Montana Confirms Equine WNV Cases

Montana Confirms Equine WNV Cases

Topical insecticides can help provide more immediate protection against the disease.

Photo: The Horse Staff

The Montana Department of Livestock is reminding equid owners statewide to be on the lookout for West Nile virus (WNV) after numerous cases were confirmed in horses recently.

“We’ve had nine positive cases confirmed in the past five days, so the threat is definitely there,” said State Veterinarian Marty Zaluski, DVM.

Zaluski said equid owners should be familiar with clinical signs of the disease, which can be difficult to distinguish from other serious neurologic diseases like sleeping sickness and rabies. Some of those signs include:

  • Loss of appetite and depression;
  • Fever;
  • Incoordination (ataxia) or weakness of the hind limbs;
  • Muscle or muzzle twitching;
  • Convulsions; and
  • Inability to swallow.

“If you notice any of these, or other, unusual symptoms, contact your veterinarian,” Zaluski said. “There is no direct treatment for the virus, but with early detection and supportive veterinary care, some infected horses will recover.”

Vaccination has been shown to be highly effective in preventing the virus. It requires an initial vaccination and then a booster, and is typically administered in the spring. Your veterinarian can help determine if an initial vaccination this late in the season would provide adequate protection.

Seven of the recently confirmed cases had not been vaccinated against the disease or their WNV vaccine was not current; four of those horses either died or were euthanized.

In the meantime, topical insecticides can help provide more immediate protection, said Greg Johnson, PhD, veterinary entomologist for Montana State University's Department of Animal and Range Sciences.

"I'd suggest a permethrin insecticide treatment to suppress mosquito blood feeding," Johnson said. "A product like Brute pour-on (10% permethrin) can be applied as a wipe-on, while Gardstar (40% permethrin) can be mixed with water and applied as a low volume spray or a wipe-on. "

A single application can provide up to seven days of protection, he said, and "using it for a couple of weeks might be enough to get you through the rest of the mosquito season."

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