f06cea9222bd26941d56064c.docx"},{"id":91190718,"identity":"78d0730b-59be-4e3c-bd15-53a3bab5988c","added_by":"auto","created_at":"2025-09-12 14:36:19","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":21406,"visible":true,"origin":"","legend":"","description":"","filename":"Table2.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/74aad524f7006789c957898b.docx"},{"id":91194404,"identity":"d516e24e-44ad-4b80-abb5-25fd2273b02f","added_by":"auto","created_at":"2025-09-12 14:52:19","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":15771,"visible":true,"origin":"","legend":"","description":"","filename":"Table3.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/18e74efc689738aa2861a876.docx"},{"id":91190719,"identity":"0e9ea521-249c-4df6-bf86-7f6603ffe6d2","added_by":"auto","created_at":"2025-09-12 14:36:19","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":17105,"visible":true,"origin":"","legend":"","description":"","filename":"Table4.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/ad9c3781c1f3aa2bc607c729.docx"},{"id":91193125,"identity":"04585b78-a6b1-4105-8866-b0e3a00541d4","added_by":"auto","created_at":"2025-09-12 14:44:19","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":16376,"visible":true,"origin":"","legend":"","description":"","filename":"Table5.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/6df644bdb1efda046f3e7dda.docx"},{"id":91190724,"identity":"fa195cc0-1b04-4930-80dd-4a7630254e53","added_by":"auto","created_at":"2025-09-12 14:36:19","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":15252,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/c71e4b8c14a79582411e631b.docx"},{"id":91193127,"identity":"55cda6a8-b995-4f12-a9ba-7949a40e8643","added_by":"auto","created_at":"2025-09-12 14:44:19","extension":"docx","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":14808,"visible":true,"origin":"","legend":"","description":"","filename":"TableS2.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/402051a2d665b8b31ea367b1.docx"},{"id":91195894,"identity":"0bebad06-0bbd-4437-a006-ec18e80a2c2b","added_by":"auto","created_at":"2025-09-12 15:00:19","extension":"docx","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":15316,"visible":true,"origin":"","legend":"","description":"","filename":"TableS3r.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/fefa8624c9d937ab14c953ad.docx"},{"id":91193130,"identity":"89bebefa-9ea9-4d68-9313-a636701068f6","added_by":"auto","created_at":"2025-09-12 14:44:19","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":16197,"visible":true,"origin":"","legend":"","description":"","filename":"TableS4.docx","url":"https://assets-eu.researchsquare.com/files/rs-7427065/v1/fea8668505ec94877f45b08e.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eComplexity of implementing canine visceral leishmaniasis control measures at a population level: use of impregnated deltamethrin collars and culling \u003c/p\u003e","fulltext":[{"header":"Background","content":"\u003cp\u003eVisceral leishmaniasis (VL) is a major a vector-borne disease that primarily affects populations living in socioeconomically vulnerable areas, particularly in tropical and subtropical areas of the world (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). Overlapping outbreaks of human and canine VL have been reported in Spain, France and Italy. This illness has a tremendous impact on the canine population in both Europe and Latin America (\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Mortality in untreated dogs is high; however, one study in France reported it to be approximately 30% when antimony was used alone, decreasing when combination therapy was used (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). For humans, 5% of the cases are fatal, even with treatment (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Undernourishment and immunodeficiency increase the risk of VL in both humans and dogs (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). Human co-infection of HIV and \u003cem\u003eLeishmania infantum\u003c/em\u003e was first described in Europe (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Currently, it accounts for approximately 15% of VL cases in Brazil (\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). These individuals more often relapse and they tend to have a greater mortality than uncomplicated VL (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). The introduction of anti-retroviral therapy has decreased the risk of symptomatic human VL (authors observation, Bezerra et all, under revision). In a parallel scenario, undernourished dogs or dogs co-infected with tick-borne pathogens are at increased risk for symptomatic canine VL (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAll Brazilian regions report autochthonous cases of both human and canine VL (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). The adaptability of \u003cem\u003eLutzomyia longipalpis\u003c/em\u003e, the main vector implicated in \u003cem\u003eLeishmania infantum\u003c/em\u003e transmission in South America, to peridomestic areas, together with the presence of highly infected, sustains the endemicity of this pathogen in these areas. The majority of \u003cem\u003eLeishmania\u003c/em\u003e spp. transmission is thought to be vector-borne. However, case reports of human VL in non-endemic areas have documented vertical transmission of \u003cem\u003eL. infantum\u003c/em\u003e (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). In addition, over the past two decades, numerous studies have demonstrated that \u003cem\u003eL. infantum\u003c/em\u003e can be transmitted vertically in dogs, even in regions where no competent sand fly vector is present (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). Typing of those Leishmania isolates showed that they were from western Europe (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eDogs are the main urban reservoir of \u003cem\u003eL. infantum\u003c/em\u003e in Brazil, and in newly endemic VL areas, canine VL often precedes human disease (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). Fran\u0026ccedil;a-Silva et al demonstrated that systematic euthanasia of \u003cem\u003eL. infantum\u003c/em\u003e seropositive dogs can be effective for VL control for both humans and dogs, if routinely maintained (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). Nonetheless, dog culling because of VL remains controversial (\u003cspan additionalcitationids=\"CR28 CR29 CR30\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e), and novel strategies are needed. When people are diagnosed with VL in Brazil, the Ministry of Health usually inspects their dwellings aiming to identify vector breeding sites, and searches for \u003cem\u003eL. infantum\u003c/em\u003e infected dogs. However, there is usually a lag between the diagnosis of human VL and implementation of control measures; which may allow further parasite dissemination. Persistence of \u003cem\u003eL. infantum\u003c/em\u003e in the vertebrate host, particularly in humans, has been documented, adding another layer of complexity for control