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For Immediate Release

August 23, 2013
Steve Merritt
Public Information Officer
Montana Department of Livestock

State Vet Issues West Nile Advisory for Equine Owners

Animal health officials with the Montana Department of Livestock are advising equine owners in parts of the state to be on the lookout for West Nile virus after positive mosquitoes were found in eight counties last week.

Positive mosquitoes were found in Cascade, Blaine, Hill, Lewis & Clark, Prairie, Sheridan, Phillips and Teton Counties.

While the mosquito season is winding down with fall approaching, state veterinarian Dr. Marty Zaluski said it’s not too late to booster equines that have already been vaccinated.

“We know that vaccination is highly protective against West Nile, and if your horse has already been vaccinated, a booster may provide additional protection this late in the season,” he said. “That’s why it’s important to work with your local veterinarian to develop a core vaccination program.”

Greg Johnson, veterinary entomologist for Montana State University’s Department of Animal & Range Sciences, said topical insecticides may provide some immediate protection.

“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.”

Equine owners can also take other measures to reduce exposure:

  • Eliminate potential breeding sites (old receptacles, tires, and containers) and areas of standing water;
  • Thoroughly clean livestock watering troughs weekly;
  • Keep horses indoors during peak mosquito activity periods of dusk to dawn;
  • Avoid using lights, when possible, that may attract mosquitoes inside stables during the evening and overnight.

Zaluski said it’s also important to be familiar with signs of the disease, which causes encephalitis, or swelling of the brain, and can be difficult to distinguish from other neurological diseases like sleeping sickness and rabies. Some of those signs include:

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

“If you see anything suspicious, contact your veterinarian,” Zaluksi said. “Developing a good working relationship with your vet is the quickest, easiest way to stay on top of things like West Nile and other diseases.”

Montana had seven cases of WNV in equines last year; prior to that, the last reported case was in 2009.

Based on state and national figures, roughly one-third of the unvaccinated horses that contract the disease die or must be euthanized.

For additional information about WNV in horses, please see American Association of Equine Practitioners web site.

For additional information about WNV in humans, please see the Department of Public Health & Human Services web site.