State health authorities have reported the first human death from West Nile virus in Colorado for 2025. The Colorado Department of Public Health and Environment (CDPHE) and Boulder County Public Health confirmed that an adult resident of Lafayette died after contracting the virus. As of now, nine human cases have been identified across eight counties.
Mosquitoes carrying West Nile virus have been detected in Adams, Arapahoe, Boulder, Broomfield, Denver, Jefferson, Larimer, and Weld counties this season. Out of 16 counties testing mosquitoes so far, half have found evidence of the virus.
“We are deeply saddened to confirm the first West Nile virus-related death in our state this year. This tragic loss underscores the serious nature of this virus and why personal prevention is so vital,” said Dr. Ned Calonge, Chief Medical Officer at CDPHE. “I cannot stress enough the importance of taking simple, effective steps — like using repellant and draining standing water — to protect yourself and your loved ones from West Nile virus infections.”
West Nile virus is most often spread through mosquito bites. Symptoms usually develop three to 14 days after exposure and may include fever, fatigue, headache, body aches, rash, or swollen lymph nodes. Most people do not experience symptoms; however, some can develop severe illness that may be fatal. People aged 60 or older and those with certain medical conditions face a higher risk for complications. Health officials recommend consulting a provider if someone develops a fever with severe headaches or confusion.
The CDPHE recommends several preventive measures: using insect repellent containing DEET or other approved ingredients; limiting outdoor activity during dawn and dusk when mosquitoes are most active; wearing long sleeves and pants; removing standing water from yards weekly; treating undrainable water with larvicide; and maintaining window and door screens.
For ongoing updates about West Nile virus activity in Colorado as well as historical data trends, residents can visit the CDPHE West Nile virus webpage.
