West Nile Virus

What is West Nile Virus?
It is a potential serious illness that is commonly carried by infected mosquitoes. West Nile Virus is established as a seasonal outbreak in North America that flares up in the summer and continues into the fall.

Where does it occur?
West Nile Virus was not introduced into the Western Hemisphere until the 1999 outbreak in New York City. Since then, the disease has spread across the United States (http://diseasemaps.usgs.gov/wnv_us_human.html for map.) It also occurs in Africa, West Asia, and the Middle East.

How is it spread?

  • Most often, it is spread by the bite of an infected mosquito. Mosquitoes become infected after feeding on infected birds. The mosquito can spread the virus to humans and other animals when they bite.
  • In a small number of cases it has been spread through blood transfusions, organ transplants, breast feeding, and even during pregnancy from mother to baby.
  • West Nile Virus is not spread through casual contact such as touching or kissing a person with the virus.

For pictures of modes of transmission: http://www.cdc.gov/ncidod/dvbid/westnile/birds&mammals.htm

Signs and Symptoms:
Approximately 80% of people who are infected will not show any symptoms at all. People typically develop symptoms between 3 to 14 days after they have been bitten by the infected mosquito. Symptoms can last for as short as a few days or up to several weeks.

Mild signs and symptoms:

  • Fever
  • Headache
  • Body aches
  • Nausea
  • Vomiting
  • Skin rash on the chest, stomach, and back

Serious signs and symptoms:

  • High Fever
  • Headache
  • Neck stiffness
  • Tremors (involuntary trembling or shaking)
  • Convulsions (abnormal involuntary contraction or series of contractions of the muscles)
  • Vision loss
  • Numbness and loss of feeling

These symptoms may last several weeks. Neurological effects could be permanent.


There is no specific treatment for West Nile Virus.

  • Treatment of severe illnesses includes:
    • Hospitalization
    • Intravenous (IV) fluids
    • Nutrition
    • Respiratory support
    • Prevention of secondary infections
    • Good nursing care

There is no vaccine to prevent West Nile Virus. The best way to avoid contracting West Nile Virus is to prevent and avoid mosquito bites.

  • Apply insect repellent containing DEET to exposed skin. Do not spray repellent on skin that will be under clothing. Do not use permethrin on skin.
  • Wear long sleeves, long pants, and socks when outdoors.
  • Drain standing water. Small amounts of water can be a good place for mosquitoes to lay their eggs.
  • Limit time outdoors between dusk and dawn. This is when mosquitoes tend to bite because this is their feeding time.
  • Fix or install window and door screens to keep mosquitoes from entering the home.

For additional information on how to prevent mosquito bites:

For further information on West Nile Virus:

For additional information about insect repellents:

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