Monday, October 23, 2017

West Nile virus season waning; Nine horses test positive

Mike Louisell

Washington state had far fewer cases in 2017 of horses infected with West Nile virus than last year.

This year, the West Nile virus was confirmed in nine horses statewide. If the number holds firm, that is far less than the 27 West Nile equine cases recorded in 2016. Most of the horses struck with the disease were not vaccinated. While some of the horses recovered from the illness, others had to be euthanized. 

The nine cases reported this year were confined to four counties. Spokane County had six. Benton, Lincoln and Kittitas counties each had a single horse case confirmed by laboratory testing. Last year, cases of West Nile virus in horses were recorded in 10 counties, all located in Eastern Washington, with Spokane County reporting eight of the illnesses.

The disease can be fatal to horses especially if they show advanced neurological signs. The best way to prevent West Nile virus in horses is by vaccination—a message you’ll be hearing again from WSDA veterinary staff next spring.

The disease is spread by mosquitoes that have fed on infected birds. It does not spread directly from horses to people or other animals. Cold weather, particularly a good freeze or two, will take care of mosquito threats until next spring.

Visit WSDA’s Animal Health webpage for tips on minimizing the risk of West Nile virus for your horses, or go to for more information about West Nile virus activity in our state, including human cases.