First Confirmed Equine Case of West Nile Virus in Montana for 2017


Last week, the Montana Department of Livestock confirmed the first equine case of West Nile Virus for the year in Yellowstone County. This follows detection of the virus in mosquito surveillance pools from Custer, Prairie, Blaine, Hill, and Phillips Counties.  The disease also affects people, and public health officials are investigating several human cases.  Montana typically sees cases of West Nile Virus through late summer and into fall.


West Nile Virus affects humans, equines, and birds.  It is spread through the bites of infected mosquitos; horses cannot transmit the virus directly to people. 


Dr. Tahnee Szymanski, Assistant State Veterinarian, says, “There is no direct treatment for the virus, but vaccination is highly effective in preventing disease.  Horses that are vaccinated rarely die or are euthanized because of the disease .” Horse owners should be aware of the typical signs of West Nile Virus which include:

  • Fever, loss of appetite and depression;
  • Incoordination or weakness of the hind limbs;
  • Muscle or muzzle twitching, drooling.


Syzmanski says, “Vaccination is typically administered in the spring, but may offer some protection even this late in the season.  Work with your veterinarian to determine if your horse could still benefit from a vaccination.” In the meantime, topical insecticides and eliminating standing water may help decrease your horse’s exposure to mosquitos. The mosquitos that carry West Nile Virus are most active at dawn and dusk, so consider keeping your horses off of irrigated pastures and away from water sources during those times of day. 


The mission of the DOL is to control and eradicate animal diseases, prevent the transmission of animal diseases to humans, and to protect the livestock industry from theft and predatory animals. For more information on the department, visit

 Picture: Pixabay

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