Ask the Infectious Disease Expert

Can Exercise Help Detect Silent Shedders of Common Respiratory Pathogens?

By Cara Wright, DVM, MS, IVCA

As equine veterinarians, we’re all too familiar with the turmoil respiratory disease outbreaks can cause for our horses and equestrian events. Current preventive measures focus on identifying and isolating sick horses, but little attention is given to testing healthy horses at events. Previous studies have highlighted the importance of identifying silently infected horses, especially regarding equine herpesvirus-1 (EHV-1) and Streptococcus equi spp equi (S. equi), as a potential source of infection. Finding these horses is a challenge. Concurrently, prior work has shown that less invasive sample collection has high agreement with nasal swabs for both EHV-1 and 2.

Our new study1, “Investigation of the role of exercise in the detection of selected respiratory pathogens from nose wipes collected from healthy horses,” examined this very issue by testing healthy horses at racetracks and horse show training barns. The study aimed to determine if exercise increases the frequency of selected respiratory viruses/bacteria shedding in non-clinical horses using nose wipes.

Samples were collected from 133 horses across three racetracks in California, Oklahoma and Maryland, as well as three horse show training barns in California during April and May 2024. The study population included diverse breeds and ages, with Thoroughbreds and Quarter Horses engaged in racing activities, and Warmbloods, ponies and Lusitanos participating in shows. Each horse had its nose wiped before and after routine exercise with an individually wrapped sterile saline wipe. Nose wipes were assayed for the presence of selected common (EHV-1, EHV-4, S. equi) and commensal (EHV-2, EHV-5, S. zooepidemicus) respiratory DNA microbes using previously validated qPCR assays.

WHAT WE FOUND
The study results showed that exercise increased the detection frequency of EHV-1, EHV-2, EHV-5 and S. zooepidemicus in nose wipes collected from non-clinical horses. Further, the results showed that absolute quantitation (total number) of the selected respiratory viruses/bacteria was lower in post-exercise samples.

The frequency of commensal respiratory organisms was quite high in our study population—between 45.9% and 54.9% in pre-exercise nose wipes. Interestingly, racing horses showed higher detection rates of EHV-2, EHV-5, and S. zooepidemicus compared to show horses. The high detection rate of EHV-1 in clinically normal racing horses was unexpected, revealing just how common silent EHV-1 shedders are among young horses. Like the commensal viruses/bacteria, EHV-1 was detected more frequently in post-exercise samples. The sporadic detection of EHV-4 and S. equi made it difficult to draw meaningful conclusions about exercise’s effect on their detection.

WHAT DOES THIS MEAN FOR PRACTITIONERS?
While the absolute quantity of pathogens appeared to decrease post-exercise, our detection frequency improved. This suggests that timing your sample collection after exercise might help you identify more carriers than sampling at rest.

We also confirmed that nose wipes seem to be an effective, less invasive collection method that improves horse compliance during sampling — a practical consideration for busy practitioners at events or investigating potential outbreaks. Next research steps include directly comparing nose wipes with the reference standard of nasal swabs.

These findings represent an important step toward better respiratory disease management in our equine patients.

1. C.A. Wright, K. Lawton, S. Barnum, B.W. Craig, B.R. Farwell, J. Blea, C. McCook, N. Pusterla. Investigation of the role of exercise in the detection of selected respiratory pathogens from nose wipes collected from healthy horses, Journal of Equine Veterinary Science, Volume 146, 2025, 105377, ISSN 0737-0806, https://doi.org/10.1016/j.jevs.2025.105377.

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