Serological Evidence of Lassa Virus in Commensal Rodents from Senegal.

Serological Evidence of Lassa Virus in Commensal Rodents from Senegal. | 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 Article Serological Evidence of Lassa Virus in Commensal Rodents from Senegal. Seynabou Seye, Mouhamed Kane, Safiétou Sankhe, Ndongo Dia, Gamou Fall, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7946956/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 Lassa fever, a neglected zoonotic hemorrhagic disease caused by Lassa virus (LASV) and endemic in West Africa, remains a major public health concern linked to rodent exposure. Senegal lies at the western fringe of LASV area, but only one 1988 serosurvey reported low antibody prevalence. Given recent ecological shifts, including expansion of invasive Rattus rattus and Mus musculus , we reassessed LASV exposure in domestic and peri-domestic rodents. Methods We retrospectively analyzed 618 archived rodent sera collected in 2012–2013 from domestic and peri-domestic environments in central and eastern Senegal. Samples were screened by ELISA for LASV IgG and IgM using validated Panadea assays. Spatial mapping and ecological analysis identified seropositivity clusters and potential environmental correlates. Results Eleven rodents (1.8%; 95% CI: 0.9–3.2%) were positive for LASV–specific IgG, with no IgM detected, indicating absence of acute infection. Seropositive animals occurred in five villages clustered along major transport corridors and belonged exclusively to commensal species, Rattus rattus (5%) and Mus musculus (1.1%), within low-diversity rodent communities dominated by invasive taxa. Conclusions This study provides the first update in over three decades on LASV exposure in Senegalese rodents. IgG detection confined to invasive commensal species suggests shifting reservoir dynamics, while reduced diversity at positive sites may indicate a dilution effect. Spatial clustering of seropositive rodents along major transport routes points to low-level but persistent circulation in settings favoring human–rodent contact. These findings highlight the need to integrate rodent surveillance into One Health frameworks to strengthen early warning and regional preparedness. Health sciences/Diseases Biological sciences/Ecology Earth and environmental sciences/Ecology Biological sciences/Microbiology Biological sciences/Zoology Lassa virus Rodent reservoirs Invasive species One Health surveillance Zoonotic emergence Senegal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Lassa fever is an endemic viral heamorrhagic disease in parts of West Africa and represents an important emerging infectious disease threat. Lassa fever virus (LASV) was first identified in 1969 and is classically maintained in the Natal multimammate mouse Mastomys natalensis , but accumulating field evidence shows LASV exposure in other small mammals (for example Mastomys erythroleucus, Hylomyscus pamfi, Rattus rattus , and Mus musculus ), suggesting multi-host dynamics in some contexts ( 1 ). Human infections occur primarily via rodent-to-human spillover, emphasizing the importance of rodent ecology in disease control. LASV is endemic to West Africa and causes thousands of human cases each year ( 2 ). Senegal lies at the western edge of LASV’s known distribution. Although no cases have been documented within its borders, Eastern Senegal shares frontiers with endemic areas of Mali and Guinea and is subject to regular cross-border movement of people and goods, creating opportunities for invasive species introductions and pathogen spread. Notably, previous surveys in neighboring countries have documented LASV in rodents. In Guinea, for example, seroprevalence up to 27–50% of tested M. natalensis had LASV antibodies depending of the studies ( 3 – 5 ), as well as occasional spillover to other rodent species. In southern Mali, nearly 20% of M. natalensis were LASV-positive (by antibody or antigen) and all were found in village homes ( 6 ). Similarly, recent work in Nigeria found broadly distributed LASV seroprevalence (up to ~ 50% in M. natalensis ) and even occasional positives in other species such as M. erythroleucus and R. rattus ( 7 ). In contrast, LASV has never been definitively isolated in Senegal although earlier serosurveys suggested possible exposure. A report published in 1988 described surveys of 1,440 rodents across the country, including villages where suspected cases had previously been reported ( 8 ). The study found an overall LASV antibody prevalence of 1.2%, with positives detected mainly in Mastomys spp. (2.1%), Arvicanthis niloticus (0.7%), and Mus musculus (1.4%). Since that time, ecological changes such as the inland expansion of the invasive black rat ( Rattus rattus ), may have altered the composition of potential reservoirs. To update knowledge on LASV exposure risk along the Senegalese frontier and to examine community-level correlates, we analyzed archived rodent sera collected during 2012–2013 in Senegal. Methods Archived rodent sera were retrieved from the Institut Pasteur de Dakar (IPD) biobank and screened for LASV antibodies. Rodent sampling was conducted between 2012 and 2013 in eastern Senegal, along the Tambacounda–Kédougou and Tambacounda–Kidira axes, as well as in the central region. These areas were selected because of their geographic proximity to LASV-endemic zones in Mali and Guinea and their high levels of cross-border movement and human–rodent interactions. Additional captures were also carried out in villages in Kaffrine (central Senegal) and Kaolack (west–central Senegal) to extend spatial coverage. Rodents were trapped using Sherman and locally adapted traps in domestic (inside houses) and peridomestic (surroundings of concessions) settings. Captured animals were identified to species level as previously described ( 9 ), and sera were collected and archived at − 80°C in the biobank of IPD until testing. Samples were assayed for LASV-specific IgG and IgM using Panadea Diagnostics ELISA kits (nucleoprotein antigen; Panadea Diagnostics GmbH, Hamburg, Germany) validated for rodent surveillance in West Africa ( 10 ). According to the manufacturer’s instructions, immunoreactivity values (IV) were classified as positive (IV ≥ 1.10), negative (IV ≤ 0.90), or equivocal (0.90 < IV < 1.10). Equivocal samples were retested, and IgM assays were performed only on specimens that were IgG-positive or initially equivocal. Each assay plate included manufacturer-provided controls to ensure assay validity, and experimental runs that failed to meet quality-control criteria were systematically repeated. Species counts and prevalence estimates were generated with 95% confidence intervals (CIs) calculated using the exact Clopper–Pearson method. Shannon diversity indices (H′) were derived from species counts for each site, and diversity was compared between LASV-seropositive and LASV-seronegative localities using the Mann–Whitney U test. Associations between species identity and LASV seropositivity were examined with Fisher’s exact test, with odds ratios (ORs) and exact p-values reported. Results A total of 618 archived sera were found. The geographic distribution of sampling sites is shown in Fig. 1 . Collection localities were spread across central and southeastern Senegal, with sites in Kaffrine (Niahène and Ida Seco) and Kaolack (Gandiaye) as well as in Tambacounda, Kédougou (Kedougou, Segou, Mako) and Kolda(Velingara, Sintian koudara and Kounkane). They cluster specifically around transport corridors. The map highlights the wide coverage of the survey, spanning both central regions and border areas close to Mali and Guinea, where cross-border movement and human–rodent interactions are frequent. Most sera originated from eastern Senegalese localities situated along the trans-Sahelian road near the Malian border, with Youppe Hamady (48/618; 7.8%), Kothiary (47/618; 7.6%), Dianké Makha (46/618; 7.4%), Kidira (45/618; 7.3%), and Bala (44/618; 7.1%) together accounting for nearly 37% of all samples. These eastern sites were sampled across both rainy and dry seasons, capturing contrasting ecological contexts and periods of rodent activity. Additional contributions came from central Senegal, particularly the Kaffrine villages of Niahène (34/618), and Ida Seco (28/618), as well as Gandiaye (29/618) in Kaolack, during the same seasonal campaigns. In contrast, fewer samples were obtained from more peripheral southeastern sites such as Kounkane, Kedougou, and Mako. Thus, our dataset reflects stronger representation of roadside and cross-border hubs compared with more remote areas, while spanning both wet- and dry-season conditions (see figure S1 ). A total of ten taxa were identified among the 618 individuals captured. Commensal species were most abundant, with Rattus rattus (n = 180; 29.1%) and Mus musculus (n = 174; 28.2%) together comprising over half of all captures (figure S2 ), followed by Crocidura spp. (n = 137; 22.2%). Other species such as Arvicanthis niloticus (n = 53; 8.6%), Mastomys erythroleucus (n = 35; 5.7%), Praomys daltoni (n = 24; 3.7%) and Mastomys natalensis (n = 11; 1,8%) occurred at lower frequencies, while additional taxa ( Steatomys sp., Nannomys , Gerbilliscus gambianus ) were only sporadically detected. R. rattus was widely distributed, with higher numbers recorded in Goumbayel, Dianké Makha, Gouloumbou and Dide Gassama, while M. musculus showed a similarly broad distribution, particularly in Mbirkilane, Sinthiou Malème, Goudiri, Niahène (Fig. 2 ). By contrast, Mastomys natalensis was rare and detected only in the southeastern sites: Kédougou, Mako and