Weld County Culex mosquitoes test positive for West Nile virus

Published on July 23, 2026

A mosquito on a leaf.

Mosquitoes trapped in Weld County have tested positive for West Nile virus (WNV). A health department contractor monitors mosquito traps weekly in three areas of Weld County: the Greeley, Evans, Kersey, and La Salle area (Zone 1); the Johnstown, Milliken, and Platteville area (Zone 2); and the Firestone, Dacono, and Fort Lupton area (Zone 3). Mosquitoes trapped in Zone 2 have tested positive for WNV.

The number of Culex mosquitoes, which carry WNV, is below average for this time of year. Currently, there are no reported human cases of WNV in Weld County. However, officials at the Weld County Department of Public Health and Environment expect this to change as the Culex mosquito season expands with the hot weather in July and August. The department will continue to take proactive measures to monitor the virus.

“Increasingly hot weather often creates favorable conditions for the Culex mosquito that carries West Nile virus,” said Jason Chessher, executive director of the Weld County Health Department. “The public needs to remain vigilant because West Nile virus has a permanent summer presence in Colorado.”

West Nile Virus symptoms can appear three to 14 days after an infection. Initial symptoms can include fever, headache, nausea and vomiting, muscle aches and weakness, and rash, but most infected people don’t exhibit any symptoms. If a person develops symptoms, they should see a health care professional immediately. There are no medications to treat or vaccines to prevent WNV infection. Less than 1% of infected people develop a serious, sometimes fatal, neuro-invasive illness. Health officials recommend following the four “D’s” to prevent mosquito bites:

  • DRAIN standing water around your house weekly. Remember to drain water from tires, cans, flowerpots, clogged rain gutters, rain barrels, toys, and puddles.

  • DUSK and DAWN are when mosquitoes are most active. Limit outdoor activities and take precautions to prevent mosquito bites during these times.

  • DEET is an effective ingredient to look for in insect repellents. Other repellents containing picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol are also effective against mosquitoes. Always follow the product label instructions carefully.

  • DRESS in long sleeves and pants, and a hat, in areas where mosquitoes are active.

For more information about preventing mosquito bites and WNV, including a map of mosquito zones and trapping and testing updates, visit www.weld.gov/go/zoonosis.

Tagged as:
Back to top