Local Situation

For the first time this season, Mesa County has a confirmed human case of West Nile virus. This resident may have been exposed to the positive mosquito out of state, but this case serves as a reminder to protect yourself from mosquitoes wherever you are.  

“To date in 2023, we have not had any Mesa County mosquitoes test positive for West Nile Virus; however, mosquitoes in surrounding counties have tested positive. Our partner, the Grand River Mosquito Control District, has ongoing mosquito surveillance to understand trends in our area and mitigate potential problem areas,” said Rachel Burmeister, Disease Surveillance and Emergency Response Program Manager for Mesa County Public Health. 

The public can view a heat map and look at specific mosquito traps on their website, grmcd.org

State Situation

So far this season, there are 22 confirmed human cases of West Nile virus in residents of 13 counties, including Delta. The state recently confirmed the first death associated with West Nile in Weld County.

Additionally, West Nile virus has been found in mosquitoes in nine of the 11 counties that have tested mosquitoes this season, including Adams, Arapahoe, Boulder, Delta, Denver, La Plata, Larimer, Pueblo, and Weld counties.

In 2022, Colorado had 206 reported human cases of West Nile virus, including 20 deaths.


“We’re entering September, which is traditionally the peak of West Nile illness. We want our residents to be safe and take extra precautions,” advised Burmeister.

There is no specific treatment for West Nile virus, so prevention is key. The best way to avoid getting West Nile virus is to avoid being bitten by mosquitoes. Increased outdoor activity can lead to increased exposure to mosquito bites so take some easy steps to protect yourself:

  • Use an EPA-approved insect repellent effective against mosquitoes. Look for one that contains DEET, Picaridin, IR3535, 2-undecanone, or oil of lemon eucalyptus.
  • Dress in long sleeves and pants when in areas where mosquitoes are active.
  • Avoid being outdoors at dusk and dawn; this is when mosquitoes are most active.
  • Drain and remove sources of standing water on your property.

Talk with a health care provider if you develop a fever with severe headaches or confusion. 


  • The West Nile virus season runs from May through October with case counts typically peaking in September. 
  • Most people who are infected with West Nile virus do not get sick. In fact, about 75-80% of cases are asymptomatic. For those who do experience symptoms, they can range from mild illness to severe encephalitis, which is inflammation of the brain. 
  • People who are over the age of 50 are at the highest risk for severe illness. 
  • This is not a condition that spreads from person-to-person.