Segou. Overall, R. rattus and M. musculus were dominant and widespread, especially in roadside villages, whereas recognized LASV reservoir species were found only occasionally and in low numbers. Sex ratios varied across species captured (figure S3 ). Rattus rattus (57.5% females) and Mus musculus (59.8% females) showed significant female bias, while Crocidura sp., Arvicanthis niloticus , M. erythroleucus , and M. natalensis displayed more balanced distributions. Praomys daltoni also showed a female predominance (68.2%), whereas rare taxa ( Gerbilliscus gambianus , Nannomys , Steatomys sp.) were represented by very few individuals, limiting interpretation. Of the 618 sera tested, 11 (1.8%; 95% CI: 0.9–3.2%) were positive for LASV-specific IgG (Table 1 ). All seropositive samples originated from commensal species, namely Rattus rattus (9/180; 5%) and Mus musculus (2/174; 1.1%). No IgM antibodies were detected, indicating an absence of acute infections among the archived specimens. Table 1 Summary statistics of LASV IgG ELISA results in rodents from Senegal (2012–2013). Descriptive statistics of LASV IgG ELISA index values (IVsample​ value) according to serological status. Among 618 sera tested, 11 (1.8%; 95% CI: 0.9–3.2%) were positive for LASV-specific IgG, all from commensal species, Rattus rattus (5%) and Mus musculus (1.1%). No IgM antibodies were detected, indicating no evidence of acute infection in the archived specimens. Serological status n Mean (IVsample) Standard deviation Median Min. (IVsample) Max. (IVsample) Equivocal 3 0.944 0.045 0.942 0.901 0.991 Negative 604 0.285 0.114 0.254 0.112 0.891 Positive 11 1.934 0.949 1.470 1.124 3.816 Seropositive samples were geographically clustered in five villages located along major transport and border corridors (Fig. 3 ). The corresponding IVsample values for positive specimens ranged from approximately 1.12 to 3.82 (mean = 1.93 ± 0.95) (Table 1 , figure S4 ). Three additional sera (0.5%) yielded equivocal results (mean IVsample value = 0.944 ± 0.045), indicating sporadic intermediate antibody reactivity. These were detected in Arvicanthis niloticus from Ida Seco and in Mus musculus from Gandiaye and Kidira. Statistical comparisons between exposed species were performed using the Mann–Whitney U test to evaluate differences in LASV-specific IgG responses (Fig. 4 A). Although Rattus rattus exhibited a trend toward broader and stronger immune responses compared to Mus musculus (mean IVsample: 2.09 ± 0.99 vs. 1.23 ± 0.15), this difference did not reach statistical significance (p > 0.05). These findings suggest that the two species may experience comparable levels of exposure or susceptibility, although interpretation is limited by the small sample size, particularly for M. musculus . Spatial analysis further indicated that several individuals from Didé Gassama displayed particularly high immune responses (mean IVsample: 2.66 ± 1.00) relative to individuals from other localities. However, these geographic differences were also not statistically significant (p > 0.05; Fig. 4 B). (B) Spatial variation in IgG responses across LASV-seropositive localities. Individuals from Didé Gassama exhibited the highest mean IgG values (2.66 ± 1.00), but no significant differences were observed among sites ( p > 0.05). The dashed red line represents the positive threshold (IVsample_{sample}sample​ = 1.1). At the site level, mean Shannon diversity was lower in LASV-positive localities (H′ ≈ 0.35) than in LASV-negative localities (H′ ≈ 0.70), suggesting a tendency toward reduced species diversity where LASV exposure was detected. This pattern was also apparent in the diversity–positivity scatterplot, where a weak negative correlation was observed (r = − 0.21, R² = 0.044). However, neither the Mann–Whitney U test (p = 0.14) nor the correlation analysis (p = 0.093) reached statistical significance, indicating that the association between species diversity and LASV seropositivity remains suggestive but inconclusive (Fig. 5 ). Discussion Our results indicate that, in addition to Mastomys natalensis , commensal rodents such as the black rat R. rattus and the house mouse M. musculus can play a role in LASV exposure. Field surveys in Nigeria found R. rattus and M. musculus constituted large fractions of captured rodents, and both species tested positive for LASV by PCR. For example, Agbonlahor et al. reported that M. musculus (39.4%) and R. rattus (36.1%) were the dominant species in rodent collections, and PCR-detected LASV in all three of these (and M. natalensis ) in LASV-endemic states ( 11 ). Similarly, Happi et al. found all captured rodent genera (including Rattus and Mus ) had LASV positivity, with Rattus spp. having the highest infection rate (77.3% in Ondo State, Nigeria) compared to 41.6% for Mastomys spp. in Ebonyi State ( 12 ). Our detection of LASV IgG in Rattus and Mus from Senegal aligns with these regional findings, suggesting that multiple commensal species may contribute to arenavirus exposure patterns in domestic settings ( 7 , 13 , 14 ). Our data confirm that non- Mastomys synanthropes in West Africa can harbor LASV, underscoring their potential as secondary reservoirs or as part of complex transmission webs. Recent ecological studies in Senegal further confirm that R. rattus and M. musculus dominate commensal rodent communities in many villages, often displacing native M. natalensis ( 15 ). Such displacement can alter community structure and potentially reshape LASV transmission dynamics. In our study, LASV-positive sites showed lower mean Shannon diversity than negative sites, a trend consistent with simplified communities dominated by invasive commensals potentially altering LASV exposure dynamics, although this association did not reach statistical significance. The role of invasive commensals is nuanced. On one hand, increased rodent biodiversity, particularly replacement of the primary reservoir, could dilute LASV transmission. Historical data from Guinea show that coastal regions dominated by introduced R. rattus and M. musculus had low human Lassa seroprevalence, whereas inland areas with many M. natalensis had high LASV antibody rates. Fichet-Calvet et al. found a negative relationship between non-native rodents and Lassa risk: prefectures where M. musculus predominated (and M. natalensis was scarce) unexpectedly had low Lassa antibody prevalence in people ( 16 ). More recently, Eskew et al. showed that invasion by R. rattus in Sierra Leone/Guinea strongly depressed M. natalensis house density and correlated with reduced LASV spillover risk ( 1 ). In other words, invasive R. rattus appear to have an indirect “dilution” effect by outcompeting the primary reservoir in domestic settings. On the other hand, invasive commensals themselves may become LASV sources. The Nigerian surveys above demonstrate that R. rattus and M. musculus can carry LASV at rates comparable to or exceeding Mastomys . In Ondo State, Rattus spp. had 77% LASV positivity versus 41% in Mastomys ( 12 ). This implies that under certain ecological or anthropogenic contexts such as high rodent density in trade hubs, non-native species could act as amplifying hosts or bridge species between wildlife and humans. Likewise, experimental and genetic studies suggest that newly invasive M. musculus encounters high parasite pressure in Senegal: immune gene expression was elevated in house mice at recent invasion fronts, hinting at increased infection risk when M. musculus colonizes new areas ( 17 ). Together, these findings reveal a dual ecological reality: invasion may suppress traditional reservoirs yet simultaneously open new niches for viral maintenance. The net epidemiological outcome depends on local community composition, land-use patterns, and human–rodent contact frequency. Environmental and seasonal dynamics further modulate LASV risk across West Africa. Climatic and ecological changes are predicted to alter Mastomys demography and thus human risk. Modeling of Mastomys in West Africa suggests that shifts in the timing or synchrony of the rodent breeding season (driven by climate or land-use change) would change the peak of LASV prevalence in rodents, and hence the timing of human risk ( 18 ). Empirical incidence data in Nigeria support a strong seasonality: spillover to humans surges in the dry season (December–March), coinciding with peak rodent population fluctuations ( 19 ). These ecological insights reinforce that Lassa virus circulation is dynamic, responsive to both natural and anthropogenic pressures. Our study has limitations that must be acknowledged. Because our rodent data were retrospective and based on serology, we cannot confirm active LASV infection or identify viral lineages. Future efforts combining molecular detection, viral sequencing, and ecological metadata are needed to clarify the genetic diversity and temporal dynamics of LASV in Senegal. Additionally, the cross-sectional design cannot capture seasonal fluctuations or direct transmission chains. Nevertheless, strengths include use of a high-specificity ELISA validated for LASV IgG detection, a relatively large geographic coverage, and rigorous species identification. These provide a valuable baseline for integrating rodent surveillance into broader One Health monitoring frameworks. From a public-health and One Health perspective, our findings have several implications. First, the detection of LASV antibodies in Senegalese rodents extends the known ecological range of the virus and underscores the need to maintain vigilance in regions previously considered non-endemic. Integrating animal surveillance within existing national systems