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Sunday, January 25, 2015

First West Nile virus-infected mosquitoes of 2010 confirmed in Larimer County


Mosquitoes from one trap in southeast Fort Collins have tested positive for West Nile virus, according to officials at the Larimer County Department of Health and Environment. The mosquitoes were collected the week of July 19 – 23.

“The numbers of Culex mosquitoes, the kind that carry West Nile virus, are increasing rapidly in this hot weather,” said Dr. Adrienne LeBailly, director of the Larimer County Department of Health and Environment.

Mosquito traps are placed each week in Fort Collins, Loveland, Timnath, and Berthoud. Mosquitoes from some of the traps are then tested in groups called “pools” for the presence of West Nile infection.

“It’s already been a week since many of those mosquitoes were trapped, so it’s likely that the number of infected mosquitoes has risen since then,” LeBailly added. “Especially for the next six weeks, it’s very important to wear repellent between dusk and dawn, when Culex mosquitoes are most active.”

The continuing hot weather can be expected to have an impact on the growth of West Nile virus. In hot weather, mosquitoes grow from larvae to adult mosquitoes very quickly, increasing their numbers. Higher nighttime temperatures will likely lead to more mosquito activity that can result in transmission of the virus to humans.

West Nile virus is a disease transmitted to humans through the bite of an infected mosquito. It can cause mild to severe illness and, in some cases, leads to chronic disability or death. Six confirmed cases of human West Nile virus (WNV) infection have been reported in Colorado through July 26; one each from Larimer, Moffat, Prowers, Pueblo, Sedgwick and Weld Counties. Human case reports tend to lag three to four weeks behind the time the person is actually bitten by an infected mosquito, so these numbers reflect what was happening nearly a month ago.

West Nile virus is usually first detected in mosquitoes in this area in mid-July. 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, all persons who are not adequately protected are at risk of being bitten by an infected mosquito.

The surest way to prevent getting West Nile virus is to avoid mosquito bites. Preventive steps you can take include:

  • Use a mosquito repellent that has been proven to be effective against West Nile virus-carrying mosquitoes. Ones that contain DEET, Picaridin, Oil of Lemon Eucalyptus (with active ingredient PMD, or p-menthane diol) or IR3535 are good choices.
  • Use mosquito netting over baby carriers and strollers.
  • Keep exposed skin covered or use a repellent when out at prime Culex mosquito-biting hours, between dusk and dawn.
  • Use a powerful fan while sitting on your deck or patio to keep mosquitoes away.
  • Drain standing water in your yard or in your garden.
  • Add mosquito-eating minnows or mosquito “dunks” to ornamental ponds with still water.
  • Keep window screens repaired.

For more tips on what you can do to prevent West Nile virus, or on repellent use, visit: www.Larimer.org/health or call 498-6700.

City of Fort Collins West Nile virus website:

For information on repellent use, go to

Colorado Department of Public Health and Environment West Nile virus info

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