measures. A study in Brazil reported VL occurring decades after individuals had left the endemic regions, leading the authors to consider \u003cem\u003eL. infantum\u003c/em\u003e as an opportunistic pathogen (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). Supporting this report, a more recent study with United States Military personnel provided evidence of the potential lag between infection and VL development in humans (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eControlled studies have unequivocally demonstrated the efficacy of these collars in repelling insect bites (\u0026gt;\u0026thinsp;90%) and in their insecticidal activity (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). Furthermore, several intervention studies with deltamethrin-impregnated collars, conducted in Europe and Brazil, have evaluated the blockade of \u003cem\u003eL. infantum\u003c/em\u003e transmission in dogs at the population level, with variable effectiveness outcomes. These discrepancies may be attributed to eco-epidemiological differences, experimental design complexity, and operational challenges in strategy implementation and sustainability (\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e). However, due to the complexity of \u003cem\u003eL. infantum\u003c/em\u003e transmission and the limitations of this control model when applied at the community level, the strategy still requires refinement and optimization. Given the importance of decreasing canine \u003cem\u003eL. infantum\u003c/em\u003e infection, this study aimed to evaluate the effectiveness of 4% deltamethrin-impregnated collars on the incidence of \u003cem\u003eL. infantum\u003c/em\u003e infection in dogs, while investigating their influence on the spatial dynamics of parasite transmission and their impact on the abundance and of the vector \u003cem\u003eLutzomyia longipalpis\u003c/em\u003e\u0026mdash;the primary agent of zoonotic transmission.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.1.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eStudy Areas\u003c/em\u003e\u003c/strong\u003e: The study was conducted between 2014-2017 in the north district of Natal, state of Rio Grande do Norte, Brazil, which is endemic for human and canine VL (Figure 1). The city has a population of 877,739 people (IBGE, www.ibge.gov.br). About 37.8% (303.543 people) of the city population live in the north district. The two locations Boa Esperança (intervention) and Jardim Progresso (control), Figure 1, were chosen based on prior surveillance studies for canine \u003cem\u003eL. infantum\u003c/em\u003e infection \u0026nbsp;and reports of human VL (40); from herein on we will use the names of control (Jardim Progresso) and intervention (Boa Esperança) areas. The intervention area had a population of 16,444 inhabitants, residing in an area of 246 blocks, whereas the control area had an estimated population of 17,375 inhabitants spread over 247 blocks. \u0026nbsp;The team members of the Zoonosis Surveillance Unit visited the household and aided with recruitment the dog population. Figure 2 shows the number of dogs recruited and loss to follow up, and the ones that were culled in both areas.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.2.\u0026nbsp; \u0026nbsp; \u0026nbsp;Study Design:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eA prospective non-randomized intervention study was performed between 2014-2017. All blocks from the intervention (n=246) and control areas (n=247) were visited (Table S1). Dogs belonging to consenting owners received polyvinylchloride (PVC) collars impregnated with 4% deltamethrin (40 mg/g concentration), (Scalibor® ProtectorBands, Intervet).Dogs of consenting owners in the control area were followed without collar application. \u0026nbsp;\u003cem\u003eL. infantum\u003c/em\u003e serological surveys were performed at the time of recruitment and 6, 12, and 27 months later. Collars were placed at the time of recruitment and replaced after 6 and 12 months. \u0026nbsp;If authorized, by the dog’s owner, VL dogs, with compatible symptoms and with confirmatory serologic testing, were euthanized by a veterinarian\u0026nbsp;from the Zoonosis Surveillance Unit of the Health Secretariat of Natal (Table S2). A cross-sectional study of \u003cem\u003eL. infantum\u003c/em\u003e infection in humans residing the same house of the recruited dogs at the onset of the study was performed. Information on current and past medical history and vaccination coverage were collected. Blood was drawn and a physical examination was performed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.3.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eLeishmania infantum serological test\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Animals were screened for \u003cem\u003eL. infantum\u003c/em\u003e infection by using the Rapid Dual Path Platform Test (DPP®). Animals whose samples were positive in the screening test were tested using a confirmatory Enzyme Linked Immunosorbent Assay (ElE). Both tests were produced by the Bio-Manguinhos Laboratory (Rio de Janeiro, RJ, Brazil).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.4.\u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eSand fly monitoring:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eThe intervention and control areas were monitored for sand flies for 19 months, between August 2014 and February 2016. Flies were captured using CDC light traps in the peridomicile region surrounding 10 properties selected among these with fruit trees, organic debris-trash presence and in proximity of human VL case diagnosed within the last 4 years. In the intervention area, traps were distributed in houses with collared dogs (n=5 houses) and without dogs (n=5 houses). Traps were placed at 5:00 p.m. and collected at 6:00 a.m. Sand flies were placed in tubes with 70% ethyl alcohol and species were identified using Galati's classification\u0026nbsp;(41,42). The relative abundance of sand flies – defined as the total number of vectors captured monthly divided by the number of households surveyed – home infestation, defined as the percentage of properties with vectors relative to the total number of properties surveyed, and the relative abundance of male versus female \u003cem\u003eLu. longipalpis\u003c/em\u003e were determined.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.5. Spatial base analysis used in data plotting:\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eThe maps of the Intervention Area and Control Area subdivisions were generated from the SHAPEs of the census tracts, (43).The free software QGIS multiplatform (version 2.18) was used to process the maps, which allowed the visualization, editing and analysis of georeferenced data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e2.6. Statistical analysis\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e:\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eStatistical comparisons between population characteristics were done by Chi Square test. \u003cem\u003eL. infantum\u003c/em\u003e ELISA data were compared between populations as odds ratios, and or relative risk. The impact of collars on sand fly density were compared by linear or logistical regression. The relationship between \u003cem\u003eL. infantum\u003c/em\u003e infections in dogs and humans within or between the areas were determined with a combination of odds ratios and the Mantel-Haenszel statistic. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe dynamics of spatial autocorrelation of canine\u003cem\u003e\u0026nbsp;L. infantum\u0026nbsp;\u003c/em\u003einfectionby block was performed using a Local Empirical Bayesian Estimator, consisting of the local infection rate weighted by the rates of neighboring blocks. For each map, its Moran Scatter Diagram was drawn, with two-dimensional scatterplot.\u003c/p\u003e\n\u003cp\u003eLinear models were adjusted with the location dummy variable to evaluate the effect of the presence of collars impregnated with deltamethrin on sand flies assessing relative abundance and household infestation. The means of the monthly series of entomological indicators from the intervention and control areas were compared. The means were stratified considering whether the household had dogs with collars or not. The significance of the local differential effect was determined by Student's t test.\u003c/p\u003e\n\u003cp\u003eOdds ratios (ORs) for \u003cem\u003eL. infantum\u003c/em\u003e infection in humans and dogs were calculated with 95% confidence intervals. A weighting formula was used to compute the Common Odds Ratio (COR), combining data from both areas. Conditional independence between infection status and species was tested Mantel-Haenszel statistic, which adjusts for potential confounders and provides a chi-square and p-value to assess the significance of the findings.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStatistical analyses and graphical representations were performed using R Studio version 1.1.383 and R-System version 3.4.1 software.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.7. Ethical Considerations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe protocol was reviewed and approved by the Federal University of Rio Grande do Norte Ethical Committee on human research (CAAE Platform 37529814.1.0000.5537). The protocol for the use of dogs in the research was reviewed and approved by the Research Committee Ethics in the Use of Animals-(CEUA 062/2014). All participants or the legal guardian received information on the research and those who consented were recruited. Only dogs that the owner consented were recruited into the study.\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cb\u003e3.1. Human and canine\u003c/b\u003e \u003cb\u003eLeishmania infantum\u003c/b\u003e \u003cb\u003einfections at the onset of the study\u003c/b\u003e\u003c/p\u003e\u003cp\u003eCanine \u003cem\u003eL. infantum\u003c/em\u003e infections were initially screened by DPP, and positives were confirmed by EIE. Human \u003cem\u003eL. infantum\u003c/em\u003e infection was assessed by an in-house ELISA using soluble leishmania antigens (SLA) from a local isolate. At the onset of the study, 2,873 dogs recruited, 1,271 and 1,602 from the intervention and control areas, respectively, (Fig.\u0026nbsp;2). Unexpectedly, household characteristics and dog care differed between the two localities (Table\u0026nbsp;1). Dogs from the intervention area had higher vaccination coverage, had better availability of food and fewer signs of VL (Table\u0026nbsp;1). Overall, 9.9% in the intervention area and 19.6% of the dogs from control areas tested positive for \u003cem\u003eL. infantum\u003c/em\u003e infection by serology. The prevalence of \u003cem\u003eL. infantum\u003c/em\u003e infection was higher in the control than in the intervention area, with an odds ratio 0.454 (95%, CI 0.364, 0.566), for dogs positive in the intervention area versus control area, indicating a greater risk of infection in the latter (Table\u0026nbsp;2).\u003c/p\u003e\u003cp\u003eAt the onset of the study, \u003cem\u003eL. infantum\u003c/em\u003e seropositivity in people was 4.4% (51/1156) in the intervention area and 14.3% (80/557) in the control areas (Table\u0026nbsp;3). In the intervention area, the odds of \u003cem\u003eL. infantum\u003c/em\u003e infection in dogs compared with humans was 2.4, whereas in the control area was 1.46. The common odds ratio (COR) across both areas was 1.78 (95%CI: 1.44\u0026ndash;2.19), with the use of a Mantel-Haenszel statistic equaling to 27.53 (df\u0026thinsp;=\u0026thinsp;1,p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.001). These findings provide evidence of the dependence between \u003cem\u003eL. infantum\u003c/em\u003e human and canine \u003cem\u003eL. infantum\u003c/em\u003e infections (Table\u0026nbsp;3).\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.2. Dynamics of canine\u003c/b\u003e \u003cb\u003eL. infantum\u003c/b\u003e \u003cb\u003einfection\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDuring the 27-month observation period, a total of 11,285 dog evaluations were performed, as shown in Fig.\u0026nbsp;2. The enrolled canine population at onset of the study was re-evaluated 6 and 12 months, coinciding with collars were replacement. At the 6-month mark, there was a 53.6% (632/1179) loss to follow up in the intervention area, and 62.5% (935/1,495) in the control area. During the same period, 742 new dogs were enrolled in the intervention area and 1,087 in the control area. Dogs were withdrawn from the study because of adverse reactions or owner's decision and other causes (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe prevalence of \u003cem\u003eL. infantum\u003c/em\u003e infection at baseline was 6.3% in the intervention area and 13.1% in the control area (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0156). However, at 12 months, no difference was observed, OR 0.970 [ 95% CI: (0.760 to 1.239)], between the groups (Table\u0026nbsp;2). At 27 months\u0026mdash;approximately nine months after the expected duration of collar efficacy\u0026mdash;the estimated OR was 1.048 (95% CI: 0.847 to 1.298), again demonstrating no significant difference in infection status between the intervention and control areas. These analyses incorporated both incident cases among dogs newly enrolled at 6, 12, and 27 months, as well as data from dogs followed longitudinally. Notably, the only time point at which a significant difference in infection status was observed between study arms was at 6 months (Table\u0026nbsp;2).\u003c/p\u003e\u003cp\u003eOf the dogs initially enrolled, only 102 and 179, respectively, from the control and in the intervention areas were monitored at all four time points: baseline, and follow-ups at 6, 12 and 27 months), (Fig.