Mosquitoes Test Positive for West Nile Virus in Arapahoe County

Published on August 02, 2023

Mosquitoes at multiple locations in Arapahoe County have tested positive for West Nile virus. Two locations in Arapahoe County have mosquito populations that have tested positive for the virus, most recently near Heritage High School in Littleton. However, due to the growing number of positive test results across the Denver Metro area, Arapahoe County Public Health urges residents to take precautions at all outdoor locations to prevent mosquito bites. 

Seven counties in Colorado, including Arapahoe and neighboring Denver County, have confirmed West Nile-positive mosquitoes. Colorado saw its first case of West Nile virus in a human in late July. The season for high mosquito activity typically runs through September, so public health experts caution that our community has a while to go before West Nile risk peaks and declines. 

The good news is that, despite the risk posed by West Nile virus, prevention efforts to reduce the spread of the disease are working. Though mosquitoes near the Arapahoe County Fairgrounds tested positive for West Nile virus in early July, efforts to treat the surrounding area with insecticide were effective. Environmental health specialists conducted a follow-up test to the same pool where the prior positive mosquitoes were found, and the samples came back negative. 

Humans, birds, horses and other mammals can be exposed to West Nile virus via a bite from an infected mosquito. While symptoms in people infected with the virus are typically mild, there are steps you should take to limit exposure to the virus:

  • Wear an EPA-approved insect repellant, such as one that includes DEET. These repellants are proven safe and effective for all people ages 2 months and up, including those who are pregnant and breastfeeding. Learn more about tips for choosing and applying insect repellent for children.
  • Stay indoors at dawn and dusk when mosquitoes are most active. 
  • Avoid recreating around standing water sources, such as lakes and ponds. If you are camping, use mosquito netting. 
  • Wear clothes to protect against mosquitoes, such as long-sleeves and pants.
  • Drain standing water sources including puddles, gutters, flowerpots, tires, pool covers, boats and tarps. 
  • Prevent mosquitoes from getting indoors by utilizing an air conditioner or fans, rather than open windows, and if you do have any windows or doors with openings, utilize a screen. 
  • If you live on a property with a septic system, take steps to prevent mosquitoes by ensuring your tank is in good repair and any vents or openings are covered or sealed. 

Symptoms generally appear 2-14 days after exposure, with one in five people developing:

  • Fever
  • Body aches
  • Headache
  • Occasionally skin rashes and swollen lymph nodes

Less than 1 percent of people infected with West Nile Virus will develop severe symptoms that affect the nervous system. While these symptoms can occur in any person, people over 60 years of age are at higher risk, as well as those with certain medical conditions. Severe symptoms include:

  • Headache
  • Coma
  • High fever
  • Tremors
  • Neck stiffness
  • Muscle weakness
  • Confusion and disorientation
  • Paralysis

Mild symptoms of West Nile virus infection usually pass on their own. More information is available from the Colorado Department of Public Health and Environment.