would enable early detection of silent circulation. Second, collaboration with regional and international bodies such as the West African Health Organization (WAHO), the World Health Organization (WHO), Africa CDC, and the World Organisation for Animal Health (WOAH) could help harmonize cross-border animal and human surveillance systems. Coordinated serological and genomic monitoring of rodents and other reservoirs would strengthen One Health preparedness for emerging zoonoses in West Africa. Third, linking environmental monitoring, community education, and rodent-control interventions to socioeconomic indicators could mitigate poverty-related exposure risks. Ultimately, our findings highlight important One Health implications. They suggest that LASV prevention requires integrated surveillance across wildlife, domestic animals and human health sectors. Past reviews emphasize that intensifying interdisciplinary (One Health) efforts is essential to improve LASV surveillance and control in West Africa ( 20 ). In practical terms, this means combining rodent ecology monitoring (including both native and invasive species) with human case surveillance. For public health, understanding where non- Mastomys rodents flourish, and how seasonal or environmental changes affect them, can help target interventions (e.g. seasonal sanitation or rodent control) to reduce spillover. Controlling Lassa fever in Senegal and the region will require a coordinated strategy that accounts for shifts in rodent community composition, invasion dynamics, and seasonal ecology. Such a One Health approach, linking animal reservoir studies with clinical surveillance, will be critical to anticipate and mitigate LASV emergence in human populations. Declarations Acknowledgments We gratefully acknowledge Laurent Granjon, Christophe Amidi Diagne, and the CBGP teams of the Institut de Recherche pour le Développement (IRD) in Montpellier (France) and Dakar (Senegal) for their exceptional contributions to the rodent trapping efforts. We also thank Pascal Handschumacher, principal investigator of the CHANCIRA project, for his valuable support. Funding Fieldwork and samples archiving were supported by the Agence Nationale de la Recherche (ANR) through the CHANCIRA project (ANR-11-CEPL-010). Laboratory investigations were funded by internal resources of the Institut Pasteur de Dakar. The authors declare that no author received any payment or financial support from pharmaceutical companies or external agencies for the preparation of this manuscript. The corresponding author affirms that all authors had full access to the data and accept responsibility for the decision to submit the manuscript for publication. Clinical trial number: Not applicable. Conflicts of Interest The authors declare no competing interests. Data Availability The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request. Author Contributions: S.S. and M.K. performed the laboratory experiments, curated the data, and contributed to the formal analysis. S.Sa. supervised and validated the experimental work. N.D., G.F., O.F., and M.Di. provided resources, while M.Di., N.D., and M.M.D. secured funding. The study was conceptualized by A.G. and M.M.D. M.M.D. also performed the formal analysis, prepared the figures, and managed project administration. S.S., A.G., and M.M.D. wrote the main manuscript text. All authors reviewed and approved the final version of the manuscript. References Eskew, E. A. et al. Reservoir displacement by an invasive rodent reduces Lassa virus zoonotic spillover risk. Nat. Commun. 15 (1), 3589 (2024). Ogundele, G. O., Jolayemi, K. O. & Bello, S. Lassa fever in West Africa: a systematic review and meta-analysis of attack rates, case fatality rates and risk factors. BMC Public. Health . 25 (1), 2948 (2025). Demby, A. H. et al. Lassa Fever in Guinea: II. Distribution and Prevalence of Lassa Virus Infection in Small Mammals. Vector-Borne Zoonotic Dis. 1 (4), 283–297 (2001). Fichet-Calvet, E. et al. Fluctuation of Abundance and Lassa Virus Prevalence in Mastomys natalensis in Guinea, West Africa. Vector-Borne Zoonotic Dis. 7 (2), 119–128 (2007 June). Fichet-Calvet, E., Becker-Ziaja, B., Koivogui, L. & Günther, S. Lassa Serology in Natural Populations of Rodents and Horizontal Transmission. Vector Borne Zoonotic Dis. Sept 1;14(9):665–74. (2014). Safronetz, D. et al. Geographic Distribution and Genetic Characterization of Lassa Virus in Sub-Saharan Mali. PLoS Negl. Trop. Dis. 7 (12), e2582 (2013). Olayemi, A. et al. Widespread arenavirus occurrence and seroprevalence in small mammals, Nigeria. Parasit. Vectors 2018 July 13 ;11(1):416 . Saluzzo, J. F., Adam, F., McCormick, J. B. & Digoutte, J. P. Lassa fever virus in Senegal. J. Infect. Dis. 157 (3), 605 (1988). Dalecky, A. et al. Range expansion of the invasive house mouse Mus musculus domesticus in Senegal, West Africa: a synthesis of trapping data over three decades, 1983–2014. Mammal Rev. 45 (3), 176–190 (2015). Soubrier, H. et al. Detection of Lassa Virus-Reactive IgG Antibodies in Wild Rodents: Validation of a Capture Enzyme-Linked Immunological Assay. Viruses 14 (5), 993 (2022). Agbonlahor, D. E. et al. Prevalence of Lassa virus among rodents trapped in three South-South States of Nigeria. J. Vector Borne Dis. 54 (2), 146–150 (2017). Happi, A. N. et al. Increased Prevalence of Lassa Fever Virus-Positive Rodents and Diversity of Infected Species Found during Human Lassa Fever Epidemics in Nigeria. Microbiol. Spectr. 10 (4), e00366–e00322 (2022). Fichet-Calvet, E. & Rogers, D. J. Risk maps of Lassa fever in West Africa. PLoS Negl. Trop. Dis. 3 (3), e388 (2009). Hastie, K. M. et al. The Arenaviridae Family: Knowledge Gaps, Animal Models, Countermeasures, and Prototype Pathogens. J. Infect. Dis. 228 (Suppl 6), S359–S375 (2023). Granjon, L. et al. Sharing space between native and invasive small mammals: Study of commensal communities in Senegal. Ecol. Evol. 20 (9), e10539 (2023 Sept). Fichet-Calvet, E. et al. Spatial distribution of commensal rodents in regions with high and low Lassa fever prevalence in Guinea. Belg. J. Zool. 135 , 63–67 (2005). Charbonnel, N. et al. Differential immune gene expression associated with contemporary range expansion in two invasive rodents in Senegal. Sci. Rep. 10 (1), 18257 (2020). John, R. S., Fatoyinbo, H. O. & Hayman, D. T. S. Modelling Lassa virus dynamics in West African Mastomys natalensis and the impact of human activities. J R Soc Interface. July 24;21(216):20240106. (2024). McKendrick, J. Q., Tennant, W. S. D. & Tildesley, M. J. Modelling seasonality of Lassa fever incidences and vector dynamics in Nigeria. PLoS Negl. Trop. Dis. 17 (11), e0011543 (2023). Arruda, L. B. et al. The niche of One Health approaches in Lassa fever surveillance and control. Ann. Clin. Microbiol. Antimicrob. 20 (1), 29 (2021). Additional Declarations No competing interests reported. Supplementary Files FigureS1.png Figure S1. Distribution of rodent captures by locality and sampling period (Senegal, 2012–2013). Bar chart showing the number of individuals captured per site (n = 618), colored by sampling period. The highest sampling intensity occurred in eastern Senegal (Youppe Hamady, Kothiary, Dianké Makha, Kidira, Bala), which together accounted for nearly 37 % of all samples, followed by central sites in Kaffrine (Niahène, Ida Seco) and Kaolack (Gandiaye). Southeastern localities such as Kounkane, Kédougou, and Mako were less represented. Sampling spanned both rainy and dry seasons, capturing ecological contrasts along the trans-Sahelian corridor. FigureS2.png Figure S2. Species composition of rodents captured in Senegal (2012–2013). Bar plot showing the relative percentage of captured individuals by species (n = 618). Commensal species ( Rattus rattus , 29.1 %; Mus musculus , 28.2 %) together accounted for more than half of all captures, followed by Crocidura spp. (22.2 %). Other taxa, including Arvicanthis niloticus , Mastomys erythroleucus , Praomys daltoni , and Mastomys natalensis —were present at lower frequencies, while Steatomys sp., Nannomys , and Gerbilliscus gambianus were rarely detected. Error bars represent standard errors of the mean across sampling localities. FigureS3.png Figure S3. Sex ratio by species among captured rodents (Senegal, 2012–2013). Stacked bar chart showing the number and proportion of males (blue) and females (pink) within each species. Asterisks denote species with significant female bias ( p < 0.05). Rattus rattus and Mus musculus exhibited marked female predominance, whereas Crocidura sp. , Arvicanthis niloticus , Mastomys erythroleucus , and Mastomys natalensis showed near-balanced sex ratios. Other species were captured in too few numbers for meaningful statistical comparison. FigureS4.png Figure S4. Distribution of LASV IgG ELISA results across qualitative categories. Violin plot showing the distribution of individual IVsample values according to qualitative ELISA outcomes (negative, equivocal, and positive). Dashed orange lines indicate assay cut-off thresholds (0.9 for negative and 1.1 for positive). Most samples fell within the negative range (n = 604), whereas 11 samples exceeded the positive threshold (IVsample_{sample}sample​ ≈ 1.12–3.82; mean = 1.93 ± 0.95), and three were classified as equivocal (mean = 0.944 ± 0.045). Shaded background zones delineate interpretation ranges defined by the Panadea Diagnostics ELISA protocol. 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. