NewsMontana News


First detection of West Nile Virus in Montana for 2023

West Nile Virus mosquito
Posted at 8:55 AM, Jul 26, 2023
and last updated 2023-07-26 10:55:55-04

GREAT FALLS — Public health officials said in a news release this week that the first West Nile Virus (WNV) detection of the year in Montana has been found in mosquitoes sampled from Blaine County.

No humans or horses have tested positive for WNV yet this season, according to the Montana Department of Public Health & Human Services.

Infected mosquitoes can transmit WNV when they bite, and increased risk of WNV transmission to humans and horses is expected to continue through October – or as long as mosquitoes are active in the state.

While no human cases of WNV were reported in Montana in 2022, in previous seasons Montana has reported more than 50 human cases in a single summer.

In 2022, two horses tested positive for WNV and positive mosquito pools were identified in four counties (Lewis & Clark, Blaine, Phillips, and Dawson). Environmental factors such as winter and summer temperatures and rainfall can heavily influence mosquito populations and WNV activity.

“Mosquito surveillance this year has identified a large proportion of active Culex species mosquitoes, the type of mosquitoes that can carry and transmit WNV,” said DPHHS Vectorborne Disease Epidemiologist Devon Cozart. “The best way to prevent mosquito-borne diseases, including WNV, is to protect yourself from mosquito bites.”

This is especially important while spending time outdoors in the summer, and during peak feeding activity times for female Culex mosquitoes, which is dusk and dawn. Permethrin is an insect repellent that can be utilized to treat clothing and gear, including tents.

“It is also a good idea to check your insect repellent for a graphic that indicates the repellent works on mosquitoes and the length of time it repels them,” Cozart said.

The mosquitoes that carry WNV rarely travel more than one mile from where they breed, so to keep mosquitoes away from the home, it’s important to regularly empty standing water once per week. For items such as rain barrels, a screen can be applied to the opening to restrict mosquito access. For other mosquito bite prevention tips, check out the "4 Ds" of mosquito bite prevention:

  • DEET-Apply repellent containing an EPA-registered active ingredient, such as DEET, and follow the directions on the package.
  • DUSK and DAWN-This is when mosquitoes are most active. Try to avoid outdoor activities during these times.
  • DRAIN STANDING WATER-Standing water is the perfect breeding ground for mosquitoes. Drain such areas around your home (gutters, pools, tires, buckets, water bowls, etc.).
  • DRESS APPROPRIATELY-Wear long-sleeved shirts, long pants, and socks.

Most people who become infected with WNV will not experience symptoms, but 1 in 5 do experience minor illness causing headache, rash, body aches, joint pains, vomiting, and diarrhea. However, about 1 in 150 WNV infections result in severe WNV disease, referred to as neuroinvasive West Nile. When neuroinvasive, WNV can cause severe neurological symptoms including disorientation, stupor, coma, paralysis, vision loss, and convulsions. WNV can be fatal or lead to long-term neurological complications. WNV can also cause severe neurological complications and death in horses.

Great Falls woman dies from West Nile Virus

Currently, there is no vaccine, treatment, or other targeted medication for WNV in humans. A vaccine is available for horses, who should be vaccinated once a year. Montanans are encouraged to contact their local veterinarian for questions about horses and WNV.


FOLLOW KRTV: Instagram | TikTok | Twitter