The Washington State Department of Agriculture (WSDA) is reporting that a two-year-old Andalusian mixed breed mare in Grandview is the first horse in Washington to contract West Nile virus this year. The horse was not vaccinated for the disease and is showing neurologic signs of the illness including stumbling and difficulties eating.


The Washington Animal Disease Diagnostic Laboratory in Pullman, operated by Washington State University, reported the positive test results to WSDA’s State Veterinarian’s Office Friday.

Washington had 36 confirmed cases of horses with West Nile virus last year, leading the nation with nearly 17% of confirmed equine cases. And this year, mosquitoes testing positive for West Nile virus have been trapped in Adams, Benton, Grant, Franklin and Yakima counties.

“It’s never too late to vaccinate your horse for West Nile virus,” said WSDA field veterinarian Dr. Thomas Gilliom. “We’ve had cooler days but when hot summer days return the risks of mosquito bites will increase.”

West Nile virus is spread by mosquitoes that have fed on infected birds. The disease sickens people, horses, birds and other animals, but it does not spread directly from horses to people or other animals.

The disease is fatal to horses in about a third of the cases in which clinical signs are apparent, although most horses do not become ill and show no symptoms. Horses that do become ill can appear to be displaying loss of coordination, loss of appetite, confusion, fever, stiffness, and muscle weakness, particularly in their hindquarters.

Spring is the best time to vaccinate horses against West Nile virus or obtain an annual booster shot. However, horses may still benefit from first-time vaccinations or an annual booster shot.

Besides vaccination, horse owners can take action to limit horse exposure to mosquitoes. For example, reduce or eliminate sources of stagnant or standing water, stable horses during peak mosquito periods (at dawn and dusk), use equine-approved mosquito repellants, place fans inside barns or stalls to maintain air movement, and avoid using incandescent bulbs inside stables at night.