Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles

Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Equine Veterinary Journal This is a preprint and has not been peer reviewed. Data may be preliminary. 11 April 2025 V1 Latest version Share on Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles Authors : Luke McLinden 0000-0001-5858-4721 [email protected] , Jeremy Kemp-Symonds , Janet Daly , A. M. Blanchard , Andrew Waller 0000-0002-7111-9549 , and Sarah Freeman Authors Info & Affiliations https://doi.org/10.22541/au.174436220.04752464/v1 Published Equine Veterinary Journal Version of record Peer review timeline 2650 views 212 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Background : Infection with Streptococcus equi subspecies equi ( S. equi ) is characterised by acute disease with about 10% of infected animals entering a carrier state. Clinically, infection with S. equi cannot readily be distinguished from infection caused by other respiratory pathogens including Streptococcus equi subsp. zooepidemicus ( S. zooepidemicus ), equine influenza virus and equine herpes virus. Screening protocols, with appropriate quarantining facilities, are important to detect carriers of S. equi and avoid strangles outbreaks. Objectives : Evaluate the effectiveness of the screening process implemented at a UK welfare centre to prevent introduction of strangles. Study design : Retrospective cross-sectional study. Methods : Clinical records of 626 equids admitted to a UK welfare centre between 2017 and 2021 and from horses that developed respiratory signs after admission were reviewed. Results : The screening protocol, which included a clinical examination, paired serology samples (iELISA) taken 6 weeks apart, and bilateral guttural pouch endoscopy to identify abnormalities such as chondroids with lavage for quantitative PCR and culture analysis for S. equi (and often S. zooepidemicus ) detected 34 potential carriers of S. equi or S. zooepidemicus . Of these, 24 (3.8%) were PCR-positive for S. equi , 8 were PCR/culture positive for S. zooepidemicus and 2 were PCR/culture negative but had chondroids. Bilateral guttural pouch endoscopy, with PCR analysis of lavage material, was the most cost-effective method of detecting S. equi carriers. There were no cases of strangles within the general herd after screening and admission of new horses. Main limitations : Variation in the level of detail of clinical records. Conclusions : The screening process resulted in the identification of carriers and maintained a strangles-free herd. Further research is required to elucidate the significance of S. zooepidemicus infection in the guttural pouch. Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles Summary Background : Infection with Streptococcus equi subspecies equi ( S. equi ) is characterised by acute disease with about 10% of infected animals entering a carrier state. Clinically, infection with S. equi cannot readily be distinguished from infection caused by other respiratory pathogens including Streptococcus equi subsp. zooepidemicus ( S. zooepidemicus ), equine influenza virus and equine herpes virus. Screening protocols, with appropriate quarantining facilities, are important to detect carriers of S. equi and avoid strangles outbreaks. Objectives : Evaluate the effectiveness of the screening process implemented at a UK welfare centre to prevent introduction of strangles. Study design : Retrospective cross-sectional study. Methods : Clinical records of 626 equids admitted to a UK welfare centre between 2017 and 2021 and from horses that developed respiratory signs after admission were reviewed. Results : The screening protocol, which included a clinical examination, paired serology samples (iELISA) taken 6 weeks apart, and bilateral guttural pouch endoscopy to identify abnormalities such as chondroids with lavage for quantitative PCR and culture analysis for S. equi (and often S. zooepidemicus ) detected 34 potential carriers of S. equi or S. zooepidemicus . Of these, 24 (3.8%) were PCR-positive for S. equi , 8 were PCR/culture positive for S. zooepidemicus and 2 were PCR/culture negative but had chondroids. Bilateral guttural pouch endoscopy, with PCR analysis of lavage material, was the most cost-effective method of detecting S. equi carriers. There were no cases of strangles within the general herd after screening and admission of new horses. Main limitations : Variation in the level of detail of clinical records. Conclusions : The screening process resulted in the identification of carriers and maintained a strangles-free herd. Further research is required to elucidate the significance of S. zooepidemicus infection in the guttural pouch. Introduction Equine strangles, caused by Streptococcus equi subspecies equi ( S. equi ), is a highly infectious disease that has significant implications for the health and welfare of equids across the globe [1; 2]. The continued persistence of equine strangles can be partly attributed to the presence of carrier animals, in which a viable population of S. equi persists and continues to shed, intermittently or continuously, following the apparent resolution of infection [3]. The identification and treatment of persistently infected equids is important in the control of strangles and the prevention of outbreaks; this could be done in the aftermath of an outbreak or as a dedicated screening protocol. There are many challenges associated with detecting carrier animals and there can be confusion around the effectiveness of the options available to caregivers and clinicians. Repeated nasopharyngeal lavage, on three occasions at least two weeks apart, has been shown to predict freedom from persistent S. equi infection [4], but does not reliably identify equids that are persistently infected. Repeated nasopharyngeal lavage is necessary to mitigate against a high proportion of false negative results but repeated testing is costly due to the need for recurrent veterinary action [5]. The dual target iELISA is unable to reliably identify carrier animals [6] and its main use is in screening for exposure to S. equi following an outbreak to direct further testing. Guttural pouch endoscopy and lavage is considered the best method for carrier detection, despite practical and economic implications, as it allows for a visual inspection of the guttural pouch alongside microbial analysis [1]. The aim of this study was to evaluate the effectiveness of a screening protocol at one of the UK’s largest equine welfare centres, which was established after a severe strangles outbreak some 20 years ago that resulted in significant morbidity and mortality. Materials and methods Study design The target population in this retrospective cross-sectional study was equids that were screened on admission/re-admission to a UK rescue centre over a 5-year period (03 January 2017 – 14 December 2021). The screening protocol took place in a dedicated admission unit. The screening protocol included a clinical examination, paired blood samples taken at least 6 weeks apart for serology, endoscopic examination and lavage of both guttural pouches, with lavage fluid from each guttural pouch separately submitted to a diagnostic laboratory for quantitative PCR analysis and culture for S. equi (and S. zooepidemicus ). Blood samples for serological testing by iELISA and guttural pouch lavage samples for microbial analysis were primarily sent to Rainbow Equine Hospital Limited (Spitfire House, Aviator Court, York YO30 4XT). Occasionally, samples were sent to other RCVS-accredited equine hospitals, including Liphook Equine Hospital (Forest Mere, Liphook, Hampshire GU30 7JG) and Rossdales Laboratories (High Street, Newmarket, Suffolk CB8 8JS). Routine biochemistry and haematology samples were typically processed in-house. Inclusion criteria were all equids that were subject to at least one aspect of this screening protocol, for example foals that were tested serologically but were too small to have endoscopy performed were included. For the purpose of retrospective analysis, the criteria for identifying equids with ‘strangles’ were animals that tested positive for S. equi or S. zooepidemicus through PCR or culture, respectively, on guttural pouch lavage, or an animal that had chondroids in their guttural pouch despite a negative test result. These animals were classified as carriers if they did not display any signs of respiratory or systemic disease. These criteria were shaped by the practicalities of the screening protocol as the primary aim was to prevent strangles and strangles-like presentations from entering the herd. For the duration of the screening process (approximately 6 weeks), equids were housed in a dedicated quarantine unit on a rolling basis, alongside an onsite veterinary team. Once equids entered the general herd, all animals were checked at least once daily by a trained member of staff. Data analysis Using the IDEXX Animana system, admitted equids were ranked by date of first admission. Each animal’s clinical records could then be accessed to allow data retrieval. When clinical data on admitted equids could not be retrieved in this way, for example if they had been readmitted or were deceased, clinical records were obtained from a paper copy. A bespoke data capture form was created with numeric identification codes assigned to the admitted equids to provide anonymity and denote chronology. The form was separated into three sections: contextual, screening, and biochemistry and haematology data. Contextual data included information on key dates (admittance, sampling, and clinical examination). Age, breed, body condition score, sex, and neuter status of equids were also recorded in this section, where available. Screening data included results from the tests performed as part of the screening process (serology, endoscopy, and guttural pouch lavage), as well as a description of relevant clinical signs or guttural pouch abnormalities, such as lymphoid hyperplasia or the presence of chondroids. The results from quantitative PCR analysis were designated either ‘positive’ or ‘negative’; cycle threshold (CT) values were not available for many equids that were PCR positive, therefore these values were not captured. The optical density (OD) data from the serological test, a dual target iELISA, were captured and later converted to a ‘positive’ (OD ≥ 0.5), ‘negative’ (OD < 0.3), or ‘equivocal’ (OD ≥ 0.3 < 0.5) result for analysis. Raw data from biochemistry and haematology tests, typically taken during the initial veterinary assessment and at time of endoscopy were captured and later converted to ‘elevated’, ‘normal’, or ‘lowered’, as defined by the laboratory’s reference range for each parameter (Rainbow Equine Hospital, UK). Data were systematically cleaned to allow identification of discrepancies and inputting errors, ensuring validity. Continuous data were sorted into discrete categories where possible and some categorical data, such as breed, were combined to allow for statistical analysis (Table S1). To confirm the strangles-free status of the herd, all cases of respiratory disease between 2019 and 2021 were extracted and reviewed. This was done by using monthly key performance indicator (KPI) data provided by the rescue centre, and by evaluating the daily clinical diary between 2019 and 2021. Statistical methods Descriptive statistical analysis was used to examine data, with range, mean, median and mode being used to examine continuous variables and percentage frequencies calculated for categorical data. Some equids were not subject to all elements of the screening protocol and clinical data were not recorded or retrievable in some cases, therefore the total number of equids included in each analysis (N) is presented. Two-way pivot tables in Microsoft Excel v2211 were used to examine the interactions between demographic/contextual data and screening data. The statistical software package GraphPad Prizm v9.4.1 was used to perform Fisher’s exact, Chi-square and Chi-square for Trend tests to investigate the association between strangles and host risk factors, biochemistry and haematology results, and seropositivity, using a significance of p<0.05. Results The clinical records of 662 equids were extracted for the 5-year study period. After equids that had not been screened either serologically or endoscopically had been removed, the clinical records of 626 equids remained (Table S2). Fewer equids were admitted during 2020 compared to other years (Figure 1). There was no discernible seasonal variation in admission numbers although the highest numbers were recorded in the first quarters of 2019 (53) and 2021 (52). Between 2017 and 2021, 5.4% (34/626) of equids were identified as ‘strangles’ cases through the screening process with 70.6% (24/34) that were PCR-positive for S. equi and 23.5% (8/34) for S. zooepidemicus , and 5.9% (2/34) that were PCR / culture negative for both S. equi and S. zooepidemicus but had chondroids within their guttural pouches (Figure 1). All 24 guttural pouch lavage samples that were positive for S. equi were positive only by PCR and not by culture, whereas of the S. zooepidemicus positive guttural pouch lavage samples identified, 7 were positive by culture only and 1 by both PCR and culture. The proportion of equids that tested positive for either S. equi or S. zooepidemicus was highest during 2018 (11.3%; 15/133) and 2019 (8.3%; 12/144) and lower during 2017 (2.4%; 3/126) and 2021 (2.8%; 4/141), and none were identified during 2020. Most positive-testing animals (55.9%, 19/34) were admitted during the first quarter of the years analysed, which was also the highest proportion of the number of animals admitted (19/190, 29.4%). There appeared to be a shift in animals testing positive for S. equi or S. zooepidemicus with no S. zooepidemicus positive animals detected in 2017 and no S. equi positive animals detected after the first quarter of 2019. In addition to the animals identified through the screening programme, three horses with S. zooepidemicus infection were detected by positive