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7946956","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":555069912,"identity":"97cf3c21-c5c1-4019-b5f5-21c5347f43d3","order_by":0,"name":"Seynabou Seye","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Seynabou","middleName":"","lastName":"Seye","suffix":""},{"id":555069913,"identity":"bac50925-b3ce-41a4-89c2-a5cd2fdcf593","order_by":1,"name":"Mouhamed Kane","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Mouhamed","middleName":"","lastName":"Kane","suffix":""},{"id":555069914,"identity":"d32533a2-5d4d-480d-9690-4f00df1aab7b","order_by":2,"name":"Safiétou Sankhe","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Safiétou","middleName":"","lastName":"Sankhe","suffix":""},{"id":555069915,"identity":"d635ede0-90bc-4bd3-a509-9542c6df054e","order_by":3,"name":"Ndongo Dia","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Ndongo","middleName":"","lastName":"Dia","suffix":""},{"id":555069916,"identity":"49b7bfe1-5db5-4ad9-9e79-b94cdd816eca","order_by":4,"name":"Gamou Fall","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Gamou","middleName":"","lastName":"Fall","suffix":""},{"id":555069917,"identity":"3f7f5a6d-c390-44fe-89b0-24b6c75a3c9d","order_by":5,"name":"Oumar Faye","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Oumar","middleName":"","lastName":"Faye","suffix":""},{"id":555069918,"identity":"7fc99f3a-c6df-4eed-87e8-93a5e209f825","order_by":6,"name":"Mawlouth Diallo","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Mawlouth","middleName":"","lastName":"Diallo","suffix":""},{"id":555069919,"identity":"6b350e78-c2c6-416d-acf9-a9c6c4229d38","order_by":7,"name":"Alioune Gaye","email":"","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":false,"prefix":"","firstName":"Alioune","middleName":"","lastName":"Gaye","suffix":""},{"id":555069920,"identity":"30f4d4be-4429-4b04-b2ed-25c00363c461","order_by":8,"name":"Moussa Moise Diagne","email":"data:image/png;base64,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","orcid":"","institution":"Institut Pasteur de Dakar","correspondingAuthor":true,"prefix":"","firstName":"Moussa","middleName":"Moise","lastName":"Diagne","suffix":""}],"badges":[],"createdAt":"2025-10-27 10:47:46","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7946956/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7946956/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":97497331,"identity":"1fdad91a-9b3c-4653-a2db-e4ff0845f173","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":512821,"visible":true,"origin":"","legend":"\u003cp\u003eGeographic distribution of rodent sampling sites in Senegal (2012–2013). Map showing the 29 localities where rodents were trapped for LASV serological screening. Sampling sites (red dots) were distributed across eastern, central, and southeastern Senegal, with higher density along the trans-Sahelian road near the Malian border. The inset highlights the eastern corridor (Tambacounda–Kédougou axis), where most captures occurred in roadside and cross-border villages.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/f2709288743629433c3f39d1.png"},{"id":97669427,"identity":"269d8904-b272-49fc-aea3-dfea9e2bb24b","added_by":"auto","created_at":"2025-12-08 09:27:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":147959,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDistribution of captured rodent species across collection sites in Senegal (2012–2013). \u003c/strong\u003eHeatmap showing the number of individuals captured per species and locality. \u003cem\u003eRattus rattus\u003c/em\u003e and \u003cem\u003eMus musculus\u003c/em\u003ewere the most abundant and widely distributed species, particularly in roadside and cross-border villages such as Goumbayel, Dianké Makha, Gouloumbou, Didé Gassama, Mbirkilane, Sinthiou Malème, Goudiri, and Niahène. In contrast, \u003cem\u003eMastomys natalensis\u003c/em\u003e—the recognized LASV reservoir—was rare and found only in southeastern sites (Kédougou, Mako, and Ségou). Overall, invasive commensal species dominated rodent communities, while native reservoirs occurred sporadically and in low numbers.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/b4e71f040efd14e479f8cc68.png"},{"id":97669935,"identity":"3901b5f0-7aa2-4d92-bc52-1f3e49b9d5bb","added_by":"auto","created_at":"2025-12-08 09:29:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":120877,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial distribution of LASV IgG–positive and equivocal rodent samples in Senegal (2012–2013). Map showing the geographic locations of LASV-seropositive (red) and equivocal (green) samples detected among rodents. Seropositive cases were geographically clustered in five villages located along major transport and border corridors, primarily Didé Gassama, Sinthiou Koudara, Niahène, Sinthiou Malème, and Kounkane, while equivocal samples were identified in \u003cem\u003eArvicanthis niloticus\u003c/em\u003e from Ida Seco and in \u003cem\u003eMus musculus\u003c/em\u003e from Gandiaye and Kidira. The pattern highlights a focal distribution of LASV antibody detection along high-connectivity routes linking eastern and central Senegal.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/fec4ba9544373e56ae62c848.png"},{"id":97497338,"identity":"b2c8f0bb-62cb-44ee-a0dc-71ddafe1dd6e","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":245305,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of LASV-specific IgG responses by species and locality. (A)\u003c/strong\u003eDistribution of LASV IgG index values in \u003cem\u003eRattus rattus\u003c/em\u003e and \u003cem\u003eMus musculus\u003c/em\u003e based on ELISA results. Although \u003cem\u003eR. rattus\u003c/em\u003e showed a trend toward higher antibody levels (mean IVsample_{sample}sample​: 2.09 ± 0.99) compared to \u003cem\u003eM. musculus\u003c/em\u003e (1.23 ± 0.15), the difference was not statistically significant (Mann–Whitney U test, \u003cem\u003ep\u003c/em\u003e \u0026gt; 0.05).\u003cbr\u003e\n \u003cstrong\u003e(B)\u003c/strong\u003e Spatial variation in IgG responses across LASV-seropositive localities. Individuals from Didé Gassama exhibited the highest mean IgG values (2.66 ± 1.00), but no significant differences were observed among sites (\u003cem\u003ep\u003c/em\u003e \u0026gt; 0.05). The dashed red line represents the positive threshold (IVsample_{sample}sample​ = 1.1).\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/d35dd64c807eacf279248c9d.png"},{"id":97497337,"identity":"a53e9b7a-f0c5-432e-a471-c69d617268fe","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":366395,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRelationship between rodent community diversity and LASV seropositivity across sampling sites. \u003c/strong\u003eScatterplot showing the relationship between Shannon’s diversity index (H′) and LASV IgG positivity rate across 29 localities. LASV-positive sites exhibited lower mean diversity (H′ ≈ 0.35) compared to negative sites (H′ ≈ 0.70). A weak negative correlation was observed (r = –0.21, R² = 0.044), suggesting a tendency toward reduced species diversity in LASV-exposed communities. However, neither the Mann–Whitney U test (\u003cem\u003ep\u003c/em\u003e = 0.14) nor correlation analysis (\u003cem\u003ep\u003c/em\u003e = 0.093) reached statistical significance.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/09b5e4ff58892e6479ff2ac3.png"},{"id":98421088,"identity":"386d407b-33dd-49e8-adba-d5308d804f6b","added_by":"auto","created_at":"2025-12-17 16:23:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1859789,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/d6da282c-f370-48a1-840a-d99a983e666f.pdf"},{"id":97670936,"identity":"df83ef5c-e400-44d8-ae1f-7a32b5466db4","added_by":"auto","created_at":"2025-12-08 09:31:33","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":128592,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure S1. Distribution of rodent captures by locality and sampling period (Senegal, 2012–2013).\u003c/strong\u003e Bar chart showing the number of individuals captured per site (n = 618), colored by sampling period. The highest sampling intensity occurred in eastern Senegal (Youppe Hamady, Kothiary, Dianké Makha, Kidira, Bala), which together accounted for nearly 37 % of all samples, followed by central sites in Kaffrine (Niahène, Ida Seco) and Kaolack (Gandiaye). Southeastern localities such as Kounkane, Kédougou, and Mako were less represented. Sampling spanned both rainy and dry seasons, capturing ecological contrasts along the trans-Sahelian corridor.\u003c/p\u003e","description":"","filename":"FigureS1.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/78846902363b2cfccd77a71c.png"},{"id":97497335,"identity":"5238f2a8-ed45-48c3-afa7-adb76f6a2377","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":348170,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure S2. Species composition of rodents captured in Senegal (2012–2013).\u003c/strong\u003e\u003cbr\u003e\nBar plot showing the relative percentage of captured individuals by species (n = 618). Commensal species (\u003cem\u003eRattus rattus\u003c/em\u003e, 29.1 %; \u003cem\u003eMus musculus\u003c/em\u003e, 28.2 %) together accounted for more than half of all captures, followed by \u003cem\u003eCrocidura\u003c/em\u003espp. (22.2 %). Other taxa, including \u003cem\u003eArvicanthis niloticus\u003c/em\u003e, \u003cem\u003eMastomys erythroleucus\u003c/em\u003e, \u003cem\u003ePraomys daltoni\u003c/em\u003e, and \u003cem\u003eMastomys natalensis\u003c/em\u003e—were present at lower frequencies, while \u003cem\u003eSteatomys\u003c/em\u003e sp., \u003cem\u003eNannomys\u003c/em\u003e, and \u003cem\u003eGerbilliscus gambianus\u003c/em\u003e were rarely detected. Error bars represent standard errors of the mean across sampling localities.