Horse Euthanized With West Nile Virus

A 10-year old mare from north Pasco is the second case of equine West Nile virus reported in Washington for the year. The horse was euthanized.

The horse was not vaccinated for the disease, and had not left the state. West Nile is potentially fatal in infected equines, other mammals and birds. The Washington State University’s Animal Disease Diagnostic Laboratory in Pullman reported the positive test results to the State Veterinarian’s Office earlier this week.

The only other confirmed case of West Nile virus in a Washington horse this year was reported in late September for a horse pastured in Outlook, Yakima County.

“A killing frost will reduce the likelihood of further cases for the year,” said Acting State Veterinarian Paul Kohrs. “Horse owners in areas of the state where this disease will over winter should consider vaccinating for West Nile in 2014 at least a month before the onset of the mosquito season.”

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.

According to the Centers for Disease Control and Prevention, 1,135 human cases have been reported nationwide this year.

West Nile virus is fatal to horses in about a third of the cases where clinical signs are apparent, although most horses do not become ill and show no symptoms at all. Horses that do become ill often display loss of coordination, loss of appetite, confusion, fever, stiffness, and muscle weakness, particularly in their hindquarters.

Washington had 72 West Nile virus cases in horses in 2009, but none in 2010 or 2011. Last year, a horse pastured near Grandview was euthanized after it became ill with the disease.

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.