Frequency of Detection of Respiratory Pathogens in Nasal Secretions From Healthy Sport Horses Attending a Spring Show in California.
Authors: Pusterla Nicola, Sandler-Burtness Emily, Barnum Samantha, Hill Leigh Ann, Mendonsa Eric, Khan Romesa, Portener David, Ridland Hilary, Schumacher Stephen
Journal: Journal of equine veterinary science
Summary
# Respiratory Pathogen Detection in Healthy Sport Horses at Competition Researchers collected nasal secretions and stall swabs from 162 healthy sport horses competing at a California show to establish baseline detection frequencies of common equine respiratory viruses and bacteria using quantitative PCR. The study revealed substantial carriage of commensal pathogens, with EHV-2 and EHV-5 detected in approximately 39% and 36% of nasal samples respectively, whilst *Streptococcus zooepidemicus* was identified in nearly one-fifth of horses—yet clinically important pathogens like equine influenza virus and EHV-1 were absent from nasal secretions. Notably, environmental sampling from stalls showed higher pathogen detection rates overall, particularly *S. zooepidemicus* in nearly two-thirds of stalls and EHV-1 DNA in five clustered stalls from asymptomatic horses, suggesting subclinical shedding and environmental persistence without overt disease spread. For equine professionals, these findings underscore that apparently healthy show horses frequently harbour and shed respiratory pathogens capable of contaminating shared facilities, and that stall hygiene protocols warrant substantial improvement to minimise environmental transmission risk—particularly between competing animals who may have compromised immunity from travel stress and competition pressures. The clustering of EHV-1-positive stalls is particularly noteworthy for veterinarians managing show grounds, as it demonstrates that nucleic acid detection does not necessarily predict clinical disease but does indicate potential for silent pathogen introduction and dissemination.
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Practical Takeaways
- •Healthy-appearing sport horses at shows can shed respiratory pathogens (particularly S. zooepidemicus and herpesviruses) in stall environments, creating disease transmission risk—enhanced stall disinfection protocols are essential between horses
- •EHV-2 and EHV-5 detection in healthy horses does not indicate clinical disease; focus prevention efforts on reducing environmental contamination and managing contact between horses rather than isolating all qPCR-positive animals
- •Subclinical shedders at shows pose a real biosecurity challenge; establish pre-show health screening and isolation protocols, particularly for high-traffic events, to prevent introducing pathogens to home facilities
Key Findings
- •EHV-2 (38.9%) and EHV-5 (36.4%) were most frequently detected in nasal secretions from healthy sport horses, while EIV, EHV-1, EHV-4, and ERAV were absent or rare (0-0.6%)
- •S. zooepidemicus was detected in 19.7% of nasal secretions and 65.8% of stall swabs, indicating significant environmental contamination
- •Five stalls clustered with EHV-1 qPCR-positive results from apparently healthy horses with no clinical disease spread, highlighting subclinical shedding risk
- •Commensal viruses and bacteria were frequently detected in healthy horses, contrasting sharply with the rare detection of well-characterized pathogenic respiratory pathogens