\u0026nbsp;2). Notably, 40.6% of dogs (222 of 547) dogs followed over time had either lost their collars or had them removed by owners prior to the recommended 6-month interval for replacement interval. The primary causes for collar loss or removal included were adverse reactions, voluntary removal by the owners and incidents such as interactions with other dogs (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSeroconversion rates among dogs in the areas are shown in Table\u0026nbsp;4. Among the 432 dogs that were seronegative at baseline, in the control areas, 33 seroconverted at 6 months (7.6% conversion). In comparison, of the 454 seronegative dogs in the intervention area, 15 seroconverted (3.3%). The estimated relative risk of \u003cem\u003eL. infantum\u003c/em\u003e seroconvertion infection was 0.4653 (95% CI: 0.2557, 0.8469, p-0.0101). This indicated that dogs wearing the insecticidal collars had approximately half the risk of becoming \u003cem\u003eL. infantum\u003c/em\u003e infected when serological testing was used as a diagnostic tool.\u003c/p\u003e\u003cp\u003eAt 12-month follow-up, 29 of the 303 dogs in the control area seroconverted, corresponding to a seroconversion rate of 9.6% (Table\u0026nbsp;4). In comparison, 20 of 343 dogs in the intervention area seroconverted (5.8%). The relative risk (RR) of seroconversion in the intervention group compared to the control group was 0.6092 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0732),\u003c/p\u003e\u003cp\u003eAt 27 months of follow-up, a further reduction in the relative risk (RR) of seroconversion was observed between the intervention and control areas, with an RR of 0.3561 (p\u0026thinsp;=\u0026thinsp;0.0418), despite more than one year having passed since the last collar replacement (Table\u0026nbsp;4). In the control area, 10.1% of the 99 dogs monitored seroconverted, compared to 4.2% (26 of 139) in the intervention area (Table\u0026nbsp;4).\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.3. Spatial dynamics of dog\u003c/b\u003e \u003cb\u003eL. infantum\u003c/b\u003e \u003cb\u003einfection in the intervention and control areas.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo evaluate potential spatial clustering of \u003cem\u003eL. infantum\u003c/em\u003e infection among dogs, we analyzed the distribution of cases at the block level within each neighborhood. Figure\u0026nbsp;3 presents maps identifying blocks containing seropositive dogs. Using empirical Bayesian estimation to calculate the number of cases per block, and Moran\u0026rsquo;s I statistic to assess spatial autocorrelation, the neighborhood averages are displayed on the y-axis. Block values are represented using color-coded boxplots: red squares indicate values between the median and the third quartile; green squares represent values between the third quartile and the upper whisker; and black squares denote outliers above this upper limit. The estimated correlation coefficients, representing deviations in case counts for each block relative to the mean of its immediate neighbors, are shown in Figs.\u0026nbsp;3a, 3b, and 3c for the control area, and Figs.\u0026nbsp;3d, 3e, and 3f for the intervention area. Corresponding scatter plots are displayed in Figs.\u0026nbsp;3g, 3h, and 3i for the control area, and Figs.\u0026nbsp;3j, 3k, and 3l for the intervention area.\u003c/p\u003e\u003cp\u003eIn the control area at baseline (time 0), blocks with a spatial index above 0.79 were classified as outliers, as illustrated in the Moran scatterplots (Fig.\u0026nbsp;3d). Blocks with high ordinate values indicated spatial clustering of infection, where adjacent blocks also exhibited high infection rates, whereas blocks with ordinate values near zero were spatially isolated in terms of infection. For instance, as shown in Fig.\u0026nbsp;3d, blocks 512, 514, and 518 were identified as outliers with neighboring blocks displaying high average incidence, indicating spatial autocorrelation. In contrast, blocks 586 and 612 were also outliers but had neighboring blocks with low average incidence, reflecting spatial independence.\u003c/p\u003e\u003cp\u003eAt baseline, 23 outlier blocks were identified in the control area, of which 18 (78.3%) exhibited spatial autocorrelation and 5 (21.7%) did not (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). After 12 months, although the threshold infection rate defining outliers decreased to 0.37, the number of outlier blocks increased to 26, with 18 (69.2%) showing spatial autocorrelation and 8 (30.8%) remaining spatially independent. By 27 months, the threshold for outlier classification rose again to 0.41, and the number of outlier blocks increased further to 30, including 19 (63.3%) with spatial autocorrelation and 11 (36.7%) without evidence of spatial grouping (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eClusters might be more readily identifiable in regions with low case numbers, whereas areas with higher infection densities may approach saturation, potentially masking clustering patterns. At baseline, the intervention area exhibited outlier blocks with indices above 0.31, a threshold lower than that observed in the control area alone. Notably, a high number of outlier blocks (n\u0026thinsp;=\u0026thinsp;32) were detected, of which 24 (75%) demonstrated spatial clustering and 8 (25%) did not exhibit spatial autocorrelation (Figs.\u0026nbsp;3g\u0026ndash;l and Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). These findings suggest that the model is sensitive in detecting clusters even when canine \u003cem\u003eL. infantum\u003c/em\u003e infection rates are relatively low. At 12 months, the threshold for defining outlier quadrants remained similar, with a limit of 0.3.\u003c/p\u003e\u003cp\u003eThe number of quadrants with the highest counts of \u003cem\u003eL. infantum\u003c/em\u003e infection remained constant at 32 at 12 months, of which 27 (84.4%) formed clusters exhibiting spatial autocorrelation, while 5 (15.6%) were spatially isolated (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). At 27 months, the threshold index for outlier blocks increased to greater than 0.34 compared to 12 months, although the total number of outlier blocks decreased to 22. Among these, 15 (68.2%) demonstrated spatial autocorrelation and 7 (31.8%) did not (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe recurrence of outlier blocks over time was relatively low in the control area. Of the 23 outlier blocks identified at baseline, only 2 (8.7%) remained classified as outliers at 12 months (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Furthermore, at 27 months, only 2 of the 26 outlier blocks from 12 months (7.7%) retained their outlier status. In the intervention area, the persistence of clusters between time points was also low. Only one-fifth of the outlier blocks identified at baseline were classified as outliers again at 12 months. Specifically, of the 32 outlier blocks at baseline, 6 (18.7%) continued to exhibit increasing infection rates at 12 months. Between 12 and 27 months, there was greater stability in cluster recurrence, with 7 of the 32 (21.9%) blocks identified as outliers at 12 months maintaining this status at the end of the study (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.4. Impact of impregnated collars on sand fly prevalence and distribution\u003c/b\u003e\u003c/p\u003e\u003cp\u003eOver the 19 months of entomological monitoring, a total 725 sand fly were made in the control area and 697 in the intervention area. A total of 770 specimens of \u003cem\u003eLu. longipalpis\u003c/em\u003e were captured in the intervention area, while 816 specimens were captured in the control area. Analysis using a linear model showed no difference in the average \u003cem\u003eLu. longipalp\u003c/em\u003ein captured in the control versus intervention areas, (mean difference 3.62; p\u0026thinsp;=\u0026thinsp;0.5281). There was no difference in the average relative abundance of \u003cem\u003eLu. longipalpis\u003c/em\u003e in the intervention and control areas (mean difference 0.29, p\u0026thinsp;=\u0026thinsp;0.625).