Washington Owners Urged to Vaccinate Horses Against WNV

Washington Owners Urged to Vaccinate Horses Against WNV

Photo: Erica Larson, News Editor

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 (WNV).

“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,” said state veterinarian Brian Joseph, DVM.

In 2016 Washington had 27 confirmed equine WNV cases, seven of which died or were euthanized. In 2015, there were 36 confirmed cases statewide.

The WNV vaccines have 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.

West Nile is transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations; hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

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 could accumulate, like old tires or bird baths. It also helps to refresh the water in troughs at least weekly.

Washington veterinarians who diagnose potential West Nile virus cases should contact the State Veterinarian’s Office at 360/902-1878.

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