West Nile virus and your health

What is West Nile virus?
  • West Nile is a virus most commonly spread by infected mosquitoes. 
  • Person-to-person transmission does not occur. Risk to humans occurs primarily from July through early September when mosquitoes are active.

How do people get infected with West Nile virus?

  • Most people get infected with West Nile virus by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other birds. 
  • In a very small number of cases, West Nile virus has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy or at the time of birth. 

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 over 60 years of age 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 mosquito-borne viruses do not become ill. For people who do, the time between the mosquito bite and the start of symptoms can be from 5 to 15 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 a 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 persons over 50 years of age. There is no treatment for the virus other than supportive care, and there is no vaccine to prevent it. If you think you or a family member is sick with West Nile virus, consult a health care provider. 
How can people prevent getting West Nile virus?
The most effective way to prevent West Nile virus disease is to prevent mosquito bites:
  • Use insect repellents when you go outdoors.  Choose an EPA-registered product, and follow the label directions carefully.
  • Wear long sleeves and pants from dusk through dawn when the mosquitoes that carry West Nile virus are most active.
  • Install or repair screens on windows and doors. If you have air conditioning, use it.
  • Empty standing water from containers such as flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires and birdbaths so mosquitoes can’t grow in them.