\u003c/p\u003e","description":"","filename":"FigureS2.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/fdd3c988f323a0043f9d6dd2.png"},{"id":97497339,"identity":"7853c640-5f8f-48e7-9ab1-e05b68f57d73","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":488281,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure S3. Sex ratio by species among captured rodents (Senegal, 2012–2013).\u003c/strong\u003e\u003cbr\u003e\nStacked bar chart showing the number and proportion of males (blue) and females (pink) within each species. Asterisks denote species with significant female bias (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05). \u003cem\u003eRattus rattus\u003c/em\u003e and \u003cem\u003eMus musculus\u003c/em\u003eexhibited marked female predominance, whereas \u003cem\u003eCrocidura sp.\u003c/em\u003e, \u003cem\u003eArvicanthis niloticus\u003c/em\u003e, \u003cem\u003eMastomys erythroleucus\u003c/em\u003e, and \u003cem\u003eMastomys natalensis\u003c/em\u003eshowed near-balanced sex ratios. Other species were captured in too few numbers for meaningful statistical comparison.\u003c/p\u003e","description":"","filename":"FigureS3.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/a10bd3c3e4f3aebf5512ccd1.png"},{"id":97497333,"identity":"11d4d378-f795-480c-bf44-c0413edf120e","added_by":"auto","created_at":"2025-12-05 05:03:24","extension":"png","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":295097,"visible":true,"origin":"","legend":"\u003cp\u003eFigure S4. Distribution of LASV IgG ELISA results across qualitative categories. Violin plot showing the distribution of individual IVsample values according to qualitative ELISA outcomes (negative, equivocal, and positive). Dashed orange lines indicate assay cut-off thresholds (0.9 for negative and 1.1 for positive). Most samples fell within the negative range (n = 604), whereas 11 samples exceeded the positive threshold (IVsample_{sample}sample​ ≈ 1.12–3.82; mean = 1.93 ± 0.95), and three were classified as equivocal (mean = 0.944 ± 0.045). Shaded background zones delineate interpretation ranges defined by the Panadea Diagnostics ELISA protocol.\u003c/p\u003e","description":"","filename":"FigureS4.png","url":"https://assets-eu.researchsquare.com/files/rs-7946956/v1/b80e7037d3c9a82d4f42ac7b.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSerological Evidence of Lassa Virus in Commensal Rodents from Senegal.\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLassa fever is an endemic viral heamorrhagic disease in parts of West Africa and represents an important emerging infectious disease threat. Lassa fever virus (LASV) was first identified in 1969 and is classically maintained in the Natal multimammate mouse \u003cem\u003eMastomys natalensis\u003c/em\u003e, but accumulating field evidence shows LASV exposure in other small mammals (for example \u003cem\u003eMastomys erythroleucus, Hylomyscus pamfi, Rattus rattus\u003c/em\u003e, and \u003cem\u003eMus musculus\u003c/em\u003e), suggesting multi-host dynamics in some contexts (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). Human infections occur primarily via rodent-to-human spillover, emphasizing the importance of rodent ecology in disease control. LASV is endemic to West Africa and causes thousands of human cases each year (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSenegal lies at the western edge of LASV\u0026rsquo;s known distribution. Although no cases have been documented within its borders, Eastern Senegal shares frontiers with endemic areas of Mali and Guinea and is subject to regular cross-border movement of people and goods, creating opportunities for invasive species introductions and pathogen spread.\u003c/p\u003e\u003cp\u003eNotably, previous surveys in neighboring countries have documented LASV in rodents. In Guinea, for example, seroprevalence up to 27\u0026ndash;50% of tested \u003cem\u003eM. natalensis\u003c/em\u003e had LASV antibodies depending of the studies (\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), as well as occasional spillover to other rodent species. In southern Mali, nearly 20% of \u003cem\u003eM. natalensis\u003c/em\u003e were LASV-positive (by antibody or antigen) and all were found in village homes (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). Similarly, recent work in Nigeria found broadly distributed LASV seroprevalence (up to ~\u0026thinsp;50% in \u003cem\u003eM. natalensis\u003c/em\u003e) and even occasional positives in other species such as \u003cem\u003eM. erythroleucus\u003c/em\u003e and \u003cem\u003eR. rattus\u003c/em\u003e (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn contrast, LASV has never been definitively isolated in Senegal although earlier serosurveys suggested possible exposure. A report published in 1988 described surveys of 1,440 rodents across the country, including villages where suspected cases had previously been reported (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). The study found an overall LASV antibody prevalence of 1.2%, with positives detected mainly in \u003cem\u003eMastomys\u003c/em\u003e spp. (2.1%), \u003cem\u003eArvicanthis niloticus\u003c/em\u003e (0.7%), and \u003cem\u003eMus musculus\u003c/em\u003e (1.4%). Since that time, ecological changes such as the inland expansion of the invasive black rat (\u003cem\u003eRattus rattus\u003c/em\u003e), may have altered the composition of potential reservoirs. To update knowledge on LASV exposure risk along the Senegalese frontier and to examine community-level correlates, we analyzed archived rodent sera collected during 2012\u0026ndash;2013 in Senegal.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eArchived rodent sera were retrieved from the Institut Pasteur de Dakar (IPD) biobank and screened for LASV antibodies. Rodent sampling was conducted between 2012 and 2013 in eastern Senegal, along the Tambacounda\u0026ndash;K\u0026eacute;dougou and Tambacounda\u0026ndash;Kidira axes, as well as in the central region. These areas were selected because of their geographic proximity to LASV-endemic zones in Mali and Guinea and their high levels of cross-border movement and human\u0026ndash;rodent interactions. Additional captures were also carried out in villages in Kaffrine (central Senegal) and Kaolack (west\u0026ndash;central Senegal) to extend spatial coverage. Rodents were trapped using Sherman and locally adapted traps in domestic (inside houses) and peridomestic (surroundings of concessions) settings. Captured animals were identified to species level as previously described (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e), and sera were collected and archived at \u0026minus;\u0026thinsp;80\u0026deg;C in the biobank of IPD until testing.\u003c/p\u003e\u003cp\u003eSamples were assayed for LASV-specific IgG and IgM using Panadea Diagnostics ELISA kits (nucleoprotein antigen; Panadea Diagnostics GmbH, Hamburg, Germany) validated for rodent surveillance in West Africa (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). According to the manufacturer\u0026rsquo;s instructions, immunoreactivity values (IV) were classified as positive (IV\u0026thinsp;\u0026ge;\u0026thinsp;1.10), negative (IV\u0026thinsp;\u0026le;\u0026thinsp;0.90), or equivocal (0.90\u0026thinsp;\u0026lt;\u0026thinsp;IV\u0026thinsp;\u0026lt;\u0026thinsp;1.10). Equivocal samples were retested, and IgM assays were performed only on specimens that were IgG-positive or initially equivocal. Each assay plate included manufacturer-provided controls to ensure assay validity, and experimental runs that failed to meet quality-control criteria were systematically repeated.\u003c/p\u003e\u003cp\u003eSpecies counts and prevalence estimates were generated with 95% confidence intervals (CIs) calculated using the exact Clopper\u0026ndash;Pearson method. Shannon diversity indices (H\u0026prime;) were derived from species counts for each site, and diversity was compared between LASV-seropositive and LASV-seronegative localities using the Mann\u0026ndash;Whitney U test. Associations between species identity and LASV seropositivity were examined with Fisher\u0026rsquo;s exact test, with odds ratios (ORs) and exact p-values reported.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 618 archived sera were found. The geographic distribution of sampling sites is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eCollection localities were spread across central and southeastern Senegal, with sites in Kaffrine (Niah\u0026egrave;ne and Ida Seco) and Kaolack (Gandiaye) as well as in Tambacounda, K\u0026eacute;dougou (Kedougou, Segou, Mako) and Kolda(Velingara, Sintian koudara and Kounkane). They cluster specifically around transport corridors. The map highlights the wide coverage of the survey, spanning both central regions and border areas close to Mali and Guinea, where cross-border movement and human\u0026ndash;rodent interactions are frequent.