by North Forty News Staff | NorthFortyNews.com
Health officials urge prevention as Culex mosquitoes test positive across region
WELD COUNTY, CO – The Weld County Department of Public Health and Environment (WCDPHE) has confirmed the first human case of West Nile virus (WNV) in a Weld County resident for the 2025 mosquito season. Last year, Weld County saw 15 confirmed cases.
Despite Culex mosquito numbers trending below the five-year average, health officials report that approximately 80% of trapped mosquitoes in the region still belong to the Culex genus—the species responsible for transmitting WNV. Mosquitoes in all three of Weld County’s monitored zones (Greeley/Evans/Kersey/LaSalle; Johnstown/Milliken/Platteville; and Firestone/Dacono/Fort Lupton) have tested positive for the virus.
West Nile virus symptoms typically appear between three and 14 days after infection. While most individuals show no symptoms, early signs can include fever, headache, nausea, vomiting, muscle aches, weakness, and rash. Severe cases—though rare—can result in neuroinvasive disease, which may be fatal. There is no vaccine or specific antiviral treatment for West Nile virus.
Weld County health officials are reminding residents that WNV remains a seasonal concern in Colorado and recommend the “Four D’s” to reduce risk:
- DRAIN standing water weekly from items such as tires, flowerpots, gutters, and toys.
- DUSK & DAWN are peak mosquito hours. Limit outdoor activity or take precautions.
- DEET or other EPA-registered repellents (like picaridin or oil of lemon eucalyptus) are effective when used as directed.
- DRESS in long sleeves, pants, and hats when outdoors in areas prone to mosquitoes.
Residents throughout Northern Colorado are encouraged to remain vigilant as WNV persists annually during the summer months.
For more information on prevention and WNV updates, visit weld.gov/go/zoonosis.