Home About Us Services Library Where We Are Contact Us
FOH Articles External Resources FOH Fact Sheets

West Nile Virus Fact Sheet
“Human illness from West Nile virus (WNV) is rare, even in areas where the virus has been reported. The chance that any one person is going to become ill from a mosquito bite is low.”
Centers for Disease Control and Prevention (

Where is West Nile Virus Found?

  • West Nile virus is currently found in many areas of the eastern half of the United States.
  • The most recent reported human infections have been in Louisiana, Mississippi and Texas.
  • West Nile Virus in the United States link from CDC
How is WNV Transmitted?
  • WNV is transmitted to humans through mosquito bites. Mosquitoes become infected when they feed on infected birds that have high levels of WNV in their blood. The virus is spread by the bite of an infected mosquito, and can infect people, horses, many types of birds, and some other animals.
  • WNV is not transmitted from person to person and there is no evidence that handling live or dead infected birds can infect a person. But, to add a further level of safety, if birds or other potentially infected animals must be handled, a protective barrier (e.g., gloves, inverted plastic bags) should be used.
  • The risk of severe disease is higher for persons 50 years of age and older.
Prevention of WNV
  • Avoid Mosquito Bites to Avoid Infection
  • To avoid mosquito bites, you can limit the number of places available for mosquitoes to lay their eggs by eliminating standing water sources from around your home.
  • Stay indoors at dawn, dusk, and in the early evening.
  • Wear long-sleeved shirts and long pants whenever you are outdoors.
  • Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.
  • Apply insect repellent sparingly to exposed skin. An effective repellent will contain 35% DEET (N,N-diethyl-meta-toluamide). DEET in high concentrations (greater than 35%) provides no additional protection.
  • Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children.
  • Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE, as printed on the product.
  • Install or repair window and door screens so that mosquitoes cannot get indoors.
  • Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.
Symptoms of WNV
  • Most WNV infected humans have no symptoms.
  • A small proportion develops mild symptoms that include fever, headache, body aches, skin rash and swollen lymph glands.
  • Less than 1% of infected people develop more severe illness that includes meningitis (inflammation of the spinal cord) or encephalitis. The symptoms of these illnesses can include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Of the few people that develop encephalitis, a small proportion die but, overall, this is estimated to occur in less than 1 out of 1000 infections.
Treatment for WNV
  • There is no specific treatment for WNV infection or vaccine to prevent it.
  • Treatment of severe illnesses includes hospitalization, use of intravenous fluids and nutrition, respiratory support, prevention of secondary infections, and good nursing care. Medical care should be sought as soon as possible for persons who have symptoms suggesting severe illness.
Reporting dead birds
  • Dead birds in an area may mean that West Nile virus is circulating between the birds and the mosquitoes in that area. Over 110 species of birds are known to have been infected with West Nile virus. Although birds, particularly crows and jays, infected with WN virus can die or become ill, most infected birds do survive.
  • The public can play an important role in monitoring West Nile virus through reporting dead birds to state and local health departments. States have different policies for collecting and testing bird, so see the Links to State and Local Government Sites page to find out how to report dead birds in your area.
Do you have other questions about West Nile virus? See...

Questions and Answers
Answers to the most common questions

CDC West Nile Virus Home Page
General and technical information on the subject

West Nile virus transmission cycle
Learn about the birds and mammals affected by West Nile virus.

Links to State and Local Government Sites
Links to local information about West Nile virus

CDC public inquiry hotline: The English number is 1-888-246-2675. The Spanish hotline is 1-888-246-2857, and the hotline for the hearing-impaired is 1-866-874-2646.

Source for all information contained in this fact sheet:
Centers for Disease Control and Prevention (
Division of Vector-Borne Infectious Diseases (

Improving the health, safety, and productivity of our Federal employees.
Privacy Policy | Rules of Behavior | Terms of Use | Accessibility | FOIA | Disclaimers | The White House |