Respiratory Viruses Detected at Shows, Sales

In a survey of horses arriving at several different show and sale facilities, researchers found that as many as 4% of the population were shedding equine herpesvirus-1 (EHV-1) from nasal passages, and as many as 2% were shedding equine herpesvirus-4 (EHV-4), based on a real-time polymerase chain reaction (PCR) tests. Josie Traub-Dargatz, DVM, MS, of Colorado State University's College of Veterinary Medicine and Biomedical Sciences, presented the study data on behalf of Paul Lunn, BVMS, MS, PhD, principal investigator on the study, and graduate student Jennifer Yactor at the 2006 AAEP Convention.

This study showed that horses attending events can shed these viruses from their nares (nasal passages). None of the horses attending these shows or sales demonstrated the neurologic form of EHV-1, and few of the EHV respiratory-positive horses showed signs of disease.

She said the study provided a snapshot of the important viral respiratory pathogens shed by horses at major competitive or sales events. The long-term goals of the study were to test three hypotheses:

  • 1. Young horses attending a major equine competitive event will shed contagious viral pathogens that represent a disease threat to all horses in contact;
  • 2. There is a difference between the rate of shedding at the time of entry to a competitive event and at two to four days after entry. This is caused by stress related to transporting the animal to the event and the mixing of animals; and
  • 3. The shedding of pathogens is associated with risk factors that can be identified in individual horses.

The research was designed as a pilot study to assess the feasibility and likelihood of detecting viral shedding in the tested horses. For this reason, researchers selected horses at greatest risk of infection (such as juvenile horses).

Horses were sampled within 24 hours of arriving at facilities, and when possible, two to four days later. Traub-Dargatz said samples were collected from horses at four equine shows or sales:

  • Barrett's Equine Sales in March 2004 in Pomona, Calif.;
  • the June 2004 National Appaloosa Horse Show and World Championship Appaloosa Youth Show in Oklahoma City, Okla.;
  • the October 2004 Fall Mixed Thoroughbred Sale held by the Ocala Breeder's Sales Company in Ocala, Fla.; and
  • the November 2004 American Quarter Horse Association World Championship Show in Oklahoma City.

The researchers also visited two farms in the Ocala area with suspected respiratory infections.

When possible, researchers completed questionnaires in order to collect information about risk factors associated with viral shedding, such as age, sex, vaccination history, travel history, total horse population at home, and if the home facilities were "open" or "closed" (no horses entering the premises within the last three months).

"This study demonstrated the utility of real-time PCR for the detection of EHV-1 and EHV-4 from nasal secretions from horses," Dargatz said. "Horses at equine events can shed EHV-1 and -4. The majority of horses detected to be shedding were less than two years of age, most had no history of recent illness, and there were positives at multiple events. There were no significant differences from initial and follow-up samples for EHV-1.

The study was funded by Intervet Inc. and grants from the university.


Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse's AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for TheHorse.com .

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