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Equine influenza outbreak in USDA horses in Pullman

PULLMAN, Wash.—Eleven horses housed at Washington State University’s College of Veterinary Medicine have contracted equine influenza. The horses are a USDA research herd used to study tick-borne parasitic disease.

The herd is currently quarantined, and all horses are recovering under veterinary care.

Equine influenza is a common, highly contagious respiratory disease of horses with a near-global distribution. It is caused by an RNA orthomyxovirus, unrelated to coronaviruses. The equine strain of influenza is not known to infect humans or other animal species.

The most common mechanism of spread is via airborne transmission. Infected horses release infective droplets into the air by coughing or snorting which are then inhaled by horses in close proximity.

Horses can also be exposed to the virus by coming into contact with contaminated surfaces such as stalls, wash racks, stocks, water sources, feed, tack, grooming equipment such as wipe rags, and transport vehicles.

Humans can spread the virus from horse to horse by contaminated hands and clothing.

The affected herd at WSU is a closed herd, meaning no animals have entered or exited the premises in the last several months, so it makes determining how the infection was acquired impossible.

The incubation period for the virus is 24 to 72 hours after exposure.

Signs and symptoms of the disease include fever of up to 106.0 F (41.10 C), lethargy, going off feed, muscle pain/weakness resulting in a stiff gait. Horses often develop a harsh to hacking cough which usually precedes the fever. Nasal discharge is initially clear and watery but may vary.

No fevers have been detected in the infected herd at WSU in the last five days.

Death from equine influenza is very rare. Most horses recover within 21 days.

Media contact:

  • Dr. Nina Woodford, director, WSU’s Office of the Campus Veterinarian, 509-335-6246,

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