West Nile Virus Identified in Weld County Culex Mosquitoes

Published on August 02, 2019

Culex mosquito

Weld County — The risk for human infection from West Nile Virus (WNV) has increased due to mosquitoes in the Greeley/Evans area testing positive for WNV. Currently there are no human cases of WNV reported in Weld County. However, this is expected to change in the ensuing weeks as the Culex mosquito — the mosquito species that carries WNV —continues to emerge. “Our hot and humid August weather, followed by afternoon thunderstorms, creates the perfect conditions for the Culex mosquito,” said Mark E. Wallace, MD, MPH, Executive Director of the Weld County Health Department. “It’s extremely important to avoid getting bit by mosquitoes.” Many municipalities have established mosquito control programs, but “the public needs to be aware and prevent mosquito bites because this illness has a permanent summer presence in Colorado,” Wallace said.

The Health Department determined the vector index — a calculation to determine human risk for WNV infection — is still low. However, the vector index is likely to increase in the ensuing weeks, which means the risk for human infection also will increase. A vector index that exceeds 0.50 shows a need for increased awareness; a vector index of 0.75 or higher indicates a significant risk for human infection. This past week, the Greeley and Evans area (Zone 1 trapping area) tested at 0.33. The other Weld County mosquito trap zones have tested negative for WNV. “From a public health surveillance perspective, we are expecting the Culex mosquitoes and risk for WNV to increase across Weld County,” Wallace said.  

West Nile Virus symptoms can appear 3 to 14 days after 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, he or she should see a health care professional immediately. There are no medications to treat or vaccines to prevent WNV infection. Less than one percent of infected people develop a serious, sometimes fatal, neuroinvasive 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 also are effective against mosquitoes. Always follow label instructions carefully.
  • DRESS in long sleeves and pants where mosquitoes are active.