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West Nile Virus is waking up again

August 20, 2021

Mosquito pools in the Tri-Cities and Walla Walla area have been showing up with positive results for West Nile virus (WNV) and Washington now has four confirmed cases of West Nile Virus in un/under-vaccinated horses. Three of the horses were from Yakima County and a single horse from Kittitas County had a recent travel history in Idaho. One of the diagnosed horses in Yakima was euthanized due to ataxia and recumbency. The vaccination history of the horse is unknown.

The WNV vaccine for horses is very effective at prevention, so this horse was most likely not vaccinated or under-vaccinated. There has also been a person diagnosed with the disease in the Yakima area.

For unvaccinated horses, it will take two injections three weeks apart and a yearly booster. One vaccination usually will help decrease the severity of disease, but full protection needs a booster at the correct time.

Signs of WNV in horses include fever, incoordination, urine dribbling, inability to rise, muscle twitching and staggering.  Diagnosis is based on symptoms and blood testing. There is no treatment for WNV except supportive anti-inflammatories.

Some animals recover in full, while others have neurological deficits for life or will be unable to get up and must be euthanized.  About 33 percent of affected horses will have to be put down.

By Dr. Ben Smith, WSDA field veterinarian


Posted August 20, 2021