PCR. One young horse was admitted in July 2019 with nasal discharge, lymphadenopathy, cough, guttural pouch abnormalities, raspy lung sounds and capillary refill time of 3 seconds. Two older horses, one of which had nasal discharge, were admitted on the same day in December 2019 and diagnosed by PCR of nasopharyngeal swab extract. Most equids were identified as carrier animals, 91.2% (31/34), displaying no signs or respiratory or systemic disease (Figure 2). Clinical signs were recorded for a significantly greater (p = 0.02; Fisher’s exact test) proportion of the animals that were S. zooepidemicus positive (5/8, 62.5%) than for animals that were S. equi positive (4/24, 16.7%). Nasal discharge was seen in one animal that was S. equi positive and one that was S. zooepidemicus positive. Respiratory signs (harsh lung sounds) were reported in one of the two PCR/culture-negative animals with chondroids. Guttural pouch abnormalities were seen in two S. equi positive animals (including lymphoid hyperplasia in one) and two S. zooepidemicus positive animals. Chondroids were detected in four of the S. zooepidemicus positive animals and only one of the S. equi positive animals. Four risk factors were investigated for association with strangles: age, sex, breed, and body condition (Table 1). The majority, 60.6% (375/619), of equids were less than 10 years old and only 9.9% (61/619) of equids were over 20 years old on admission. The modal age was 5–9 years old (32.3%, 200/619). The modal breed was cob type (43.6%, 273/626). The modal body condition score was 3.0 (25.2%, 144/571). Sex distribution was 53.0% (331/624) male (of which 70.7% (234/331) were neutered), and 47.0% (293/624) female. Neither age, sex, breed nor body condition score were significantly associated with S. equi carriage, although there was a higher proportion of strangles / S. equi PCR positive cases with lower body condition score than with high scores. None of the 18 biochemistry or haematology parameters for which data were obtained (Tables S3 and S4) were statistically associated with carrier status. The proportion of S. equi PCR positive samples testing positive in the dual-target iELISA (13.6%) was greater than for the rest of the population (7.4%; Table 2), but this was not statistically significant (p > 0.05, Fisher’s exact test). One of the three S. equi positive animals that had a positive first sample in the dual-target iELISA was re-tested and this remained positive. Both S. zooepidemicus positive animals that were positive in the first screening test were re-tested and had a negative result on the second test. All 5 samples from animals identified in the screening that tested positive in the dual-target iELISA were positive against antigen A and only 1 was also positive against antigen C. Overall, of the 45 samples testing positive in the first sample, 28 samples were positive for antigen A but not antigen C, 9 samples were positive for both antigen A and C, and only 8 were positive only for antigen C. There were no suspected or confirmed cases of strangles between 2017 and 2019 (personal communication, veterinary adviser), although respiratory disease was not formally recorded during this time. The retrospective review of clinical records (from monthly KPI records and the daily clinical diary records) between 2019 and 2021 identified 37 cases of respiratory disease within the rescue centre population (Figure S2). None of these were suspected to be strangles cases by the on-site veterinary team. Discussion This study assessed the effectiveness of an admission screening protocol applied to 626 equids between 2017 and 2021. Overall, 34 animals were identified that tested positive for S. equi (24) or S. zooepidemicus (8) through PCR or culture, respectively, on guttural pouch lavage, or had chondroids in their guttural pouch despite a negative PCR test result (2). There were no cases of strangles identified within the main herd following screening suggesting that the isolation and screening protocol was effective. The proportion of animals found to be true cases of strangles, testing PCR positive for S. equi , in this study (3.8%) was remarkably consistent with the findings of a 1-year study of the same population conducted in 2014–2015, which found that 9 of 287 equids (3.1%) were guttural pouch carriers of S. equi [6]. The criteria for identifying equids with ‘strangles’ were animals that tested positive for S. equi or S. zooepidemicus through PCR or culture, respectively, on guttural pouch lavage, or an animal that had chondroids in their guttural pouch despite a negative test result. These criteria were shaped by the practicalities of the screening protocol were purposefully