Washington Horses Infected with West Nile Virus

OLYMPIA – The Washington State Department of Agriculture (WSDA) confirmed the presence of West Nile virus in two horses from Grant and Benton counties. The horses, which were not vaccinated or were under-vaccinated for the disease, are both recovering.

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 last week.

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 where clinical signs are apparent. However, most horses do not become ill and show no symptoms. Horses that do become ill can display loss of coordination, loss of appetite, confusion, fever, stiffness, and muscle weakness, particularly in their hindquarters.

Washington State Veterinarian Dr. Amber Itle recommends spring as the best time to vaccinate horses against West Nile virus or obtain an annual booster shot.

“We have seen a decline in Washington state in recent years of this virus in horses, and we believe that is due to horse owners taking action before the season with vaccination. Any horse owner can request this vaccine from their veterinarian,” Dr. Itle said.

However, even if spring has come and gone, horses may still benefit from first-time vaccinations or an annual booster shot at any time of the year. Horse owners not up to date on shots may benefit from a visit with their veterinarian to determine a vaccination protocol that best fits their situation.

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 (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.

Veterinarians who learn of potential West Nile virus cases in horses or other animals should contact the State Veterinarian’s Office at (360) 902-1881.

In 2021, the USDA reported 220 equine cases involving West Nile virus. Numbers for 2022 are not yet posted. Visit the websites of the state Department of Agriculture, Department of Health, or the U.S. Department of Agriculture for more information.

West Nile virus was detected in some horses in Idaho one month ago.

Source: Washington State Department of Agriculture