West Nile Virus Mosquito Surveillance Continues in Valley County

Mosquito surveillance has identified 12 total West Nile Virus (WNV) positive mosquito pools this season, with 4 located in Phillips County. No mosquitoes have been identified with the virus in Valley County. Over 15,000 Culex species (WNV carrier) mosquitoes have been collected across 30 jurisdictions for WNV testing in Montana.

The first human and horse cases of WNV for the 2026 summer season were reported this week. The horse resides in Beaverhead County, but had recent travel out of state. The human is a non-neuroinvasive case out of Cascade County with no recent out-of-state travel. The seven counties with WNV activity are orange in the map shown.

West Nile Virus PREVENTION 

The best way to prevent WNV infection is to prevent getting bitten by mosquitoes. You can take steps to minimize your possibility of encountering WNV by remembering the 4 D’s:

DRESS: Wear shoes, socks, long pants, and a long-sleeved shirt when outdoors for long periods of time or when mosquitoes are most active. Clothing should be light colored and made of tightly woven materials to keep mosquitoes away from the skin.

DRAIN: Reduce the amount of standing water in or near your property by draining and/or removing it. Mosquitoes may lay eggs in areas with standing water. Necessary standing water should be changed (e.g. birdbath), moved (e.g. adding a fountain to a pond), or covered (e.g. putting a mesh screen over a water barrel).

DEET: For additional protection from mosquitoes, use an insect repellent containing DEET (N,N-diethyl-m-toluamide) or picaridin (KBR 3023). Other insect repellents such as oil of lemon eucalyptus and IR3535 are also registered by the EPA but may be less effective than products containing DEET. It is important to follow the product guidelines when using insect repellent.

DAWN/DUSK: Whenever possible, avoid spending time outside at dawn and dusk. This is when the mosquitoes that spread WNV are most likely to bite. If you keep windows open in your home, make sure that you are using well-fitting screens without holes or tears, to prevent mosquitoes from coming inside.