broad to minimise the likelihood that cases of persistent S. equi infection, which may have received a false-negative PCR result, due to the presence of S. zooepidemicus or low levels of shedding from chondroids at the time of sampling were not missed and allowed to enter the herd. It is arguable that S. zooepidemicus -positive and test-negative cases with chondroids should not be classified as strangles since the disease is caused specifically by S. equi . The inclusion of animals that tested positive on guttural pouch lavage for S. zooepidemicus is controversial as there is an ongoing debate regarding the presence of this opportunistic pathogen in the guttural pouch. S. zooepidemicus -positive animals may have previously recovered from strangles, caused by S. equi , prior to repopulation of chondroids or the guttural pouch with S. zooepidemicus . Alternatively, S. zooepidemicus may have acted as a primary pathogen, causing lymph node abscessation that led to the guttural pouch infection [7]. In these circumstances equids could not provide a source of S. equi that could trigger a new outbreak, so would not pose the same risk to the general herd as a true strangles case but were still incorporated in this study’s criteria. Similarly, the inclusion of animals with chondroids but negative microbial test results may have led to over-identification of cases. However, these animals were treated clinically as ‘strangles’ to minimise the potential risk of transmission and to ensure that the wider herd remained protected. In a prospective study, it would be interesting to remove the chondroids in such instances and retest in case the first result was a false negative to better understand whether these animals have the potential to transmit S. equi . Nonetheless, given sufficient resources, the rescue centre preferred to take a comprehensive approach of applying follow-up protocols to these animals to minimise the risk that potentially infectious animals were not identified and treated. This approach, while effective in minimising transmission risk, complicates subsequent interpretation and highlights the need for greater understanding of the clinical impact of these strangles-like presentations. To mitigate issues of over detection and misinterpretation, analysis was also performed with S. equi PCR-positive individuals only. Due to the retrospective nature of the study involving data collected over a 5-year period, there was variation in the detail of data recorded. For example, cycle threshold (CT) values were not recorded alongside the quantitative S. equi PCR results for many of the samples, therefore the decision was made not to extract these data. The absence of CT values limited the assessment of bacterial load; low bacterial load may have explained the lack of detection of S. equi by culture despite most samples being screened by both PCR and culture. It has previously been reported that bacterial culture is insufficient to detect S. equi [8-10]. Despite the long data collection period, it was confirmed that the S. equi protocol used in the main laboratory to which samples were submitted did not change. Eight of the 34 (23.5%) of equids that were classified and handled as potential strangles carriers tested negative for S. equi by qPCR but were positive for S. zooepidemicus by culture, one of which also tested positive by PCR. Equids that tested positive for S. zooepidemicus during screening were significantly more likely (p = 0.02) to display clinical signs associated with bacterial respiratory infection. Samples obtained for the screening programme were not routinely subjected to PCR detection of S. zooepidemicus , hence most S. zooepidemicus infections were detected by culture. A further three horses tested positive for S. zooepidemicus during 2019, with samples obtained apparently outside of the screening process in response to clinical signs suggesting active infections in these animals. Future improvements could include using a duplex qPCR assay that detects both S. equi and S. zooepidemicus for the screening programme. Streptococcus zooepidemicus is a very diverse subspecies with the potential to cause disease across multiple species and body systems [11-16]. In addition, S. zooepidemicus is commonly isolated from the respiratory mucosa of healthy and diseased equids alike [17; 18]; consequently, debate exists over whether it is a commensal, primary pathogen, or an opportunistic pathogen [11; 19; 20]. Strains of S. zooepidemicus have been shown to cause outbreaks across the globe with notable examples in Iceland [21], Sweden [12], the UK [12], and Ethiopia [22]. As implemented, the screening protocol appears to have enabled