West Nile Virus Confirmed in Montana

DPHHS urges Montanans to take increased caution against mosquito bites this summer.

State and local health officials confirmed the first detections of West Nile virus (WNV) in Montana for summer 2025. WNV activity appears to be widespread across the state, and the Department of Public Health and Human Services (DPHHS) is urging all Montanans to take increased precautions against mosquito bites.

Four mosquito pools have tested positive for WNV, including three in Lewis and Clark County and one in Cascade County. Detection of WNV in mosquitoes is an early indicator that activity is increasing within the state, elevating the risk of human illness.

Sheridan, Custer, and Daniels Counties have each reported one confirmed case of WNV in horses, t...