West Nile Virus confirmed in Montana, health department says

State and local health officials confirmed the first detections of West Nile virus in Montana for summer 2026, the Department of Public Health and Human Services said Wednesday in a news release.

Two mosquito pools tested positive for West Nile Virus in Roosevelt County, and health officials said the virus will likely spread across the state.

They are urging all Montanans to take increased precautions against mosquito bites, although no West Nile infections have been reported in humans or horses yet this summer, the news release said.

“Detection of WNV in mosquitoes is an early indicator that activity is increasing within the state, elevating the risk of human illness,” the news release said.

West Nile Virus can cause illness in humans, and the increased risk of transmission to humans is expected to continue through October or as long as mosquitoes remain active in the state.

“The risk of severe illness is a serious concern,” said DPHHS vectorborne disease epidemiologist Devon Cozart in a statement. “Every year, some Montanans experience neurological complications that can cause permanent disability or death.”

Health officials recommend people use insect repellent and take other measures to prevent bites.

• DEET: Use insect repellent containing effective ingredients such as DEET or picaridin. To verify the effectiveness of insect repellent, go to the EPA’s website: www.epa.gov/insect-repellents.

• Drain: Drain standing water around the house to prevent mosquito breeding.

• Dawn/Dusk: Mosquitoes are most active during dawn and dusk. Stay inside or take extra precautions to prevent mosquito bites during these times. If doors or windows are left open in the summer, make sure they’re fitted with screens to keep mosquitoes out of the house.

• Dress: When possible, wear long-sleeved shirts and pants to protect against bites.

There is no vaccine or targeted medication for West Nile Virus in humans, the news release said. One-in-five people experience mild symptoms, including headache, rash, body aches, joint pains, fatigue, vomiting and diarrhea, according to the health department. One-in-150 infections results in severe disease and can cause neurological symptoms, including disorientation, stupor, coma, paralysis, vision loss and convulsions.