West Nile Virus-positive mosquito samples confirmed in Cascade County

West Nile Virus mosquito
Posted at 4:01 PM, Aug 15, 2023

The Cascade County Weed & Mosquito Division has detected its first West Nile Virus (WNV)-positive mosquito samples of 2023.

The agency said in a news release on Tuesday, August 15, 2023, that two WNV positive samples of adult Culex tarsalis mosquitos were collected from the northern and northwest city limits of Great Falls on Thursday, August 10th.

The samples were confirmed positive by the lab at the Montana Department of Public Health & Human Services in Helena on August 14th.

Mosquito control treatments were applied in the affected areas on the evening of August 10, and the Weed & Mosquito Division continues monitoring in those areas and throughout Cascade County.

There have been no known human infections of WNV detected in Cascade County in 2023, but the agency says that residents are "strongly encouraged" to take steps to protect themselves.

Last month, the first West Nile Virus detection of the year in Montana was found in mosquitoes sampled from Blaine County.

No humans or horses have tested positive for WNV yet this season, according to the Montana Department of Public Health & Human Services.

While no human cases of WNV were reported in Montana in 2022, in previous seasons Montana has reported more than 50 human cases in a single summer.

The best defense against WNV is bite prevention. To protect yourself, use the 5 Ds:

  • DEET - Apply repellent containing an EPA-registered active ingredient, such as DEET, and follow the directions on the package.
  • DUSK and DAWN - This is when mosquitoes are most active. Try to avoid outdoor activities during these times.
  • DRAIN STANDING WATER - Standing water is the perfect breeding ground for mosquitoes. Drain such areas around your home (gutters, pools, tires, buckets, water bowls, etc.).
  • DRESS APPROPRIATELY - Wear long-sleeved shirts, long pants, and socks.

The severity and symptoms of WNV can vary widely. About 80% of persons infected experience no symptoms, but up to 20% of infected persons can develop a mild illness called West Nile fever. Fever generally resolves itself without treatment, but dangerous brain infections such as encephalitis or meningitis can develop in 1 out of 150 people.
Symptoms usually appear within 3 to 14 days after exposure and may include headache, rash, high fever, stiff neck, mental confusion, muscle weakness, tremors, convulsions, coma, and paralysis. Individuals who develop any of these symptoms should see their healthcare provider immediately.

2019: Great Falls woman dies from West Nile Virus

Currently, there is no vaccine, treatment, or other targeted medication for WNV in humans. A vaccine is available for horses, who should be vaccinated once a year. Montanans are encouraged to contact their local veterinarian for questions about horses and WNV.