West Nile Virus

These viruses are transmitted to people and animals by bites from infected mosquitoes. Only certain species of mosquitoes carry the virus and very few mosquitoes actually are infected. In Colorado, these viruses are transmitted to people by a species called Culex tarsalis, a medium-sized mosquito that feeds in the few hours around dawn and dusk. During the day, they rest in shady, secluded areas, such as under porches, roof overhangs, tall grass, shrubs, and storm sewers. They breed in almost any source of standing water, including irrigated fields, old tires, hoof prints, flowerpots, tree holes, or any puddle of water that lasts for more than a few days.

These mosquitoes live in lower elevations in Colorado.

Most people who are infected with mosquito-borne viruses do not become ill and have no symptoms. For persons who do become ill, the time between the mosquito bite and the onset of symptoms, known as the incubation period, ranges from 5-15 days.

Two clinically different types of disease occur in humans:
  • Encephalitis: An inflammation of the brain.
  • Viral fever syndrome: Symptoms of the viral fever syndrome include fever, headache, and malaise. These symptoms persist for about 2-7 days.

Prevention & Control
To decrease exposure to mosquitoes and the viruses they may carry:
  • Limit outside activity around dawn and dusk. This is particularly important for elderly adults and small children.
  • Wear protective clothing such as lightweight long pants and long sleeve shirts when outside.
  • Apply insect repellant to exposed skin when outside. Products with 10% or less of DEET are recommended for children.
  • Make sure that doors and windows have tight fitting screens. Repair or replace screens that have tears or holes in them.
  • Drain all standing water on private property, no matter how small an amount.
  • Stock permanent ponds or fountains with fish that eat mosquito larvae. Change water in birdbaths or wading pools and empty flowerpot saucers of standing water at least once a week.
  • Check around faucets and air conditioner units and repair leaks or puddles that remain for several days.
  • Make sure roof gutters drain properly and remove any standing water under, around structures, or on flat roofs.
  • Remove items that could collect water such as old tires, buckets, empty cans, and food and beverage containers.
  • Eliminate seepage and standing water from cisterns, cesspools, septic tanks, and animal watering tanks.
  • Do not over-water lawns and gardens to prevent standing water.

Contact Information
For additional information, visit Colorado Department of Public Health and Environment's website or contact Grand County Public Health at 970-725-3288.