Time to Consider Vaccinating Horses against WNV

Time to Consider Vaccinating Horses against WNV

Studies have shown that the WNV vaccine has a substantial effect on preventing disease.

Photo: Erica Larson, News Editor

Warmer weather following a rainy spell could trigger an active mosquito season, which is why the Washington State Department of Agriculture (WSDA) is advising horse owners to make sure their horses are vaccinated to protect against West Nile virus (WNV).

Authorities in eastern Washington confirmed two cases of equine WNV last year, however the number has been much higher in previous years. For instance, 72 cases were reported in 2009.

“With mosquito season approaching, now is the time to schedule a visit with your veterinarian for an initial series of vaccine injections if your animals have never been vaccinated before, or for an annual booster injection,” said Paul Kohrs, DVM, acting state veterinarian. “It can take up to four weeks for the immunity offered by the initial series of vaccinations to be fully protective.”

West Nile is a viral disease transmitted to horses by infected mosquitoes. Clinical signs of 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 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%.

Studies have shown that the WNV vaccine has a substantial effect on preventing disease. The American Association of Equine Practitioners recommends vaccinating all foals and horses against WNV. For horses residing in the northern United States veterinarians recommend vaccinating in the spring prior to peak mosquito levels. In the south, where mosquito populations are present year-round, horses might be vaccinated more frequently. In addition to geography, age and exposure play an important role in deciding how often to vaccinate horses, so consult your veterinarian before deciding how many times to vaccinate your animals.

The WSDA is advising owners to keep horses indoors during the peak mosquito activity times of dawn and dusk and to eliminate any sources of standing water near the animals (even check areas where rain water could accumulate, like old tires or bird baths)

Veterinarians who learn of potential WNV cases should contact the state veterinarian’s office at 360/902-1881.

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