\u003c/p\u003e\u003cp\u003eMost sera originated from eastern Senegalese localities situated along the trans-Sahelian road near the Malian border, with Youppe Hamady (48/618; 7.8%), Kothiary (47/618; 7.6%), Diank\u0026eacute; Makha (46/618; 7.4%), Kidira (45/618; 7.3%), and Bala (44/618; 7.1%) together accounting for nearly 37% of all samples. These eastern sites were sampled across both rainy and dry seasons, capturing contrasting ecological contexts and periods of rodent activity. Additional contributions came from central Senegal, particularly the Kaffrine villages of Niah\u0026egrave;ne (34/618), and Ida Seco (28/618), as well as Gandiaye (29/618) in Kaolack, during the same seasonal campaigns. In contrast, fewer samples were obtained from more peripheral southeastern sites such as Kounkane, Kedougou, and Mako. Thus, our dataset reflects stronger representation of roadside and cross-border hubs compared with more remote areas, while spanning both wet- and dry-season conditions (see figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eA total of ten taxa were identified among the 618 individuals captured. Commensal species were most abundant, with \u003cem\u003eRattus rattus\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;180; 29.1%) and \u003cem\u003eMus musculus\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;174; 28.2%) together comprising over half of all captures (figure \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e), followed by \u003cem\u003eCrocidura\u003c/em\u003e spp. (n\u0026thinsp;=\u0026thinsp;137; 22.2%). Other species such as \u003cem\u003eArvicanthis niloticus\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;53; 8.6%), \u003cem\u003eMastomys erythroleucus\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;35; 5.7%), \u003cem\u003ePraomys daltoni\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;24; 3.7%) and \u003cem\u003eMastomys natalensis\u003c/em\u003e (n\u0026thinsp;=\u0026thinsp;11; 1,8%) occurred at lower frequencies, while additional taxa (\u003cem\u003eSteatomys\u003c/em\u003e sp., \u003cem\u003eNannomys\u003c/em\u003e, \u003cem\u003eGerbilliscus gambianus\u003c/em\u003e) were only sporadically detected.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eR. rattus\u003c/em\u003e was widely distributed, with higher numbers recorded in Goumbayel, Diank\u0026eacute; Makha, Gouloumbou and Dide Gassama, while \u003cem\u003eM. musculus\u003c/em\u003e showed a similarly broad distribution, particularly in Mbirkilane, Sinthiou Mal\u0026egrave;me, Goudiri, Niah\u0026egrave;ne (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003e). By contrast, \u003cem\u003eMastomys natalensis\u003c/em\u003e was rare and detected only in the southeastern sites: K\u0026eacute;dougou, Mako and Segou. Overall, \u003cem\u003eR. rattus\u003c/em\u003e and \u003cem\u003eM. musculus\u003c/em\u003e were dominant and widespread, especially in roadside villages, whereas recognized LASV reservoir species were found only occasionally and in low numbers.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSex ratios varied across species captured (figure \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e). \u003cem\u003eRattus rattus\u003c/em\u003e (57.5% females) and \u003cem\u003eMus musculus\u003c/em\u003e (59.8% females) showed significant female bias, while \u003cem\u003eCrocidura\u003c/em\u003e sp., \u003cem\u003eArvicanthis niloticus\u003c/em\u003e, \u003cem\u003eM. erythroleucus\u003c/em\u003e, and \u003cem\u003eM. natalensis\u003c/em\u003e displayed more balanced distributions. \u003cem\u003ePraomys daltoni\u003c/em\u003e also showed a female predominance (68.2%), whereas rare taxa (\u003cem\u003eGerbilliscus gambianus\u003c/em\u003e, \u003cem\u003eNannomys\u003c/em\u003e, \u003cem\u003eSteatomys\u003c/em\u003e sp.) were represented by very few individuals, limiting interpretation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eOf the 618 sera tested, 11 (1.8%; 95% CI: 0.9\u0026ndash;3.2%) were positive for LASV-specific IgG (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). All seropositive samples originated from commensal species, namely \u003cem\u003eRattus rattus\u003c/em\u003e (9/180; 5%) and \u003cem\u003eMus musculus\u003c/em\u003e (2/174; 1.1%). No IgM antibodies were detected, indicating an absence of acute infections among the archived specimens.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cb\u003eSummary statistics of LASV IgG ELISA results in rodents from Senegal (2012\u0026ndash;2013).\u003c/b\u003e Descriptive statistics of LASV IgG ELISA index values (IVsample​ value) according to serological status. Among 618 sera tested, 11 (1.8%; 95% CI: 0.9\u0026ndash;3.2%) were positive for LASV-specific IgG, all from commensal species, \u003cem\u003eRattus rattus\u003c/em\u003e (5%) and \u003cem\u003eMus musculus\u003c/em\u003e (1.1%). No IgM antibodies were detected, indicating no evidence of acute infection in the archived specimens.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSerological status\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean (IVsample)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eStandard deviation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eMedian\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMin. (IVsample)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eMax. (IVsample)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEquivocal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.944\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.045\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.942\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.901\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.991\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNegative\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e604\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.285\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.114\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.254\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.112\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.891\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePositive\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.934\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.949\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.470\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.124\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e3.816\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eSeropositive samples were geographically clustered in five villages located along major transport and border corridors (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The corresponding IVsample values for positive specimens ranged from approximately 1.12 to 3.82 (mean\u0026thinsp;=\u0026thinsp;1.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, figure \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Three additional sera (0.5%) yielded equivocal results (mean IVsample value\u0026thinsp;=\u0026thinsp;0.944\u0026thinsp;\u0026plusmn;\u0026thinsp;0.045), indicating sporadic intermediate antibody reactivity. These were detected in \u003cem\u003eArvicanthis niloticus\u003c/em\u003e from Ida Seco and in \u003cem\u003eMus musculus\u003c/em\u003e from Gandiaye and Kidira.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eStatistical comparisons between exposed species were performed using the Mann\u0026ndash;Whitney U test to evaluate differences in LASV-specific IgG responses (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Although \u003cem\u003eRattus rattus\u003c/em\u003e exhibited a trend toward broader and stronger immune responses compared to \u003cem\u003eMus musculus\u003c/em\u003e (mean IVsample: 2.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99 vs. 1.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15), this difference did not reach statistical significance (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). These findings suggest that the two species may experience comparable levels of exposure or susceptibility, although interpretation is limited by the small sample size, particularly for \u003cem\u003eM. musculus\u003c/em\u003e. Spatial analysis further indicated that several individuals from Did\u0026eacute; Gassama displayed particularly high immune responses (mean IVsample: 2.66\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00) relative to individuals from other localities. However, these geographic differences were also not statistically significant (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e4\u003c/span\u003eB).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e(B)\u003c/b\u003e Spatial variation in IgG responses across LASV-seropositive localities. Individuals from Did\u0026eacute; Gassama exhibited the highest mean IgG values (2.66\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00), but no significant differences were observed among sites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The dashed red line represents the positive threshold (IVsample_{sample}sample​ = 1.1).\u003c/p\u003e\u003cp\u003eAt the site level, mean Shannon diversity was lower in LASV-positive localities (H\u0026prime; \u0026asymp; 0.35) than in LASV-negative localities (H\u0026prime; \u0026asymp; 0.70), suggesting a tendency toward reduced species diversity where LASV exposure was detected. This pattern was also apparent in the diversity\u0026ndash;positivity scatterplot, where a weak negative correlation was observed (r = \u0026minus;\u0026thinsp;0.21, R\u0026sup2; = 0.044). However, neither the Mann\u0026ndash;Whitney U test (p\u0026thinsp;=\u0026thinsp;0.14) nor the correlation analysis (p\u0026thinsp;=\u0026thinsp;0.093) reached statistical significance, indicating that the association between species diversity and LASV seropositivity remains suggestive but inconclusive (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur results indicate that, in addition to \u003cem\u003eMastomys natalensis\u003c/em\u003e, commensal rodents such as the black rat \u003cem\u003eR. rattus\u003c/em\u003e and the house mouse \u003cem\u003eM. musculus\u003c/em\u003e can play a role in LASV exposure. Field surveys in Nigeria found \u003cem\u003eR. rattus\u003c/em\u003e and \u003cem\u003eM. musculus\u003c/em\u003e constituted large fractions of captured rodents, and both species tested positive for LASV by PCR. For example, Agbonlahor \u003cem\u003eet al.