Weld County Culex mosquitoes test positive for West Nile Virus

Published on July 13, 2022

Mosquitoes in petri dish

Weld County, Colorado — The Weld County Department of Public Health and Environment (WCDPHE) continues to take proactive measures in monitoring for West Nile Virus (WNV) after mosquitoes recently trapped in the county tested positive for WNV.

The number of Culex mosquitoes, which carry WNV, also is increasing, with the trapped Culex mosquito count in 2022 higher than the 5-year average. "The increasing hot weather and afternoon thundershowers have created favorable conditions for the Culex mosquito,” said Mark Lawley, WCDPHE Executive Director.

A WCDPHE contractor monitors mosquito traps weekly in 3 zones of Weld County: Greeley, Evans, Kersey, and LaSalle (Zone 1); Johnstown, Milliken, and Platteville (Zone 2); and Firestone, Dacono, and Fort Lupton (Zone 3). Mosquitoes trapped in Zones 2 and 3 have tested positive for WNV. Currently, there are no human cases of WNV in the county. However, health officials expect this to change as the Culex mosquito season carries on in July and August. “The public needs to be vigilant because West Nile Virus has a permanent summer presence in Colorado,” Lawley said.

WNV symptoms can appear 3-14 days after an infection and can include fever, headache, nausea and vomiting, muscle aches and weakness, and rash, but most infected people don’t exhibit any symptoms. If symptoms develop, see a health care provider 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 4 “Ds” 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.
  • DRESS in long sleeves and pants, and a hat in areas where mosquitoes are active.
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