State health officials have confirmed 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 reported that the deceased was an adult resident of Lafayette. In total, nine human cases of West Nile virus have been identified in residents across eight counties so far this year.
Mosquitoes carrying the virus have been detected in eight out of sixteen counties where mosquito testing has taken place this season. These counties include Adams, Arapahoe, Boulder, Broomfield, Denver, Jefferson, Larimer, and Weld.
“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 primarily transmitted through the bite of an infected mosquito. Symptoms usually develop three to fourteen days after being bitten and can include fever, severe fatigue, headache, body aches, skin rash, and swollen lymph nodes. Most people infected do not experience symptoms; however, some may develop a serious or potentially fatal illness. Individuals aged 60 years or older and those with certain medical conditions face a higher risk for severe disease.
Health officials recommend several preventive measures: use insect repellent containing DEET or other approved ingredients; limit outdoor activities during dawn and dusk when mosquitoes are most active; wear long sleeves, pants, and socks; remove standing water from yards weekly; treat undrainable water with larvicide; and ensure window and door screens are intact.
Weekly updates on case numbers as well as historical data trends can be found on the CDPHE West Nile virus webpage (https://cdphe.colorado.gov/west-nile-virus).