animals infected with S. zooepidemicus to be intercepted, potentially preventing outbreaks caused by this pathogen also. Questions remain whether it is acting as a primary pathogen or secondary to S. equi , colonising the guttural pouch after the infection has established or after any S. equi present is no longer viable . Further research is required, for example obtaining sequences from chondroids in animals testing positive for S. zooepidemicus but negative for S. equi to characterise the strains that cause upper respiratory disease in equids and determine what circumstances are necessary for colonisation. This study did not identify age, breed, sex of body condition score as risk factors for S. equi carriage. Breed and sex are not typically considered as risk factors in the literature, consistent with findings in this study. Age has been suggested as a risk factor for acute strangles infection [23], but it is not consistently associated [24]. Although not statistically significant, strangles carriage was more prevalent in equids with lower body condition scores in this study. Strangles has been linked to low body condition score in an observational study pre-dating confirmation of carrier animals [23]. A more recent study [24] suggested that equids with a higher body condition score were more likely to be in work and mixing with other equids and thus more likely to be exposed to S. equi , but this was in a developing country setting (Lesotho). The lack of significant association between age, sex, breed or body condition score and S. equi carriage in this study highlights the importance of effective screening protocols for all equids, regardless of host factors. This study also did not find a significant association between S. equi carriage and any biochemistry or haematology result. Haematological parameters such as hyperfibrinogenaemia and neutrophilia have been previously linked to acute strangles infection [5; 25]. Hamlen et al. [26] analysed a group of 23 healthy foals that were experimentally infected with S. equi and Duffee et al. [5] examined the clinical records of equids with confirmed strangles, including acute and persistent cases, alongside control animals. Our study population consisted of a substantial proportion of carrier animals, and the lack of significant changes in markers of inflammation or infection, supports previous work by Pringle et al. [27]. Serological testing has an important role in the management of strangles. Single-target SeM-based iELISAs can aid in the diagnosis of purpura haemorrhagica and metastatic abscessation and can be used to screen for exposure [1; 28]. The dual-target iELISA can also be used to identify recent exposure and it is recommended to do so following an outbreak to identify equids exposed to S. equi [1; 29]. The limitations of the dual-target iELISA for carrier detection have been demonstrated previously [6; 27] and no association between seropositivity and S. equi carriage was also found in this study. It may be that some carriers have such a low bacterial load, or a dormant type of infection, that insufficient bacteria are shed to stimulate an immune response detectable by this assay. Cycle threshold values were not available due to the retrospective nature of the study, and little can be inferred about the bacterial load in the equids with strangles. Antigen A was responsible for detecting more equids. Antigen C is in the genomic region encoding SeM, which has been shown to be subject to genomic decay in some persistent isolates [30]. Antigen A is a segment of the gene SEQ_2190, which encodes a sortase-processed surface protein. This gene may also be lost in some persistent isolates due to genomic decay via a SEQ_2180/SEQ_2190 recombination event [30]. Due to the retrospective nature of the study, isolates were not collected for sequencing to investigate whether the decay of these targets contributed to the occurrence of false-negative results. Despite the limitations for detecting carriers, the dual-target iELISA should continue to be used to identify recently exposed animals. Conclusion Guttural pouch lavage and endoscopy, with sampled material being subject to microbial analysis (PCR) alongside a visual examination of the guttural pouch, was validated as an effective method of detecting persistent strangles infections. Serological testing with the dual-target iELISA was shown to be unable to detect S. equi carrier animals, with no association between carrier and serological status being found. The number of animals testing positive for S. zooepidemicus as part of the screening process suggests that further work is needed to determine whether S. zooepidemicus is acting as a primary