Date: July 01 2021

Contact: Jon Ebelt, Public Information Officer, DPHHS, (406) 444-0936, (406) 461-3757,
                Chuck Council, Communications Specialist, DPHHS, (406) 444-4391, (406) 461-8367,

Health Officials Suggest Steps to Prevent West Nile Virus

State and local public health officials are reminding Montanans to take steps to avoid mosquito bites and prevent infection from West Nile Virus (WNV). In Montana, WNV season usually begins in July and ends in October, as this is when the mosquitoes responsible for it emerge.

“As we head into West Nile Virus season all Montanans are encouraged to take the necessary precautions,” Department of Public Health and Human Services (DPHHS) epidemiologist Erika Baldry said. “There was only one case in 2020, and we want to keep it that way. However, the reality is Montana averaged 23 human cases over a three-year period prior to 2020. We urge Montanans and those visiting the state to learn the necessary steps anyone can take to avoid WNV.”

The best way to prevent mosquito-borne diseases, including WNV, is to avoid mosquito bites. While mosquitoes found in Montana are unable to transmit diseases like Zika virus, they can transmit WNV. The virus can also infect horses and birds, with birds serving as the source of infection for most mosquitoes who then pass the virus along to humans by biting them.

During the 2020 mosquito season, there was one reported positive human case in Custer County and one positive equine case in Rosebud County. One county, Valley, reported a positive mosquito pool. Montana has reported a total of 14 WNV-related deaths since surveillance began in 2002.

The average number of human cases reported in the three years prior (2017-2019) was 23 cases, while the average number of equine cases reported in the three years prior (2017-2019) was 20 cases. This includes an outbreak in 2018 where a total of 51 human cases and 50 equine cases were reported.

When infected with WNV, about 4 out of 5 people will not have symptoms and will develop immunity after clearing the infection. Among the 1 in 5 individuals who develop illness, they will generally experience mild symptoms that may include: headache, body aches, joint pain, vomiting, diarrhea, or a rash.

Serious symptoms can develop in rare cases with fewer than 1 in 100 of those infected developing infections in or around the brain, also known as neuroinvasive disease. The single case reported in 2020 was neuroinvasive disease. Currently, no vaccine or specific treatment exists for a person at risk or ill with WNV. If someone develops any of the symptoms listed above, they should see their healthcare provider for evaluation and care.

As mentioned, humans are not the only ones that can be infected with WNV. Last year, Montana had one case of WNV reported in a horse. A vaccine for horses is available and highly recommended.

The 4 D’s of WNV prevention should be followed to reduce the chance of mosquito bites.

  1. DEET: Use insect repellent such as DEET or picaridin.
  2. Drain: Drain standing water around your house to prevent mosquito breeding.
  3. Dawn/Dusk: Mosquitoes are most active during dawn and dusk. Stay inside or take precautions to prevent mosquito bites during these times.
  4. Dress: When possible, wear long sleeved shirts and pants to protect yourself from bites.

For more information about WNV, please visit the DPHHS website at: