Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles.
Abstract: Infection with Streptococcus equi subspecies equi (S. equi) is characterised by acute disease, with about 10% of infected animals remaining persistently infected. Clinically, infection with S. equi cannot readily be distinguished from infection caused by other respiratory pathogens, including Streptococcus equi subspecies zooepidemicus (S. zooepidemicus), equine influenza virus, and equine herpes virus. Screening protocols, with appropriate quarantining facilities, are important to detect horses infected with S. equi and avoid strangles outbreaks. Virulent strains of S. zooepidemicus can also cause strangles-like presentations. Objective: To evaluate the effectiveness of the screening process implemented at a UK welfare centre to prevent the introduction of strangles and strangles-like presentations. Methods: 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. 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 qPCR and culture analysis for S. equi (and often S. zooepidemicus) was implemented during this time. Results: There were 34 screening-positive equids. Of these, 24 (3.8%) were qPCR-positive for S. equi, 8 were qPCR/culture positive for S. zooepidemicus, and 2 were qPCR/culture negative but had chondroids. Bilateral guttural pouch endoscopy, with qPCR analysis of lavage material, was an effective method of screening equids. There were no cases of strangles or strangles-like presentations within the main herds after screening and admission of new horses. Conclusions: Variation in the level of detail of clinical records. Conclusions: The screening process resulted in the identification of screening-positive equids and maintained a strangles-free herd. Further research is required to elucidate the significance of S. zooepidemicus infection in the guttural pouch.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
Publication Date: 2025-10-01 PubMed ID: 41031843PubMed Central: PMC12892369DOI: 10.1111/evj.70080Google Scholar: Lookup
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Summary
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Overview
- This study evaluated the effectiveness of a screening protocol at a UK equine welfare centre designed to prevent the introduction and spread of strangles, an infectious respiratory disease caused by Streptococcus equi subspecies equi (S. equi).
- The protocol used clinical examinations, paired serology testing, and specialized endoscopic techniques to detect infections in horses before admission, successfully maintaining a strangles-free population.
Background
- Strangles is an infectious disease in horses caused mainly by S. equi, characterized by acute respiratory symptoms.
- Approximately 10% of infected horses become persistently infected carriers, posing a risk of disease spread.
- Clinical symptoms of S. equi infection can be difficult to distinguish from other respiratory infections caused by pathogens like Streptococcus equi subspecies zooepidemicus (S. zooepidemicus), equine influenza virus, and equine herpes virus.
- Virulent strains of S. zooepidemicus can cause symptoms similar to strangles, complicating diagnosis.
- Effective screening and quarantine protocols are essential in equine welfare centres to detect and isolate infected horses to prevent outbreaks.
Objectives
- To assess the effectiveness of a screening protocol implemented at a UK rescue/welfare centre in preventing strangles and strangles-like illnesses.
- To evaluate whether the screening method reliably identifies infected horses before they join the main herd.
- To understand the relevance of S. zooepidemicus infections detected during screening.
Methods
- A retrospective cross-sectional study was conducted using clinical records from 626 horses admitted between 2017 and 2021.
- The screening protocol included:
- Initial clinical examinations looking for signs of respiratory disease.
- Paired serology tests using indirect ELISA (iELISA) performed six weeks apart to detect antibodies against S. equi.
- Bilateral guttural pouch endoscopy, a specialized procedure to visually inspect the horse’s guttural pouches for abnormalities such as chondroids (concretions that may harbor bacteria).
- Lavaging (washing out) the guttural pouches and analyzing the fluid using quantitative PCR (qPCR) and bacterial culture to detect S. equi and often S. zooepidemicus.
- The records of horses displaying respiratory signs after admission were also reviewed to monitor for any outbreak.
Results
- Out of 626 horses screened, 34 were positive by the screening protocol:
- 24 horses (3.8%) tested positive for S. equi by qPCR.
- 8 horses tested positive for S. zooepidemicus by qPCR and culture.
- 2 horses had negative qPCR/culture but showed chondroids on endoscopy, indicating possible infection reservoirs.
- Bilateral guttural pouch endoscopy combined with qPCR of lavage samples was demonstrated to be an effective and reliable method for screening for S. equi infection.
- There were no recorded cases of strangles or strangles-like diseases arising within the main horse population after screening and admitting new arrivals, suggesting the protocol successfully prevented disease introduction.
Conclusions
- The implemented screening procedure successfully identified infected horses prior to entry into the main herd, reducing the risk of strangles outbreaks.
- Bilateral guttural pouch endoscopy with lavage and molecular testing is a valuable tool in detecting both overt and carrier states of S. equi infection.
- The presence and significance of S. zooepidemicus infections in guttural pouches warrant further research to clarify their role in disease and strangles-like presentations.
- There was some variability in the quality and detail of clinical records, which may affect the assessment of the screening process.
- Overall, the screening protocol contributed to maintaining a strangles-free status in the horse population under welfare centre care, promoting better animal health and welfare outcomes.
Cite This Article
APA
McLinden LA, Kemp-Symonds JG, Daly JM, Blanchard AM, Waller AS, Freeman SL.
(2025).
Effectiveness of a screening protocol employed at a UK rescue centre to prevent introduction of strangles.
Equine Vet J, 58(2), 466-475.
https://doi.org/10.1111/evj.70080 Publication
Researcher Affiliations
- School of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK.
- Veterinary Division, Bransby Horses, Lincoln, UK.
- School of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK.
- School of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK.
- Intervacc AB, Stockholm, Sweden.
- School of Veterinary Medicine and Science, University of Nottingham, Nottingham, UK.
MeSH Terms
- Animals
- Horses
- Horse Diseases / prevention & control
- Horse Diseases / microbiology
- Horse Diseases / diagnosis
- Horse Diseases / epidemiology
- United Kingdom / epidemiology
- Retrospective Studies
- Streptococcal Infections / veterinary
- Streptococcal Infections / prevention & control
- Streptococcal Infections / diagnosis
- Streptococcal Infections / microbiology
- Streptococcal Infections / epidemiology
- Cross-Sectional Studies
- Streptococcus equi / isolation & purification
- Mass Screening / veterinary
- Female
- Male
- Streptococcus
Grant Funding
- University of Nottingham as part of an MRes Scholarship
Conflict of Interest Statement
The authors declare no conflicts of interest.
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