pathogen or secondary to S. equi . The screening protocol evaluated in this study enabled a strangles-free herd to be maintained. Through the adoption of screening protocols, as well as other long-term control measures, such as the vaccination of unexposed animals, the prevention and control of strangles is increasingly achievable. Tables Table 1 : Demographic data of equids that were screened for strangles on admission to a UK rescue centre between 2017 and 2021. Age 0–4 175 11 (6.3%) 8 (4.6%) 5–9 200 8 (4.0%) 6 (3.0%) 10–14 97 5 (5.2%) 5 (5.2%) 15–19 86 6 (7.0%) 3 (3.5%) ≥20 61 4 (6.6%) 2 (3.3%) Total 619 34 (5.5%) 24 (3.9%) Sex F 293 18 (6.1%) 13 (4.4%) ME 97 7 (7.2%) 5 (5.2%) MN 234 9 (3.8%) 6 (2.6%) Total 624 34 (6.3%) 24 (3.8%) Body condition score 0.5, 1.0 38 3 (7.9%) 3 (7.9%) 1.5, 2.0 73 6 (8.2%) 3 (4.1%) 0.5–2.0 105 9 (8.6%) 6 (7.1%) 2.5, 3.0 204 13 (6.4%) 9 (4.4%) 3.5–5.0 250 9 (3.6%) 7 (2.9%) 3.5, 4.0 166 6 (3.6%) 5 (3.0%) 4.5, 5.0 90 3 (3.3%) 2 (2.2%) Total 571 33 (5.8%) 22 (3.9%) Breed type 1 Cob type 234 10 (4.3%) 8 (3.4%) Large pony 110 9 (8.2%) 5 (4.5%) Small pony 81 8 (9.9%) 6 (7.4%) Light horse 41 1 (2.4%) 1 (2.4%) Donkey type 19 3 (15.8%) 3 (15.8%) Other 17 0 0 Sports horse type 14 2 (14.3%) 1 (7.1%) Arab type 9 1 (11.1%) 0 Total 525 34 (6.5%) 24 (4.6%) 1 See supplementary table 1 for definition of breed types Table 2 : Serological results for ELISA using S. equi antigens A and C for equids identified during the screening protocol as S. equi PCR positive, S. zooepidemicus culture positive or having chondroids visible on endoscopy compared with equids that were negative according to the screening protocol. Paired serum samples were taken. S. equi PCR positive 3/22 (13.6) 1/19 (5.3%) S. zooepidemicus culture positive 2/8 (25%) 0/7 (0%) Chondroids only detected 0/2 (0%) 0/2 (0%) Screening negative 40/545 (7.3%) 30/494 (6.1%) n = number positive; N = number tested in category, % = percentage positive. Figure legends Figure 1 : Results of guttural pouch lavage samples taken from equids on admission to a UK rescue centre (2017 and 2021) as part of a strangles screening protocol. Figure 2 : Clinical findings of equids with strangles¹ admitted to a UK rescue centre between 2017 and 2021. Supplementary item 1: contextual information on UK rescue centre Supplementary item 2: supplementary data Table S1: Categorisation of breeds/types of equid as described in the clinical records of equids admitted to a UK rescue centre between 2017 and 2021. Table S2: Population demographics and clinical data retrieved from a population of 662 equids admitted to a UK rescue centre Table S3 : Biochemistry results and their association with strangles carriage in a population of rescue equids admitted between 2017 and 2021. Table S4: Haematology results and their association with strangles carriage in a population of rescue equids admitted between 2017 and 2021. Figure S1 : Number of equids presenting with signs of respiratory disease within a UK rescue centre between 2019 and 2021. References [1] Boyle, A.G., Timoney, J.F., Newton, J.R., Hines, M.T., Waller, A.S. and Buchanan, B.R. (2018) Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles-Revised Consensus Statement. J. Vet. Intern. Med. 32 , 633-647. 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Supplementary Material File (figure 1.docx) Download 237.07 KB File (figure 2.docx) Download 182.36 KB Information & Authors Information Version history V1 Version 1 11 April 2025 Peer review timeline Published Equine Veterinary Journal Version of Record 1 Oct 2025 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Equine Veterinary Journal Authors Affiliations Luke McLinden 0000-0001-5858-4721 [email protected] University of Nottingham School of Veterinary Medicine and Science View all articles by this author Jeremy Kemp-Symonds Bransby Horses View all articles by this author Janet Daly University of Nottingham School of Veterinary Medicine and Science View all articles by this author A. M. Blanchard University of Nottingham School of Veterinary Medicine and Science View all articles by this author Andrew Waller 0000-0002-7111-9549 Intervacc AB View all articles by this author Sarah Freeman University of Nottingham School of Veterinary Medicine and Science View all articles by this author Metrics & Citations Metrics Article Usage 2650 views 212 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Luke McLinden, Jeremy Kemp-Symonds, Janet Daly, et al. Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles. Authorea . 11 April 2025. DOI: https://doi.org/10.22541/au.174436220.04752464/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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