A 2-year-old gelding horse was euthanized near Grandview after being confirmed to have West Nile virus, state agriculture officials said. The horse had not traveled outside of the area and was not vaccinated against the virus.
The virus, which is fatal for about one-third of horses that show symptoms, is spread by mosquitoes that feed on infected birds.
Symptoms for horses include loss of coordination, loss of appetite, confusion, fever, stiffness and muscle weakness, particularly in the hindquarters. But most horses don't become sick or show symptoms.
Although the virus doesn't spread from horses to people, people can become sick after being bitten by an infected mosquito.
No human cases of West Nile have been confirmed in Washington this year.
This is the first confirmed case of West Nile infection in a horse since 2009.
Veterinarians who learn of potential West Nile cases in horses or other animals should call the state Veterinarian's Office at 360-902-1881.