West Nile virus activity confirmed in Montana
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News from Montana DPHHS
MONTANA — 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 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. WNV can cause illness in humans after a bite from an infected Culex mosquito. The increased risk of transmission to humans is expected to continue through October, or as long as mosquitoes remain active in the state.
“Illness caused by WNV can vary significantly in severity,” said DPHHS Vectorborne Disease Epidemiologist Devon Cozart. “Although some people may not experience any symptoms at all, many people experience the onset of flu-like symptoms ... Severe, neurological cases of WNV also occur every year in Montana.”
Currently, there is no vaccine or targeted medication for WNV in humans, aside from supportive care.
The 4 Ds of Mosquito Bite Prevention include:
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: 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.
Contact your local health department or visit: https://dphhs.mt.gov/publichealth/cdepi/diseases/WestNileVirus for more information about WNV protection.