\u003c/p\u003e\u003cp\u003eNo significant difference in the overall household infestation between the control and the intervention areas (mean difference of -11.26; p\u0026thinsp;=\u0026thinsp;0.059). However, when households without dogs from the intervention area were compared to the control area, significantly higher sand fly infestation was observed in the former (Estimate\u0026thinsp;=\u0026thinsp;+\u0026thinsp;21.17 sand flies/household; p\u0026thinsp;=\u0026thinsp;0.0029), Table\u0026nbsp;5. This indicates that in the absence of dogs wearing insecticide collar, the average infestation level in the intervention was 21.17 per household higher than the control area. Furthermore, within the intervention area, household with collared dogs had significantly lower infestation level compared to dogs without dogs, with a mean reduction of 15.53 sand flies, (p\u0026thinsp;=\u0026thinsp;0.0459), Table\u0026nbsp;5.\u003c/p\u003e\u003cp\u003eIn addition, the mean number of monthly \u003cem\u003eLu. longipalpis\u003c/em\u003e captures per household was analyzed using a time series regression model. A 2.6-fold reduction in the mean number of sand flies was observed in households with dogs wearing insecticide-impregnated collars compared to those without dogs. Households without dogs had a mean vector count of 4.97\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3 sand flies per month, whereas households with collared dogs had a significantly lower mean of 2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0. The time series analysis showed reduced variability in sand fly counts in households with collared dogs (standard deviation\u0026thinsp;=\u0026thinsp;2.0), compared to households without dogs (standard deviation\u0026thinsp;=\u0026thinsp;4.3), indicating an attenuation in vector population fluctuations in the presence of the intervention.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eCanine visceral leishmaniasis is a common parasitic disease in Latin America, particularly in Brazil, but also in Mediterranean Europe. In Brazil, it affects not only dogs in low-income communities, but also those from middle-class households (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e). Historically, governmental strategies in Brazil focused on culling infected-VL dogs, as treatment was not available or permitted, mostly because the small repertoire of drugs to treat human disease and the fear of resistance (\u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e). Recently; however, the Brazilian Minister of Health has recently allowed treatment of canine visceral leishmaniasis with miltefosine for the treatment of canine leishmaniasis (\u003cspan additionalcitationids=\"CR49\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e) and for long, dogs have been treated using allopurinol (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e). Despite this, treated dogs with VL often relapse, and infected dogs may be act as reservoirs, even with low level of Leishmania infection (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e). Resistance to miltefosine emerged in India, for the treatment of Indian VL, and while effective for human cutaneous leishmaniasis, as single therapy, in Brazil, its long-term efficacy for cutaneous leishmaniasis remains uncertain (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e). In the past, discussions have been highlighted the need to novel approach for leishmaniasis treatment, similarly to tuberculosis, using combination s therapy regimen (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSerosurvey of canine \u003cem\u003eL. infantum\u003c/em\u003e infection conducted previously in our two studied areas showed similar levels of canine Leishmania infection. However, when this current study was initiated a significant difference in \u003cem\u003eL. infantum\u003c/em\u003e infection in the two areas was observed. Abrupt variations in canine \u003cem\u003eL. infantum\u003c/em\u003e infection rates have already been observed in other longitudinal studies (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e). Fluctuations in canine \u003cem\u003eL. infantum\u003c/em\u003e infection may be associated with seasonal changes in vector density (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e), as well as the dynamic territorial flow of susceptible and \u003cem\u003eL. infantum\u003c/em\u003e-infected individuals and the seroconversion of dogs in the pre-patent infection phase (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eVertical or horizontal routes of \u003cem\u003eL. infantum\u003c/em\u003e transmission have likely been underestimated and are not well documented, particularly in areas where there competent sand flies, as it is the case of Natal, where this study was performed (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e). Differences in the demographic and management profiles of the canine population may also have contributed to the higher rate of \u003cem\u003eL. infantum\u003c/em\u003e infection observed in the control area. Specifically, dog owners in the control area appeared to adopt fewer preventive measures against infectious and parasitic diseases, potentially increasing their animals' exposure to environmental risk factors for infection. Importantly, sand fly population dynamics were similar across both intervention and control areas, suggesting comparable vector pressure and supporting the assumption that transmission via the traditional vector-borne route occurred at similar intensity in both settings. This reinforces the validity of our relative risk analyses and highlights the complexity of the VL ecoepidemiological system.