Washington Reports First Equine WNV Case of 2014

Washington Reports First Equine WNV Case of 2014

A viral disease, WNV is transmitted to horses by infected mosquitoes.

Photo: Thinkstock

The Washington State Department of Agriculture has reported that an unvaccinated horse from Mesa, in Franklin County, has contracted West Nile virus (WNV), the first equine case in that state this year. The horse is showing progressive neurologic signs, including hind end paralysis. It was not immediately known if the horse had traveled outside of the state recently.

The state veterinarian's office received the positive test result from the Washington Animal Disease Diagnostic Laboratory in Pullman on Aug. 19. On Monday, the state Department of Health reported a Walla Walla County man as the first Washington resident in 2014 known to have been infected with West Nile virus in that state.

Acting State Veterinarian Paul Kohrs, DVM, noted Washington had two confirmed cases of horses with West Nile virus last year, including a horse in Pasco and one in Outlook in Yakima County. Oregon had six equine cases and Idaho recorded 10 cases last year.

Health Alert: West Nile Virus

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

Kohrs recommends spring as the best time to vaccinate horses against WNV or obtain booster shots. Besides vaccination, horse owners can take steps to limit horse exposure to mosquitoes. For example, reduce or eliminate sources of stagnant or standing water, stable horses during peak mosquito periods (dawn and dusk), use equine-approved mosquito repellants, place fans inside barns or stalls to maintain air movement, and avoid using incandescent bulbs inside stables at night.

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