Washington state equestrians advised to vaccinate horses for West Nile virus

OLYMPIA — Washington State Veterinarian Dr. Joe Baker is urging owners to vaccinate their horses for West Nile virus, following a year in which Washington had more confirmed equine cases than any other state. Thirty-six horses tested positive for the virus in 2015, according to a press release from the Washington State Department of Agriculture. By comparison, only five cases were reported positive in 2014, all in Eastern Washington.

The state veterinarian’s office is part of the Washington State Department of Agriculture and monitors cases of animal diseases, including West Nile virus. The West Nile virus vaccine has proven to be effective if administered to horses early enough for protection before mosquito season.

“The virus activity varies greatly from year to year, but the risks are real, so I recommend protecting your horses with West Nile virus vaccine,” Baker said. “Most active cases of West Nile virus in Washington tend to develop in the south-central counties when warmer weather starts growing the mosquito population.”

The first confirmed case last year was reported mid-July by Washington State University’s Washington Animal Disease Diagnostic Laboratory in Pullman. There were eight cases in both Yakima and Kittitas counties, seven in Grant County and four in Benton County. In all, 10 counties reported cases.

The virus is potentially fatal to horses and is spread by mosquitoes that have fed on infected birds. While West Nile virus can sicken people, horses, birds and other animals, it does not directly spread from horses to people or other animals.

Horses require two doses of the vaccine initially, and then boosters at least annually.

Most horses exposed to the West Nile virus display no symptoms. Horses that do become ill often display loss of coordination, loss of appetite, confusion, fever, stiffness, and muscle weakness, particularly in their hindquarters. The disease is fatal in about one-third of the cases where clinical signs become apparent.

To reduce the risk, WSDA advises owners to keep horses indoors during the peak mosquito activity times of dawn and dusk, use insect repellant products and fly sheets to reduce exposure, eliminate sources of standing water nearby, and check areas where rain water may accumulate, like old tires or bird baths. It also helps to refresh the water in water troughs weekly.

Veterinarians who diagnose potential West Nile virus cases should contact the State Veterinarian’s Office at (360) 902-1881. Visit WSDA’s West Nile virus webpage or the state Department of Health for more information.