\u003c/em\u003e reported that \u003cem\u003eM. musculus\u003c/em\u003e (39.4%) and \u003cem\u003eR. rattus\u003c/em\u003e (36.1%) were the dominant species in rodent collections, and PCR-detected LASV in all three of these (and \u003cem\u003eM. natalensis\u003c/em\u003e) in LASV-endemic states (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Similarly, Happi \u003cem\u003eet al.\u003c/em\u003e found all captured rodent genera (including \u003cem\u003eRattus\u003c/em\u003e and \u003cem\u003eMus\u003c/em\u003e) had LASV positivity, with \u003cem\u003eRattus\u003c/em\u003e spp. having the highest infection rate (77.3% in Ondo State, Nigeria) compared to 41.6% for \u003cem\u003eMastomys\u003c/em\u003e spp. in Ebonyi State (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Our detection of LASV IgG in \u003cem\u003eRattus\u003c/em\u003e and \u003cem\u003eMus\u003c/em\u003e from Senegal aligns with these regional findings, suggesting that multiple commensal species may contribute to arenavirus exposure patterns in domestic settings (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOur data confirm that non-\u003cem\u003eMastomys\u003c/em\u003e synanthropes in West Africa can harbor LASV, underscoring their potential as secondary reservoirs or as part of complex transmission webs.\u003c/p\u003e\u003cp\u003eRecent ecological studies in Senegal further confirm that \u003cem\u003eR. rattus\u003c/em\u003e and \u003cem\u003eM. musculus\u003c/em\u003e dominate commensal rodent communities in many villages, often displacing native \u003cem\u003eM. natalensis\u003c/em\u003e (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Such displacement can alter community structure and potentially reshape LASV transmission dynamics. In our study, LASV-positive sites showed lower mean Shannon diversity than negative sites, a trend consistent with simplified communities dominated by invasive commensals potentially altering LASV exposure dynamics, although this association did not reach statistical significance.\u003c/p\u003e\u003cp\u003eThe role of invasive commensals is nuanced. On one hand, increased rodent biodiversity, particularly replacement of the primary reservoir, could dilute LASV transmission. Historical data from Guinea show that coastal regions dominated by introduced \u003cem\u003eR. rattus\u003c/em\u003e and \u003cem\u003eM. musculus\u003c/em\u003e had low human Lassa seroprevalence, whereas inland areas with many \u003cem\u003eM. natalensis\u003c/em\u003e had high LASV antibody rates. Fichet-Calvet \u003cem\u003eet al.\u003c/em\u003e found a negative relationship between non-native rodents and Lassa risk: prefectures where \u003cem\u003eM. musculus\u003c/em\u003e predominated (and \u003cem\u003eM. natalensis\u003c/em\u003e was scarce) unexpectedly had low Lassa antibody prevalence in people (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). More recently, Eskew \u003cem\u003eet al.\u003c/em\u003e showed that invasion by \u003cem\u003eR. rattus\u003c/em\u003e in Sierra Leone/Guinea strongly depressed \u003cem\u003eM. natalensis\u003c/em\u003e house density and correlated with reduced LASV spillover risk (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). In other words, invasive \u003cem\u003eR. rattus\u003c/em\u003e appear to have an indirect \u0026ldquo;dilution\u0026rdquo; effect by outcompeting the primary reservoir in domestic settings.\u003c/p\u003e\u003cp\u003eOn the other hand, invasive commensals themselves may become LASV sources. The Nigerian surveys above demonstrate that \u003cem\u003eR. rattus\u003c/em\u003e and \u003cem\u003eM. musculus\u003c/em\u003e can carry LASV at rates comparable to or exceeding \u003cem\u003eMastomys\u003c/em\u003e. In Ondo State, \u003cem\u003eRattus\u003c/em\u003e spp. had 77% LASV positivity versus 41% in \u003cem\u003eMastomys\u003c/em\u003e (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). This implies that under certain ecological or anthropogenic contexts such as high rodent density in trade hubs, non-native species could act as amplifying hosts or bridge species between wildlife and humans.\u003c/p\u003e\u003cp\u003eLikewise, experimental and genetic studies suggest that newly invasive \u003cem\u003eM. musculus\u003c/em\u003e encounters high parasite pressure in Senegal: immune gene expression was elevated in house mice at recent invasion fronts, hinting at increased infection risk when \u003cem\u003eM. musculus\u003c/em\u003e colonizes new areas (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eTogether, these findings reveal a dual ecological reality: invasion may suppress traditional reservoirs yet simultaneously open new niches for viral maintenance. The net epidemiological outcome depends on local community composition, land-use patterns, and human\u0026ndash;rodent contact frequency.\u003c/p\u003e\u003cp\u003eEnvironmental and seasonal dynamics further modulate LASV risk across West Africa. Climatic and ecological changes are predicted to alter Mastomys demography and thus human risk. Modeling of Mastomys in West Africa suggests that shifts in the timing or synchrony of the rodent breeding season (driven by climate or land-use change) would change the peak of LASV prevalence in rodents, and hence the timing of human risk (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Empirical incidence data in Nigeria support a strong seasonality: spillover to humans surges in the dry season (December\u0026ndash;March), coinciding with peak rodent population fluctuations (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). These ecological insights reinforce that Lassa virus circulation is dynamic, responsive to both natural and anthropogenic pressures.\u003c/p\u003e\u003cp\u003eOur study has limitations that must be acknowledged. Because our rodent data were retrospective and based on serology, we cannot confirm active LASV infection or identify viral lineages. Future efforts combining molecular detection, viral sequencing, and ecological metadata are needed to clarify the genetic diversity and temporal dynamics of LASV in Senegal. Additionally, the cross-sectional design cannot capture seasonal fluctuations or direct transmission chains. Nevertheless, strengths include use of a high-specificity ELISA validated for LASV IgG detection, a relatively large geographic coverage, and rigorous species identification. These provide a valuable baseline for integrating rodent surveillance into broader One Health monitoring frameworks.\u003c/p\u003e\u003cp\u003eFrom a public-health and One Health perspective, our findings have several implications. First, the detection of LASV antibodies in Senegalese rodents extends the known ecological range of the virus and underscores the need to maintain vigilance in regions previously considered non-endemic. Integrating animal surveillance within existing national systems would enable early detection of silent circulation. Second, collaboration with regional and international bodies such as the West African Health Organization (WAHO), the World Health Organization (WHO), Africa CDC, and the World Organisation for Animal Health (WOAH) could help harmonize cross-border animal and human surveillance systems. Coordinated serological and genomic monitoring of rodents and other reservoirs would strengthen One Health preparedness for emerging zoonoses in West Africa. Third, linking environmental monitoring, community education, and rodent-control interventions to socioeconomic indicators could mitigate poverty-related exposure risks.\u003c/p\u003e\u003cp\u003eUltimately, our findings highlight important One Health implications. They suggest that LASV prevention requires integrated surveillance across wildlife, domestic animals and human health sectors. Past reviews emphasize that intensifying interdisciplinary (One Health) efforts is essential to improve LASV surveillance and control in West Africa (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). In practical terms, this means combining rodent ecology monitoring (including both native and invasive species) with human case surveillance. For public health, understanding where non-\u003cem\u003eMastomys\u003c/em\u003e rodents flourish, and how seasonal or environmental changes affect them, can help target interventions (e.g. seasonal sanitation or rodent control) to reduce spillover. Controlling Lassa fever in Senegal and the region will require a coordinated strategy that accounts for shifts in rodent community composition, invasion dynamics, and seasonal ecology. Such a One Health approach, linking animal reservoir studies with clinical surveillance, will be critical to anticipate and mitigate LASV emergence in human populations.