West Nile Virus -  Fact Sheet


What is West Nile virus?

West Nile virus is spread by mosquitoes and can cause illness in people and animals. It is named after the West Nile district of Uganda where the virus was first isolated in 1937. West Nile virus and St. Louis Encephalitis virus come from the same family of viruses, called flaviviruses, and cause diseases that are similar to one another.

Have there been any human cases of West Nile virus infections in Connecticut?

West Nile virus was found in the United States for the first time in 1999. Since then 134 state residents have become ill due to infection with the virus including 128 persons infected in Connecticut and 6 who were infected while traveling in other states. Three persons have died.

How do people get West Nile virus?

West Nile virus, like St. Louis Encephalitis virus, is spread to humans by the bite of infected mosquitoes (primarily the Culex species). A mosquito is infected by biting a bird that carries the virus. In rare instances, the virus has been spread by blood transfusion, organ transplant, breastfeeding, and from mother to child during pregnancy.

What are the symptoms of West Nile virus infection?

Most people who are infected have no symptoms or may experience mild illness before fully recovering. In some individuals, particularly the elderly, West Nile virus can cause serious disease that affects the nervous system. At its most serious, it can cause damage to the body’s nervous system. Symptoms generally occur 3-14 days following the bite of an infected mosquito, and range from fever, headache, body aches, nausea, and less frequently skin rash and swollen nodes to severe headache, high fever, stiff neck, disorientation, muscle weakness, coma, or death.

Who is at risk of West Nile virus infection?

Anyone can become infected with the virus, however, people over 50 years are more likely to become ill and develop serious symptoms when infected. Outdoor activities is the principal risk factor. The risk from medical procedures is very low – donated blood is tested. Pregnancy and nursing also present a very low risk.

If I live in an area where mosquitoes with West Nile virus have been reported and I am bitten by a mosquito, am I likely to get sick?

No. Even in areas where mosquitoes do carry the virus, very few mosquitoes (usually less than 1 in 500) are infected. The chance that one mosquito bite will be from an infected mosquito is extremely small. If bitten by an infected mosquito, chances of developing illness are roughly one in 300.

If bitten by a mosquito, should I be tested for West Nile virus?

No. Most mosquitoes are not infected with the West Nile virus. However, you should see a doctor immediately if you develop symptoms such as high fever, confusion, muscle weakness, or severe headaches. Patients with mild symptoms are likely to recover completely, and do not require any specific medication or laboratory testing.

Is there a treatment for West Nile virus infection?

Although there is no specific treatment, medication or cure, the symptoms and complications of the disease can be treated. Most people who get this illness recover from it.

Is there a vaccine for West Nile virus?

No vaccine for West Nile fever is currently available.

How can I reduce mosquitoes around my home?

Mosquitoes require water for reproduction. The following are measures that can help reduce mosquitoes:

  • Elimination of standing water suitable for mosquitoes
  • Dispose of water-holding containers, such as ceramic pots, used tires, and tire swings.
  • Drill holes in the bottom of containers such as those used for recycling.
  • Clean clogged roof gutters.
  • Turn over objects that may trap water when not in use, such as wading pools and wheelbarrows.
  • Change water in bird baths on a weekly basis.
  • Clean and chlorinate swimming pools. When pools are not in use, use pool covers and drain when necessary.

How can I avoid mosquito bites when outdoors?

Mosquitoes require a blood meal for reproduction. The following are measures that can help reduce bites from mosquitoes that feed on people:

  • Be particularly careful at dusk and dawn when mosquitoes are most active.
  • Wear shoes, socks, long pants, and long-sleeved shirts. Clothing material should be tightly woven.
  • Use mosquito netting when sleeping outdoors.
  • Consider using mosquito repellent when it is necessary to be outdoors. Always use according to label instructions. The most effective repellents contain DEET or Picaridin.
  • When using DEET, use the lowest concentration effective for the time spent outdoors (for example, 6% lasts approximately two hours and 20% for four hours) and wash treated skin when returning indoors.  Do not apply under clothing, to wounds or irritated skin, the hands of children, or to infants less than two months old.
  • Also, be sure door and window screens are tight fitting and in good repair to avoid mosquito bites when indoors.

What should I do if I find a dead bird?

Dead birds can be placed in a double plastic bag and placed out with the household trash or brought to a municipal landfill. Birds can also be disposed of on-site by burying. Disposal is subject to municipal restrictions so call your town hall. As for all dead animals, avoid handling birds with bare hands. A plastic bag can be placed over your hands before grasping the bird and then the edges pulled over it.

This fact sheet is for informational purposes only. It should not be used for self-diagnosis or as a substitute for consultation with a health care provider. If you think that you may have this infection, or have questions about the disease described above, you should consult your health care provider.

For additional information on this disease, visit the Centers or Disease Control and Prevention website.

To contact the Epidemiology and Emerging Infections Program, please call 860-509-7994.