UCHealth offers prevention tips as West Nile season returns to Colorado
Aurora, Colo. (June 26, 2025) – Health officials in Larimer County have detected Colorado’s first mosquitoes carrying West Nile virus this year, and UCHealth infectious disease experts warn that human infections from mosquito bites will likely follow in the coming weeks.
“The fact that we know there are positive mosquitoes now, means people are at risk for contracting West Nile virus,” said Dr. Daniel Pastula, chief of neuroinfectious disease and global neurology at UCHealth.
Most people who contract West Nile virus do not experience symptoms, Pastula said. However, about one in five may develop flu-like symptoms including fever, headaches, body aches, fatigue, vomiting, diarrhea and rash.
Roughly 1% of cases lead to West Nile neuroinvasive disease, in which the virus affects the nervous system, causing inflammation in and around the brain and spinal cord. People 50 years and older, as well as those who are immunocompromised, are at higher risk.
Symptoms of West Nile neuroinvasive disease can include seizures, coma, stroke-like symptoms such as muscle weakness or paralysis, vision loss and confusion. Some effects may be permanent. About 10% of neuroinvasive cases are fatal.
There is currently no antiviral medication to treat West Nile virus and no vaccine to prevent it.
“Among the people who recover from severe West Nile, many do have permanent neurological damage,” Pastula said. “Although it does seem to get somewhat better over time with intensive rehabilitation.”
Pastula says the five best ways to prevent mosquito bites are:
- Use insect repellents that contain DEET or other ingredients recommended by the EPA.
- If possible, wear loose-fitting, long-sleeved shirts and pants while outdoors.
- Avoid outdoor activities around dawn and dusk when mosquitoes are most active.
- Treat clothing with permethrin — an insecticide — before spending time outdoors.
- Drain standing water near your home to reduce mosquito breeding sites.
“If you don’t feel well or have a fever — and remember some mosquito bites in the days or weeks prior — contact your health care provider,” Pastula said.
About UCHealth
UCHealth is a nationally recognized nonprofit health system that pushes the boundaries of medicine through advanced treatments and clinical trials, improving health through innovation and providing unmatched patient care in the Rocky Mountain West. Investing $1.3 billion in community benefits including $570 million in uncompensated care each year, UCHealth is Colorado’s largest Medicaid provider and dedicated to the communities it serves. With the region’s only adult academic medical center, University of Colorado Hospital on the CU Anschutz Medical Campus, UCHealth includes 35,000 employees, 14 acute-care hospitals and hundreds of physicians across Colorado, Wyoming and western Nebraska.