The Washington State Department of Agriculture (WSDA) is reporting that an unvaccinated horse in Omak is the second case of equine West Nile virus confirmed in the state this summer. The 17-year-old palomino gelding was not vaccinated for the virus and has not traveled out of state. The horse is responding to treatment at this time.

The Washington Animal Disease Diagnostic Laboratory in Pullman reported the positive test results to the State Veterinarian’s Office on Friday. The state’s first case of equine West Nile virus this year was reported Aug. 19, involving a Franklin County horse that was not vaccinated. That horse was euthanized.

Washington had two confirmed cases of horses with West Nile virus last year; one in Franklin County and another in Yakima County. The Omak horse is the first reported case of West Nile virus in Okanogan County in recent years, according to Acting State Veterinarian Paul Kohrs. In 2009, British Columbia reported a case across the border north of Okanogan County.

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 from horses to people or other animals. The virus is fatal to horses in about a third of the cases in which clinical signs are apparent, although most horses do not become ill and show no symptoms. Horses that do become ill can appear to be displaying loss of coordination, loss of appetite, confusion, fever, stiffness, and muscle weakness, particularly in the hindquarters.

Spring is the best time to vaccinate horses against West Nile virus or obtain booster shots. Besides vaccination, horse owners can take steps 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.