News Notes

EIV Remains Frequently Diagnosed Disease

Equine influenza remains (EIV) a frequently diagnosed respiratory disease, alongside equine herpesvirus type 4 (EHV-4) and Streptococcus equi subspecies equi, according to the latest annual analysis (January–December 2024) from the Equine Biosurveillance Program, an ongoing surveillance study managed by Merck Animal Health and the University of California, Davis, Equine Infectious Disease Research Laboratory.

This trend aligns with the program’s cumulative findings spanning 17 years, which show that EIV consistently ranks among the “big 3” respiratory pathogens affecting horses, according to press materials from Merck Animal Health.

“Every year, we see an uptick in equine influenza cases as horses begin traveling for competitions and training in the spring,” said Duane E. Chappell, DVM, Merck Animal Health. “The virus spreads rapidly through direct horse-to-horse contact, shared equipment and even human handlers who inadvertently carry the virus among horses.”

Analysis of recent EIV cases confirms that horses traveling for events and competitions are at increased risk—58% of horses diagnosed with EIV had a recent history of travel. Most cases occur in show horses, accounting for 42% of reported cases.

“Young horses, those under stress from travel, and those in high-density environments like showgrounds are particularly vulnerable to equine influenza,” Dr. Chappell said. “Vaccination remains the best line of defense against severe illness.”

Given the seasonal rise in cases, veterinarians should urge horse owners to take proactive steps to protect their animals, which includes vaccination, biosecurity, monitoring and quarantine, and practicing good hygiene. MeV