Southwest Montana News

State and local health officials have announced the first detection of West Nile Virus (WNV) in mosquitoes in Montana this year, specifically from samples collected in Blaine County. As of now, there have been no reported cases of WNV in humans or horses for the current season.

The risk of WNV transmission through mosquito bites is expected to persist until October or as long as mosquitoes remain active in the state. Although no human cases were recorded in 2022, previous years have seen over 50 cases during a single summer. Last year, two horses tested positive for WNV, and infected mosquito pools were found in four counties: Lewis & Clark, Blaine, Phillips, and Dawson. Environmental conditions such as temperature and rainfall significantly affect mosquito populations and WNV activity.

Devon Cozart, a Vectorborne Disease Epidemiologist with DPHHS, stated that "Mosquito surveillance this year has identified a large proportion of active Culex species mosquitoes, the type of mosquitoes that can carry and transmit WNV." Cozart emphasized the importance of protecting oneself from mosquito bites to prevent diseases like WNV.

Protection is crucial during outdoor activities in summer, especially at dusk and dawn when female Culex mosquitoes are most active. Permethrin can be used on clothing and gear as an insect repellent. For skin application repellents, an Environmental Protection Agency search tool can help find suitable EPA-approved options.

Cozart also advised checking insect repellents for graphics indicating their effectiveness against mosquitoes and duration of protection.

The breeding range for mosquitoes carrying WNV is typically within one mile from their breeding site. To reduce mosquito presence near homes, it is recommended to empty standing water weekly. Rain barrels should be covered with screens to prevent access by mosquitoes.

Most people infected with WNV show no symptoms; however, about 20% may experience mild symptoms such as headache, rash, body aches, joint pains, vomiting, and diarrhea. Severe cases occur in approximately 1 out of 150 infections leading to neuroinvasive disease with serious neurological symptoms including disorientation and paralysis. These severe forms can be fatal or cause long-term complications.

Currently, there is no vaccine or specific treatment available for humans affected by WNV. However, a vaccine exists for horses which should be administered annually. Montanans are encouraged to consult their veterinarians regarding horse vaccinations against WNV.

For more information on protection measures and surveillance activities related to WNV, individuals are advised to contact local health departments or visit the DPHHS website dedicated to West Nile Virus information.