West Nile Virus has been detected in Cascade County mosquitoes for the first time in 2026, and health officials say there are five simple steps every resident can take to stay protected.
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According to the Montana Department of Public Health and Human Services, a West Nile Virus positive mosquito sample was confirmed in both Lewis and Clark County and Cascade County. The Cascade County sample — a pool of adult Culex tarsalis mosquitoes collected southeast of Simms — was confirmed positive by the DPHHS lab in Helena on Aug. 20. Treatment has been conducted in the area where the sample was collected, and ongoing surveillance and monitoring efforts will continue.
No human infections have been reported in Cascade County in 2026, but health officials are urging residents to take precautions now, before exposure occurs.
The Ds — How to Protect Yourself:
The Cascade City-County Health Department recommends the following five steps:
1. DEET — Apply a repellent containing an EPA-registered active ingredient such as DEET and follow the directions on the package.
2. Dusk and Dawn — Mosquitoes are most active during these times. Avoid outdoor activities when possible.
3. Drain standing water — Standing water is the perfect breeding ground for mosquitoes. Drain gutters, pools, tires, buckets, and water bowls around your home.
4. Dress appropriately — Wear long-sleeved shirts, long pants, and socks when outdoors.
What to Watch For:
Health officials say approximately 80 percent of people infected with West Nile Virus will experience no symptoms at all. However, up to 20 percent can develop West Nile fever — a mild illness that generally resolves without treatment.
In rare cases — one in every 150 people — the virus can cause dangerous brain infections such as encephalitis or meningitis. Symptoms typically appear three to 14 days after exposure and may include high fever, stiff neck, mental confusion, muscle weakness, tremors, convulsions, coma, and paralysis.
Anyone experiencing these symptoms should see a healthcare provider immediately.
Contacts:
· Cascade City-County Health Department: Trisha Gardner — (406) 791-9261
· Cascade County Weed and Mosquito Control: Joshua Blystone — (406) 454-6920