\u003c/p\u003e\u003cp\u003eIn our study, the mass application of collars impregnated with 4% deltamethrin significantly reduced the rate of canine infection by \u003cem\u003eL. infantum\u003c/em\u003e at 6-month post intervention; but the protective effect at a population level was not sustained. Additionally, a significant reduction in canine infection was also observed in the control area during the first year, likely attributable to the implementation of dog culling strategies. Overall, the collars demonstrated limited effectiveness in reducing canine visceral leishmaniasis (VL) transmission at the population level when deployed under challenging ecoepidemiological conditions\u0026mdash;characterized by hyperendemicity and heightened socioeconomic vulnerability. Nevertheless, the use of deltamethrin-impregnated collars proved effective in reducing infantum infection in individual dogs, supporting their role as a complimentary tool in integrated VL control strategies. Studies in other areas showed that insecticide-impregnated collars also presented discreet results regarding their effectiveness in reducing canine infection, such as Reithinger et al. (2004) in a randomized cohort with 441 dogs (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e) and Leite et al. (2018), (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e). Kazimoto et al. (2018) demonstrated a significant reduction in seroprevalence \u003cem\u003efor L. infantum\u003c/em\u003e among dogs in the intervention area wearing collars compared to controls after 6 months (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e). All control measures must be critically evaluated to determine their relative impact and role in sustaining \u003cem\u003eLeishmania infantum\u003c/em\u003e transmission within a locality. In this context, alternative routes of transmission\u0026mdash;such as vertical and horizontal transmission\u0026mdash;remain underexplored and are often not adequately considered in current control strategies. A comprehensive understanding of all potential transmission pathways is essential to inform more effective and sustainable interventions.\u003c/p\u003e\u003cp\u003eOne of the primary factors contributing to the limited effectiveness of impregnated collars in our study was the suboptimal coverage of the target canine population, with only 80% of recruitment achieved. This incomplete coverage, similar to what is observed for vaccination coverage, likely reduced the identification of potential reservoirs and limited the overall reach and impact of the intervention. The main barriers to full recruitment included inaccessible households, owner refusal, aggressive dogs, and logistical difficulties in collar placement. Previous Mathematical models proposed by Reithinger et al. (2004), (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e) and Sev\u0026aacute; et al. (2016) showed that to achieve a significant epidemiological impact on canine and human transmission, high coverage (greater than 90%) would be necessary, with rapid replacement of lost or expired collars and collaring of new dogs (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e). These findings underscore the importance of maximizing intervention coverage and operational efficiency to optimize the impact of this control measure.\u003c/p\u003e\u003cp\u003eLoss of canine follow-up was another important limitation of the study. Kazimoto et al. (2018) obtained a 58% loss to follow-up after 6 months of intervention with the collars (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e). Similar sequence losses were observed in two other studies in Brazil (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e). Change of address, closed homes, refusal of owners and death of animals were the main causes of loss to follow-up in our and other studies. Losses of collars also led to the low effectiveness of the strategy, a limitation of our study, but also has been highlighted by other studies (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eDespite the low overall effectiveness of collars in reducing canine VL seroprevalence, we observed a significant protective effect against the incidence of \u003cem\u003eL. infantum\u003c/em\u003e infection among collared dogs followed throughout the study, with half of the risk of canine infection in relation to dogs followed from the control area at 6 months. Furthermore, a residual effect of the collars beyond 6 months could have provided unexpected protection (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe Bayesian model of spatio-temporal distribution of canine \u003cem\u003eL. infantum\u003c/em\u003e infection by blocks, associated with transmission risk analysis using the Moran index, delimited clusters with high refinement. Geostatistical studies of VL within smaller, homogeneous urban limits can be important tools for increasing the precision of ecoepidemiological vulnerability and spatial transmission risk analyses, complementing geostatistical approaches in broader spatial units, which are mosaics of ecological heterogeneity for vector breeding. Presence of the spatial dynamics of canine infection by \u003cem\u003eL. infantum\u003c/em\u003e within blocks can facilitate planning and optimize operations aimed at controlling canine visceral leishmaniasis.\u003c/p\u003e\u003cp\u003eBlocks with an atypical profile of canine infection by \u003cem\u003eL. infantum\u003c/em\u003e could arise because of urban landscapes that generate an ecoepidemiological risk for VL, with microenvironments reflecting ideal biotic and abiotic conditions for the development of the vector (\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e). In both areas of the study, it is common to have animal shelters, attractive sources of blood meal for sandflies and the occurrence of wastelands with accumulation of organic matter and plant species used as a preferential source of carbohydrates by vectors (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eA low recurrence of the same clusters was observed between subsequent observations, denoting dynamic changes overtime, with generation and suppression of spatial points of high transmission. Other studies have demonstrated the association of the risk of VL transmission with the population density of dogs and the presence of individuals competent as a reservoir of \u003cem\u003eL. infantum\u003c/em\u003e and capable of increasing the basic reproduction number R0 (\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e). The fluctuation of spatial pockets of transmission may have resulted in the suppression, through natural death or removal of highly infectious animals by the surveillance service, followed by the emergence of other priority foci of new individuals with the same profile.\u003c/p\u003e\u003cp\u003eThe residual effect of the insecticidal action may have influence the density of \u003cem\u003eLu. longipalpis\u003c/em\u003e and the household infestation in the households with dogs that used impregnated collars. The reduction in entomological indicators was also observed in another recent intervention study with impregnated collars carried out in two hyperendemic areas by Silva et al (2018), (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn our study, however, it was noticed that household infestation of houses without dogs in the intervention area was significantly higher than in the control area. This finding may reflect in the increase in global vector infestation observed in the intervention area. Prior study in area showed feeding preference of sandflies dogs and humans in the area (\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThis study had several limitations, primary related to logistical and operational challenges in the implementation (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e). These limitations likely contributed to the limited effectiveness of collars impregnated with 4% deltamethrin in reducing \u003cem\u003eL. infantum\u003c/em\u003e infection at the population level. Notably, not all infected dogs were euthanized, which may have allowed continued transmission. Additionally, vertical transmission of \u003cem\u003eL. infantum\u003c/em\u003e was not considered during the study period. Since then, growing evidence has demonstrated that \u003cem\u003eL. infantum\u003c/em\u003e can be transmitted transplacentally, a route that may play a significant role in maintaining the pathogen within the canine population. Effectively interrupting L. \u003cem\u003einfantum\u003c/em\u003e transmission to both humans and dogs requires comprehensive public health policies that promote integrated control measures and inter-institutional collaboration. These should include environmental management, dog population control, measures to block vector exposure (e.g., collars or repellents), and continuous health education efforts targeting communities in endemic areas.