Big Sky Times

State and local health officials have reported the first detections of West Nile virus (WNV) in mosquitoes for summer 2024 across four Montana counties. Six mosquito pools in Blaine, Dawson, Prairie, and Wibaux counties tested positive for WNV. The detection in mosquitoes serves as an early indicator that activity is increasing within the state, raising the risk of illness among humans.

"Now is the time to take action against WNV if you haven’t already started thinking about mosquito bite prevention this season," said DPHHS Vectorborne Disease Epidemiologist Devon Cozart. "Infection can result in minor or severe illness, including death. Even minor forms of infection can leave individuals feeling ill and fatigued for weeks."

Infections occur 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.

Most people infected with WNV will not experience symptoms; however, 1 in 5 may experience minor illnesses such as headache, rash, body aches, joint pains, fatigue, vomiting, and diarrhea. Fatigue and body aches can persist for weeks following infection.

Approximately 1 in 150 human infections result in severe disease known as neuroinvasive West Nile. This form can cause neurological symptoms including disorientation, stupor, coma, paralysis, vision loss, and convulsions. WNV can be fatal or lead to long-term neurological complications such as paralysis.

Currently, there is no vaccine or targeted medication for WNV in humans aside from supportive care.

Horses are also susceptible to WNV infection. Horse owners are advised to contact their veterinarian for an annual vaccine to protect against the virus.

Preventing mosquito bites is crucial while spending time outdoors during summer months, especially at dusk and dawn when female Culex mosquitoes are most active. Permethrin insect repellent can be used on clothing and gear like tents. The Environmental Protection Agency provides a search tool to identify appropriate EPA-approved insect repellents that can be applied directly to the skin.

Mosquitoes carrying WNV rarely travel more than one mile from their breeding sites. To reduce mosquito presence around homes, it is important to regularly empty standing water at least once per week. For items like rain barrels, screens can be applied to restrict mosquito access.

For more information about WNV protection and surveillance activities visit https://dphhs.mt.gov/publichealth/cdepi/diseases/westnilevirus