Human Cases of West Nile Virus Reported in Larimer County

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This week, the Larimer County Department of Health and Environment (LCDHE) reported the first two cases of West Nile virus in Larimer County residents this season. The individuals reside in Berthoud and Fort Collins.

West Nile disease is a viral infection spread to people by bites from infected Culex mosquitoes. Symptoms can range from none at all to severe illness. Most people who are infected don’t have any symptoms, but some will develop West Nile fever which may progress to severe neuroinvasive infection. This may lead to hospitalization, critical illness, chronic disability, or even death.

LCDHE works with local cities and towns, a mosquito abatement company (Vector Disease Control International), and Colorado State University to monitor and assess the risk of West Nile virus to Larimer County residents. Trapping mosquitoes to monitor for West Nile virus risk began in June in Larimer County, confirming that mosquitoes, including those that carry West Nile virus, are abundant in many areas of the county. Human cases of West Nile virus usually peak in August and September every year.

West Nile virus can be prevented, and residents are reminded to take precautions to avoid being bitten by mosquitoes.  In addition to community efforts, such as larviciding, reducing water where mosquitoes can breed, and spraying for adult mosquitoes, individuals can use the 4 D’s to help prevent West Nile virus disease:

  • Defend – Use an EPA-registered mosquito repellent that has been proven to be effective against West Nile virus-carrying mosquitoes. DEET, Picaridin, Oil of Lemon Eucalyptus and IR3535 are good choices.
  • Dusk to Dawn – Avoid exposure during peak Culex mosquito feeding times, from dusk through dawn.
  • Dress – Wear long sleeves and pants to keep mosquitoes from biting.
  • Drain – Remove standing water in your yard or garden to minimize mosquito breeding areas.

For more tips on what you can do to prevent West Nile virus, visit