West Nile virus detected in Yakima County horse

OLYMPIA, WA – Washington State Department of Agriculture (WSDA) has reported the first case of West Nile virus (WNV) in a Yakima County horse this year. On September 11, the Washington Animal Disease Diagnostic Laboratory (WADDL) confirmed a 1-year-old thoroughbred horse tested positive for the virus after presenting with neurologic signs. This comes after the Washington State Department of Health (DOH) has reported positive mosquito pools in Benton, Grant and Yakima Counties, in coordination with mosquito control district and local health partners.

What this means for animal owners

West Nile virus (WNV) is spread by mosquitoes and can affect horses, birds and people. The disease is not spread by horse-to-horse or horse-to-human contact. While this is Yakima County’s first confirmed case in an animal this year, WNV appears annually in Washington during mosquito season, mostly during the summer and early fall months when mosquito activity is highest. Horses are particularly vulnerable because they have no natural immunity and annual vaccination can improve outcomes. The fatality rate for horses exhibiting clinical signs can be 33% and those that recover can exhibit residual effects such as gait abnormalities for up to 6 months. The risk level for other horse owners in Yakima and surrounding areas is currently moderate, and all animal owners should take preventive steps.

“Even as temperatures begin to cool in the evenings, mosquitoes that carry WNV and other mosquito-borne diseases remain active until a hard freeze occurs. It is important for all animal owners to continue taking precautions to protect animals and themselves from mosquito exposure,” said Dr. Amber Itle, VMD, MS, State Veterinarian, Washington State Department of Agriculture.

WSDA recommends that animal owners:

• Contact a veterinarian about vaccinating horses against WNV and other mosquito-borne diseases.
• Place livestock in barns or sheltered areas with fans during peak mosquito activity (dusk to dawn).
• Eliminate standing water where mosquitoes can breed. If emptying is not possible, cover water sources or change water at least twice per week.
• Use insect repellents approved for the species.

Similarly, DOH recommends that people take precautions to avoid mosquito bites to prevent disease. Use an EPA-registered insect repellent and wear long sleeves when spending time in areas with mosquitoes, stay indoors at dawn and dusk if possible, and use screens on windows and doors.

Signs and symptoms

Animal owners should contact a veterinarian if a horse shows signs of illness, such as mild fever, stumbling, weakness or difficulty standing, which can progress rapidly.

Risk to humans

While horses are highly susceptible to West Nile virus, people can also be infected. Individuals in areas with WNV activity should continue taking precautions. For more information on protecting yourself, visit the Washington State Department of Health.

For Yakima County and surrounding communities

This detection signals that West Nile virus is present in local mosquito populations. While WNV is expected each year during warmer months, this case highlights the importance of mosquito control and vaccination to protect animals and the community.
For more information on West Nile virus and protecting animals, visit WSDA's website. A detailed map of mosquito surveillance is available from VectorSurv.

Up-to-date West Nile virus activity data can also be found on the Washington State Department of Health website.

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