It’s Not Too Late to Vaccinate Horses against West Nile

Wyoming animal health officials encourage owners to vaccinate horses against the potentially deadly virus.
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As fall approaches, horse owners might be tempted to believe the West Nile virus (WNV) threat is waning. However, cases of WNV in horses continue to be reported throughout the state of Wyoming. At least 15 have been diagnosed by the Wyoming State Veterinary Laboratory this season, according to Wyoming State Veterinarian Jim Logan, DVM.

“The vector season for West Nile virus can last until a hard frost kills or inactivates the vectors,” warns Logan. Thus, the Wyoming Livestock Board veterinary staff recommends that owners vaccinate their horses if they have not done so already.

Horses are far more affected by the WNV than other livestock and domestic animals. 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. Equine mortality rate can be as high as 30-40%.

Because mosquitoes are the main source of WNV transmission, controlling mosquito populations and preventing horses from being exposed to them can help. However, the WNV vaccine is still the best method of prevention, providing over 90% protection, the livestock board said. While the Wyoming Livestock Board veterinary staff recommends vaccinating all foals and horses against the disease in the spring, prior to peak mosquito levels, owners who have not yet vaccinated this year should still consider doing so, due to the rising number of recently reported cases around the state

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