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe thank Mr Alessandre Medeiros (\u003cem\u003ein Memoriam\u003c/em\u003e) Head of the Center for Zoonosis Control, for his support of the field studies. We also thank the endemic disease agents and employees of the animal management sector, technicians from the immunodiagnostic laboratory and the entomology division of the Center for Zoonosis Control, for their tireless work mitigating the impacts of visceral leishmaniasis on the neediest population and for their essential collaboration in carrying out the study. To the colleagues of the UFRN Institute of Tropical Medicine, Leonardo Rodrigues Pinheiro and Margarita Alexandre Mavromatis, for their administrative support for the project. We also thank the Brazilian Minister of Health for providing the collars for use in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ.F.V.C \u0026nbsp;aided the study design, performed enrollment of canine population, data analysis and wrote the first draft of the manuscript. D.C.S.C performed data entering and analysis and prepared figure 2. I.D.L, A.L.M.L, I.G.M aided the recruitment of the human population and collection of blood samples and data entering. P.R.P.N, F.P.F-N, G.R.G.M, J.G.V aided recruitment of human population and performed the serological studies. I.P.S.O performed the sand flies studies. R.L.S aided the drawing of the maps using the shape files. U.P.S.T.S aided the study design and selection of areas. M.A.G.R performed all canine serological studies. R.K.R.L aided the clinical studies. M.E.W performed data analysis and edited and reviewed the manuscript. E.G.C performed data analysis. J.W.Q aided the design, the data analysis and reviewed the first draft of the manuscript. S.M.B.J aided the design of the study, performed recruitment of the human population, sample collection and obtained funding. All authors reviewed and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded, in part, by a grant from Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico, INCT-DT, 465229/2014-0. The collars were provided by the Brazilian Minister of Health. The contents of this publication are the sole responsibility of the authors and do not necessarily reflect the views of the CNPq or the Brazilian Minister of Health.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData supporting the main conclusions of this study are included in the manuscript in the text, tables and figures.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe protocol for this study was reviewed and approved by the Federal University of Rio Grande do Norte Ethical Committee on human research (CAAE Platform 37529814.1.0000.5537). The protocol for the use of dogs in the research was reviewed and approved by the Research Committee Ethics in the Use of Animals-(CEUA 062/2014). All participants or the legal guardian received information on the research and those who consented were recruited. Only dogs that the owner consented were recruited into the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication.\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBern C, Maguire JH, Alvar J. Complexities of assessing the disease burden attributable to leishmaniasis. PLoS Negl Trop Dis. 2008;2(10).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlvar J, Yactayo S, Bern C. Leishmaniasis and poverty. Trends Parasitol. 2006;22(12):552\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFran\u0026ccedil;a-Silva JC, Giunchetti RC, Mariano RM da S, Machado-Coelho GLL, Teixeira L de AS, Barata RA, et al. 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Rev Bras Parasitol Vet. 2024;33(1).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVaz TP, Quaresma PF, R\u0026ecirc;go FD, Souza CB, Fontes G, Gontijo CMF. Clinical and Laboratory Response of Domiciled Dogs with Visceral Leishmaniasis Treated with Miltefosine and Allopurinol. Trop Med Infect Dis [Internet]. 2023 Oct 10 [cited 2025 Aug 15];8(10). Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.ncbi.nlm.nih.gov/pubmed/37888600\u003c/span\u003e\u003cspan address=\"http://www.ncbi.nlm.nih.gov/pubmed/37888600\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSarquis J, Raposo LM, Sanz CR, Montoya A, Barrera JP, Checa R, et al. Relapses in canine leishmaniosis: risk factors identified through mixed-effects logistic regression. 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Lancet Infect Dis. 2024;24(1):e36\u0026ndash;46.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHolcman MM, Sampaio SMP, Rangel O and, Casanova C. Spatial and seasonal distribution of Lutzomyia longipalpis in Dracena, a city in the western region of the State of S\u0026atilde;o Paulo, Brazil, that is endemic with visceral leishmaniasis. Rev Soc Bras Med Trop. 2013;46(6):704\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSaraiva L, Leite CG, Lima ACVMDR, de Carvalho LOA, Pereira AAS, Rugani JMN, et al. Seasonality of sand flies (Diptera: Psychodidae) and Leishmania DNA detection in vector species in an area with endemic visceral leishmaniasis. Mem Inst Oswaldo Cruz. 2017;112(4):309\u0026ndash;18.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCourtenay O, Quinnell RJ, Garcez LM, Shaw JJ, Dye C. Infectiousness in a cohort of brazilian dogs: why culling fails to control visceral leishmaniasis in areas of high transmission. J Infect Dis. 2002;186(9):1314\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOzanne M V., Brown GD, Toepp AJ, Scorza BM, Oleson JJ, Wilson ME, et al. Bayesian compartmental models and associated reproductive numbers for an infection with multiple transmission modes. Biometrics. 2020;76(3):711\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKazimoto TA, Amora SSA, Figueiredo FB, Magalh\u0026atilde;es JM e, Freitas YBN, Sousa MLR, et al. Impact of 4% Deltamethrin-Impregnated Dog Collars on the Prevalence and Incidence of Canine Visceral Leishmaniasis. Vector-Borne Zoonotic Dis. 2018;18(7):356\u0026ndash;63.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLopes EG, Sev\u0026aacute; AP, Ferreira F, Nunes CM, Keid LB, Hiramoto RM, et al. Vaccine effectiveness and use of collar impregnated with insecticide for reducing incidence of Leishmania infection in dogs in an endemic region for visceral leishmaniasis, in Brazil. Epidemiol Infect. 