GREAT FALLS — Health officials have confirmed Montana’s first human case of West Nile virus this year in Cascade County. It is the county’s first known human case since 2018.
“From everything that we know, it does appear that this was locally acquired,” said Trisha Gardner, Cascade City-County public health officer.
WATCH Madison Collier's report below:
The case follows the recent detection of West Nile virus in a mosquito pool collected southeast of Simms. Gardner said the human case appears isolated and is not connected to a known outbreak.
However, she said Montana could see additional cases before the end of mosquito season.
“It was the first human case reported. However, I would expect we’ll probably see additional ones,” Gardner said.
She said West Nile virus is spread through the bite of an infected mosquito. Surveillance across the state includes trapping mosquitoes and testing them in groups, known as pools, to determine where the virus is circulating.
West Nile activity can vary significantly from year to year, ranging from isolated cases to larger outbreaks. Gardner says the risk generally increases during the summer and can continue into fall while mosquitoes remain active.
According to the Montana Department of Health and Human Services, about 80% of infected people never develop symptoms and may not know they have the virus. About 20% develop symptoms such as fever, headaches, body aches, joint pain, vomiting, diarrhea or a rash.
Symptoms typically begin two to 14 days after a mosquito bite. Most people with mild illness recover, although fatigue and weakness can continue for weeks or months.
Fewer than 1% of infected people develop a severe illness affecting the nervous system. The agency recommends seeking immediate medical attention for symptoms including a high fever, neck stiffness, confusion, muscle weakness or tremors.
“If you’re over 50, but particularly if you’re over 70, even more so, they are the most at risk,” Gardner said, adding people with certain underlying health conditions face a greater risk of severe illness.
Cascade County will continue mosquito surveillance and treat larvae and adult mosquitoes as needed.
The Montana DPPHS recommends remembering the four Ds:
- Dress in long sleeves, long pants, shoes and socks when mosquitoes are active.
- Drain standing water around homes and regularly replace water in items such as birdbaths.
- Use an insect repellent containing DEET, picaridin or another EPA-registered ingredient.
- Avoid spending time outside around dawn and dusk, when mosquitoes that spread West Nile are most active.
For more information and current West Nile virus data, visit the CDC’s website.
