Southwest Montana News

State and local health officials in Montana are reporting an increase in West Nile virus (WNV) activity across several counties, with the first three human cases of 2023 identified in Dawson, Rosebud, and Yellowstone counties. The individuals affected range from their late 30s to early 70s, including two males and one female, all of whom were hospitalized.

Additionally, this week saw two horses diagnosed with WNV infections in Hill and Pondera counties. Mosquito pools tested positive for WNV in Glacier, Lewis and Clark, and Toole counties. Earlier in the summer, positive tests were recorded in Blaine, Hill, and Phillips counties.

Infection can occur through bites from infected Culex mosquitoes. The risk of transmission to humans and horses is expected to continue through October or as long as mosquitoes remain active.

“With West Nile virus activity occurring in so many areas of the state right now, the best thing you can do to prevent infections is to protect yourself from mosquito bites,” said DPHHS Vectorborne Disease Epidemiologist Devon Cozart.

The risk is heightened during outdoor activities at dusk and dawn when female Culex mosquitoes are most active. The Environmental Protection Agency offers a search tool for finding EPA-registered insect repellents suitable for skin application. Permethrin can also be used on clothing and gear for additional protection.

While most people infected with WNV do not exhibit symptoms, about one in five may experience minor illness including headache, rash, body aches, joint pains, fatigue, vomiting, and diarrhea. Severe cases known as neuroinvasive West Nile occur in about one out of 150 infections leading to severe neurological symptoms or potentially fatal outcomes.

“All three human WNV cases reported this year were hospitalized which shows just how serious this disease can be,” said Cozart. “If you are concerned you have a West Nile virus infection please see your doctor.”

Currently there is no vaccine or targeted treatment available for humans; supportive care remains the primary option. A vaccine exists for horses which should be administered annually during springtime before mosquito season peaks.

Preventive measures include removing standing water weekly to reduce mosquito breeding grounds around homes. Additional mosquito bite prevention tips are outlined by health officials through what they call the "4 D’s of Mosquito Bite Prevention."

For more information on WNV protection and surveillance activities contact local health departments or visit the DPHHS WNV website page.