West Nile Virus Activity Continues in Northeast Montana

West Nile virus activity is continuing across Montana, and mosquito surveillance is underway in Valley County.

While no mosquitoes collected in Valley County had tested positive for West Nile virus as of the latest local surveillance report, health officials are continuing to monitor the county because the virus has been detected elsewhere in northeast Montana.

Montana health officials say more than 15,000 Culex mosquitoes—the species that can carry West Nile virus—have been collected and tested across 30 Montana jurisdictions this season.

Statewide, 12 mosquito pools have tested positive, including four in Phillips County. Positive mosquito pools have also been identified in Roosevelt, Blaine, Dawson, Rosebud and Cascade counties.

And there are now confirmed infections in people.

McCone County reported its first human case of West Nile virus since 2023 last week. The patient was briefly hospitalized and is recovering at home.

The McCone County Health Department says the person had been exposed to mosquitoes in Roosevelt and Richland counties.

Montana has also reported a human case in Cascade County and West Nile infections in horses in Beaverhead, Hill and Yellowstone counties.

For Valley County residents, health officials say the lack of a positive mosquito pool does not mean there is no risk.

Montana's Department of Public Health and Human Services says mosquito surveillance serves as an early warning system, and the active West Nile season continues through October—or as long as mosquitoes remain active.

West Nile virus is primarily spread by the bite of an infected Culex mosquito.

Most people infected with West Nile virus don't develop symptoms. About one in five develop a mild illness that can include headache, fever, rash, body aches and fatigue.

About one in 150 infections can result in serious neurological illness, including encephalitis or meningitis.

There is no human vaccine or specific treatment for West Nile virus, so prevention remains important.

Health officials recommend the four D's:

DEET—use an EPA-registered mosquito repellent.

DRAIN—remove standing water around homes and businesses.

DAWN and DUSK—take extra precautions because mosquitoes that transmit West Nile are most active around those times.

And DRESS—wear long sleeves, long pants and socks when spending time outdoors.

With mosquito activity continuing into the fall, Valley County residents are being encouraged to continue taking precautions—even though no positive mosquito pools have been identified in the county so far.