West Nile virus (WNV), a potentially fatal disease in horses, has been confirmed in two locations in White Swan southwest of Yakima, the state Department of Agriculture announced on Aug. 17.
A five-year-old gelding was euthanized Aug. 15. In a separately reported case, an 11-year-old mare received care from a veterinarian the evening of Aug. 15.
In both cases, the horses showed signs of central nervous system problems. Neither horse was vaccinated for WNV and neither horse had been out of the area recently.
The positive test results were reported to WSDA Aug. 17 by the Washington Animal Disease Diagnostic Laboratory operated by Washington State University in Pullman.
These are the first confirmed cases this year of horses contracting West Nile virus in Washington.
"Horse owners are underestimating the risk that West Nile virus presents to their horses," said Dr. Leonard Eldridge, state veterinarian. "The best ways to protect horses are vaccination and limiting exposure to mosquitoes."
WNV vaccines are currently available and an annual booster shot should be considered prior to the start of the mosquito season.
Last year, six equine cases of WNV were confirmed in the state, five from Yakima County and one in King County.
West Nile virus is spread by the bite of an infected mosquito and can infect people, horses, many types of birds, and other animals. Humans cannot contract WNV through contact with an infected horse. Infected horses do not spread the disease to other horses or animals. Mosquitoes become carriers when they feed on an infected bird.
Many horses and other animals contracting WNV do not become ill and show no symptoms at all. Horses that contract WNV may show signs such as loss of coordination, loss of appetite, confusion, fever, stiffness and muscle weakness, particularly in the hindquarters. About one-third of horses that become ill die.
Veterinarians and horse owners should report potential cases of West Nile virus in horses by calling the State Veterinarian's Office at (360) 902-1878.