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe gratefully acknowledge Laurent Granjon, Christophe Amidi Diagne, and the CBGP teams of the Institut de Recherche pour le Développement (IRD) in Montpellier (France) and Dakar (Senegal) for their exceptional contributions to the rodent trapping efforts. We also thank Pascal Handschumacher, principal investigator of the CHANCIRA project, for his valuable support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFieldwork and samples archiving were supported by the Agence Nationale de la Recherche (ANR) through the CHANCIRA project (ANR-11-CEPL-010). Laboratory investigations were funded by internal resources of the Institut Pasteur de Dakar. The authors declare that no author received any payment or financial support from pharmaceutical companies or external agencies for the preparation of this manuscript. The corresponding author affirms that all authors had full access to the data and accept responsibility for the decision to submit the manuscript for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;S.S. and M.K. performed the laboratory experiments, curated the data, and contributed to the formal analysis. S.Sa. supervised and validated the experimental work. N.D., G.F., O.F., and M.Di. provided resources, while M.Di., N.D., and M.M.D. secured funding. The study was conceptualized by A.G. and M.M.D. M.M.D. also performed the formal analysis, prepared the figures, and managed project administration. S.S., A.G., and M.M.D. wrote the main manuscript text. All authors reviewed and approved the final version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEskew, E. A. et al. Reservoir displacement by an invasive rodent reduces Lassa virus zoonotic spillover risk. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cb\u003e15\u003c/b\u003e (1), 3589 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOgundele, G. O., Jolayemi, K. O. \u0026amp; Bello, S. Lassa fever in West Africa: a systematic review and meta-analysis of attack rates, case fatality rates and risk factors. \u003cem\u003eBMC Public. Health\u003c/em\u003e. \u003cb\u003e25\u003c/b\u003e (1), 2948 (2025).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDemby, A. H. et al. Lassa Fever in Guinea: II. Distribution and Prevalence of Lassa Virus Infection in Small Mammals. \u003cem\u003eVector-Borne Zoonotic Dis.\u003c/em\u003e \u003cb\u003e1\u003c/b\u003e (4), 283\u0026ndash;297 (2001).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFichet-Calvet, E. et al. Fluctuation of Abundance and Lassa Virus Prevalence in Mastomys natalensis in Guinea, West Africa. \u003cem\u003eVector-Borne Zoonotic Dis.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (2), 119\u0026ndash;128 (2007 June).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFichet-Calvet, E., Becker-Ziaja, B., Koivogui, L. \u0026amp; G\u0026uuml;nther, S. Lassa Serology in Natural Populations of Rodents and Horizontal Transmission. Vector Borne Zoonotic Dis. Sept 1;14(9):665\u0026ndash;74. (2014).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSafronetz, D. et al. Geographic Distribution and Genetic Characterization of Lassa Virus in Sub-Saharan Mali. \u003cem\u003ePLoS Negl. Trop. Dis.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (12), e2582 (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOlayemi, A. et al. Widespread arenavirus occurrence and seroprevalence in small mammals, Nigeria. \u003cem\u003eParasit. Vectors 2018 July\u003c/em\u003e \u003cb\u003e13\u003c/b\u003e;11(1):416 .\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSaluzzo, J. F., Adam, F., McCormick, J. B. \u0026amp; Digoutte, J. P. Lassa fever virus in Senegal. \u003cem\u003eJ. Infect. Dis.\u003c/em\u003e \u003cb\u003e157\u003c/b\u003e (3), 605 (1988).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDalecky, A. et al. Range expansion of the invasive house mouse Mus musculus domesticus in Senegal, West Africa: a synthesis of trapping data over three decades, 1983\u0026ndash;2014. \u003cem\u003eMammal Rev.\u003c/em\u003e \u003cb\u003e45\u003c/b\u003e (3), 176\u0026ndash;190 (2015).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSoubrier, H. et al. Detection of Lassa Virus-Reactive IgG Antibodies in Wild Rodents: Validation of a Capture Enzyme-Linked Immunological Assay. \u003cem\u003eViruses\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e (5), 993 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAgbonlahor, D. E. et al. Prevalence of Lassa virus among rodents trapped in three South-South States of Nigeria. \u003cem\u003eJ. Vector Borne Dis.\u003c/em\u003e \u003cb\u003e54\u003c/b\u003e (2), 146\u0026ndash;150 (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHappi, A. N. et al. Increased Prevalence of Lassa Fever Virus-Positive Rodents and Diversity of Infected Species Found during Human Lassa Fever Epidemics in Nigeria. \u003cem\u003eMicrobiol. Spectr.\u003c/em\u003e \u003cb\u003e10\u003c/b\u003e (4), e00366\u0026ndash;e00322 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFichet-Calvet, E. \u0026amp; Rogers, D. J. Risk maps of Lassa fever in West Africa. \u003cem\u003ePLoS Negl. Trop. Dis.\u003c/em\u003e \u003cb\u003e3\u003c/b\u003e (3), e388 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHastie, K. M. et al. The Arenaviridae Family: Knowledge Gaps, Animal Models, Countermeasures, and Prototype Pathogens. \u003cem\u003eJ. Infect. Dis.\u003c/em\u003e \u003cb\u003e228\u003c/b\u003e (Suppl 6), S359\u0026ndash;S375 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGranjon, L. et al. Sharing space between native and invasive small mammals: Study of commensal communities in Senegal. \u003cem\u003eEcol. Evol.\u003c/em\u003e \u003cb\u003e20\u003c/b\u003e (9), e10539 (2023 Sept).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFichet-Calvet, E. et al. Spatial distribution of commensal rodents in regions with high and low Lassa fever prevalence in Guinea. \u003cem\u003eBelg. J. Zool.\u003c/em\u003e \u003cb\u003e135\u003c/b\u003e, 63\u0026ndash;67 (2005).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCharbonnel, N. et al. Differential immune gene expression associated with contemporary range expansion in two invasive rodents in Senegal. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cb\u003e10\u003c/b\u003e (1), 18257 (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJohn, R. S., Fatoyinbo, H. O. \u0026amp; Hayman, D. T. S. Modelling Lassa virus dynamics in West African Mastomys natalensis and the impact of human activities. J R Soc Interface. July 24;21(216):20240106. (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMcKendrick, J. Q., Tennant, W. S. D. \u0026amp; Tildesley, M. J. Modelling seasonality of Lassa fever incidences and vector dynamics in Nigeria. \u003cem\u003ePLoS Negl. Trop. Dis.\u003c/em\u003e \u003cb\u003e17\u003c/b\u003e (11), e0011543 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArruda, L. B. et al. The niche of One Health approaches in Lassa fever surveillance and control. \u003cem\u003eAnn. Clin. Microbiol. Antimicrob.\u003c/em\u003e \u003cb\u003e20\u003c/b\u003e (1), 29 (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"Lassa virus, Rodent reservoirs, Invasive species, One Health surveillance, Zoonotic emergence, Senegal","lastPublishedDoi":"10.21203/rs.3.rs-7946956/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7946956/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eLassa fever, a neglected zoonotic hemorrhagic disease caused by Lassa virus (LASV) and endemic in West Africa, remains a major public health concern linked to rodent exposure. Senegal lies at the western fringe of LASV area, but only one 1988 serosurvey reported low antibody prevalence. Given recent ecological shifts, including expansion of invasive \u003cem\u003eRattus rattus\u003c/em\u003e and \u003cem\u003eMus musculus\u003c/em\u003e, we reassessed LASV exposure in domestic and peri-domestic rodents.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eWe retrospectively analyzed 618 archived rodent sera collected in 2012\u0026ndash;2013 from domestic and peri-domestic environments in central and eastern Senegal. Samples were screened by ELISA for LASV IgG and IgM using validated Panadea assays. Spatial mapping and ecological analysis identified seropositivity clusters and potential environmental correlates.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eEleven rodents (1.8%; 95% CI: 0.9\u0026ndash;3.2%) were positive for LASV\u0026ndash;specific IgG, with no IgM detected, indicating absence of acute infection. Seropositive animals occurred in five villages clustered along major transport corridors and belonged exclusively to commensal species, \u003cem\u003eRattus rattus\u003c/em\u003e (5%) and \u003cem\u003eMus musculus\u003c/em\u003e (1.1%), within low-diversity rodent communities dominated by invasive taxa.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eThis study provides the first update in over three decades on LASV exposure in Senegalese rodents. IgG detection confined to invasive commensal species suggests shifting reservoir dynamics, while reduced diversity at positive sites may indicate a dilution effect. Spatial clustering of seropositive rodents along major transport routes points to low-level but persistent circulation in settings favoring human\u0026ndash;rodent contact. These findings highlight the need to integrate rodent surveillance into One Health frameworks to strengthen early warning and regional preparedness.\u003c/p\u003e","manuscriptTitle":"Serological Evidence of Lassa Virus in Commensal Rodents from Senegal.","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-05 05:03:19","doi":"10.21203/rs.3.rs-7946956/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":"c82cb78e-f667-4b88-a5f4-362fba0013bb","owner":[],"postedDate":"December 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":59131527,"name":"Health sciences/Diseases"},{"id":59131528,"name":"Biological sciences/Ecology"},{"id":59131529,"name":"Earth and environmental sciences/Ecology"},{"id":59131530,"name":"Biological sciences/Microbiology"},{"id":59131531,"name":"Biological sciences/Zoology"}],"tags":[],"updatedAt":"2025-12-05T05:03:19+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-05 05:03:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7946956","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7946956","identity":"rs-7946956","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}