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Health Department

Mosquitoes and West Nile Virus

West Nile virus is transmitted to humans through the bite of an infected mosquito. Although most people (8 in 10) who are infected do not feel sick, about 1 in 150 develop a serious, sometimes fatal, illness. People over age 60 are at greater risk for severe illness. Learn more about West Nile virus in the drop-downs below.

Click to learn more about West Nile Virus.

What is West Nile virus?

West Nile is a virus most commonly spread by infected mosquitoes. People can’t give West Nile virus to other people. The risk to humans occurs primarily from June through early September, when mosquitoes are active.

How do people get infected with West Nile virus?

Most people get West Nile virus from the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans, birds, and other animals such as horses.

Who is at risk for infection with West Nile virus?

Anyone living in an area where West Nile virus is present in mosquitoes can get infected. Colorado has had cases of West Nile virus every year since 2002. The risk of infection is highest for people who work outside or participate in outdoor activities, because of greater exposure to mosquitoes.

People of any age can get West Nile virus. However, people older than 60 years are at the greatest risk for severe disease. People with certain medical conditions such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants are also at greater risk for serious illness.

What are the symptoms of West Nile virus?

Most people infected with West Nile virus don’t get sick. For people who do, the time between the mosquito bite and the start of symptoms can be from two to 14 days. In rare cases, the virus can cause a serious brain infection such as meningitis or encephalitis. These infections begin suddenly with high fever and headache and may progress to stiff neck, disorientation, tremors, and coma. Severe infections can result in permanent brain damage or death. Most
deaths occur in people older than 50 years.

There is no treatment for West Nile virus infection, but milder West Nile Virus illness usually improves on its own. Prevention is key, especially for older adults and people with immunosuppressing medical conditions at higher risk of severe illness. Rest, fluids, and over-the-counter pain medications may relieve some
symptoms. If you think you or a loved one is sick with West Nile virus, talk with a health care provider.

How can people protect themselves from West Nile virus?

The most effective way to prevent West Nile virus disease is to prevent mosquito bites.

To protect yourself:

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus, as well as para-menthane-diol products provide the best protection. For more information about insect repellents visit the EPA’s information webpage. Follow label
  • Limit outdoor activities at dusk and dawn, when mosquitoes that carry West Nile virus are most active.
  • Wear protective clothing (long pants, long-sleeved shirts, and socks) in areas where mosquitoes are active. Spray clothes with insect repellent for extra

To mosquito-proof your home:

  • Drain standing water around your house at least once a week. Empty water from tires, cans, flowerpots, clogged gutters, rain barrels, birdbaths, toys, and puddles.
  • Install or repair screens on windows and doors.