OLYMPIA – The Washington State Department of Agriculture (WSDA) is urging horse owners to vaccinate their animals as soon as possible to protect against West Nile virus.

“Now is the time to vaccinate for this mosquito-borne disease due to our extremely wet winter and Washington’s history of leading the nation with equine cases of the West Nile virus,” State Veterinarian Dr. Brian Joseph said.

Washington had 27 confirmed equine cases last year for the virus. Seven horses died or were euthanized. In 2015, there were 36 confirmed cases statewide.

The West Nile virus vaccine has proven to be effective if administered to horses early enough for protection before mosquito season. The first confirmed case last year was reported in late July by Washington State University’s Washington Animal Disease Diagnostic Laboratory in Pullman. Ten counties reported cases in 2016, involving horses in Benton, Franklin, Grant, Kittitas, Lincoln, Okanogan, Pend Oreille, Spokane, Stevens and Yakima counties. Spokane County lead with eight 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.

“We advise horse owners to consult with their veterinarian to discuss vaccinations for West Nile virus, equine herpes virus and other diseases,” Joseph said.

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 rainwater 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 360-902-1878. Visit WSDA’s West Nile virus webpage or the state Department of Health for more information.