First West Nile mosquito found in Larimer County

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Mosquitoes from a trap in southeast Fort Collins, near Timberline and Carpenter, have tested positive for West Nile virus, according to officials at the Larimer County Department of Health and Environment. The trap with positive mosquitoes was collected on June 5, more than a month earlier than in a typical year.

The early appearance of infected mosquitoes in Larimer County and two other counties (Weld and Delta) suggests that this could be a summer of high West Nile virus activity and increased human infections, health officials warn.

Culex mosquitoes, the ones that carry West Nile virus, increase in number as temperatures rise. In hot weather, mosquitoes grow from larvae to adult mosquitoes very quickly, increasing their numbers. WNV outbreaks often occur in drought years.

West Nile virus is transmitted to humans through the bite of an infected mosquito. Infections can occur without symptoms or can cause illness ranging from mild to severe, and in some cases, can lead to chronic disability or death. At increased risk of serious illness from West Nile infection are people over 50, solid organ transplant recipients, and people with weakened immune systems. However, even healthy people can become ill from the bite of a WNV-infected mosquito.

The surest way to prevent getting West Nile virus is to avoid mosquito bites. The Health Department strongly urges Larimer County residents to use mosquito repellent when outside at peak hours, between dusk and dawn, when Culex mosquitoes are most active, even though the number of mosquitoes is relatively low right now. Repellents that have been proven to be effective against West Nile virus-carrying mosquitoes include ones that contain DEET, Picaridin, Oil of Lemon Eucalyptus (with active ingredient PMD, or p-menthane diol) or IR3535.

For more tips on what you can do to prevent West Nile virus, or on repellent use, visit the county health department at or the Colorado Department of Public Health and Environment West Nile virus info site at