2018;146(3):401\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSev\u0026aacute; AP, Ovallos FG, Amaku M, Carrillo E, Moreno J, Galati EAB, et al. Canine-Based Strategies for Prevention and Control of Visceral Leishmaniasis in Brazil. PLoS One. 2016;11(7):e0160058.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLeite BMM, Solc\u0026agrave; M da S, Santos LCS, Coelho LB, Amorim LDAF, Donato LE, et al. The mass use of deltamethrin collars to control and prevent canine visceral leishmaniasis: A field effectiveness study in a highly endemic area. PLoS Negl Trop Dis [Internet]. 2018 May 14 [cited 2025 Aug 15];12(5). Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://pubmed.ncbi.nlm.nih.gov/29758031/\u003c/span\u003e\u003cspan address=\"https://pubmed.ncbi.nlm.nih.gov/29758031/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePaulin S, Fr\u0026eacute;nais R, Thomas E, Baldwin PM. Laboratory assessment of the anti-feeding effect for up to 12 months of a slow release deltamethrin collar (Scalibor\u0026reg;) against the sand fly Phlebotomus perniciosus in dogs. Parasites and Vectors. 2018;11(1).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXimenes M de F de M, Castell\u0026oacute;n EG, Souza M de F de, Menezes AAL, Queiroz JW, Silva VPM e, et al. Effect of Abiotic Factors on Seasonal Population Dynamics of Lutzomyia longipalpis (Diptera: Psychodidae) in Northeastern Brazil. J Med Entomol. 2006;43(5):990\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbbasi I, Trancoso Lopo de Queiroz A, Kirstein OD, Nasereddin A, Horwitz BZ, Hailu A, et al. Plant-feeding phlebotomine sand flies, vectors of leishmaniasis, prefer \u003cem\u003eCannabis sativa\u003c/em\u003e. Proc Natl Acad Sci. 2018;115(46):201810435.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHernandez HG, Brown GD, Lima ID, Coutinho JF, Wilson ME, Nascimento ELT, et al. Hierarchical spatiotemporal modeling of human visceral leishmaniasis in Rio Grande do Norte, Brazil. PLoS Negl Trop Dis. 2023;17(4).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWoolhouse MEJ, Dye C, Etard J-F, Smith T, Charlwood JD, Garnett GP, et al. Heterogeneities in the transmission of infectious agents: Implications for the design of control programs. Proc Natl Acad Sci. 1997;94(1):338\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ee Silva RA, de Andrade AJ, Quint BB, Raffoul GES, Werneck GL, Rangel EF, et al. Effectiveness of dog collars impregnated with 4% deltamethrin in controlling visceral leishmaniasis in Lutzomyia longipalpis (Diptera: Psychodidade: Phlebotominae) populations. Mem Inst Oswaldo Cruz. 2018;113(5):1\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMacedo-Silva VP, Martins DRA, De Queiroz PVS, Pinheiro MPG, Freire CCM, Queiroz JW, et al. Feeding Preferences of Lutzomyia longipalpis (Diptera: Psychodidae), the Sand Fly Vector, for Leishmania infantum (Kinetoplastida: Trypanosomatidae). J Med Entomol. 2014;51(1):237\u0026ndash;44.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlves EB, Figueiredo FB, Rocha MF, Werneck GL. Dificuldades operacionais no uso de coleiras caninas impregnadas com inseticida para o controle da leishmaniose visceral, Montes Claros, MG, 2012. Epidemiol e Serv saude Rev do Sist Unico Saude do Bras. 2018;27(4):e2017469.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 5 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Canine visceral leishmaniasis, Leishmania infantum, collars impregnated deltamethrin, Lutzomyia longipalpis, spatial dynamics","lastPublishedDoi":"10.21203/rs.3.rs-7427065/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7427065/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eIn Brazil, dogs are considered the main reservoir for \u003cem\u003eLeishmania infantum\u003c/em\u003e, the main causative agent of visceral leishmaniasis (VL) for dogs and humans. The goal of this study was to evaluate the effectiveness of deltamethrin impregnated collars for controlling of canine \u003cem\u003eL. infantum\u003c/em\u003e infection.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eA prospective case-control intervention study was performed in paired neighborhoods, implementing deltamethrin-impregnated collars in one area and culling VL dogs in both. Four cross-sectional serosurvey of canine, and one of human \u003cem\u003eL. infantum\u003c/em\u003e infections were performed. Sand flies were monitored along 19 months. Bayesian model and Moran\u0026rsquo;s index of canine \u003cem\u003eL. infantum\u003c/em\u003e infection rates were used to detect spatial autocorrelation.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eA total of 11,285 dog evaluations were performed over 27 months. At baseline, rates of canine \u003cem\u003eL. infantum\u003c/em\u003e infection differed between areas: 10% in the intervention and 19.7% in control area [odds ratio 0.454 (95% CI: 0.364, 0.566)]. Human \u003cem\u003eL. infantum\u003c/em\u003e infection also varied, with rates of 4% and 14.3% in the intervention and control areas, respectively. Comparing dogs and humans \u003cem\u003eL. infantum\u003c/em\u003e infections within each area, the OR of infection were 2.405 [95% CI: (1.720, 3.363) in the control area and 1.459 [(95% CI: 1.117, 1.906) in the intervention area. The pooled OR across both areas was 1.776 [95% CI: (1.441, 2.189)]. Large scale implementation of insecticide collars was effective at 6 months [ OR 0.448, 95% CI: (0.343, 0.584)], but the effect was not sustained thereafter. Nonetheless, dogs wearing collar had lower of \u003cem\u003eL. infantum\u003c/em\u003e seroconversion (p\u0026thinsp;=\u0026thinsp;0.044), and households with collared dogs had reduction in sand fly abundance. Collar coverage remained below 80%, and approximately 40% of collars were lost before the scheduled replacement at 6-month interval. Reduction in VL dog culling was observed in both areas at 6 and 12 months. Spatial analysis revealed outlier blocks of canine infection, forming clusters that influence infection dynamics in neighboring areas.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eThere was reduction in Leishmania seroconversion in dogs that used collars. The use of collars reduced sand fly density in the household. Culling of VL dogs were not systematic because of loss of follow up or non-consent from the owners.\u003c/p\u003e","manuscriptTitle":"Complexity of implementing canine visceral leishmaniasis control measures at a population level: use of impregnated deltamethrin collars and culling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-12 14:36:14","doi":"10.21203/rs.3.rs-7427065/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5b1c80ec-d75a-484b-8e63-e026876e152f","owner":[],"postedDate":"September 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T14:31:17+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-12 14:36:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7427065","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7427065","identity":"rs-7427065","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}