West Nile Virus Brochure
Frequently Asked Questions (FAQ)
What is West Nile Virus?
West Nile virus can be a serious, even fatal, illness. It can affect people, horses, certain types of birds, and other animals. In 1999, West Nile virus first appeared in the United States in New York City. Since that time, it has spread rapidly throughout the country, and into parts of Canada, Mexico, Central America, and South America. To date, October 2007, there has been no West Nile virus detected in Hawaii.
For an overview of West Nile virus, visit the Centers for Disease Control and Prevention.
How is it spread?
Infected Mosquitoes. West Nile virus is almost always spread to people by the bite of an infected mosquito. Mosquitoes become infected after feeding on birds that carry the virus. There is no evidence that West Nile virus can be spread by direct contact with infected people or animals.
Transfusions, Transplants, and Mother-to-Child. In a very small number of cases, WNV also has been spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.
Not through touching. WNV is not spread through casual contact such as touching or kissing a person with the virus.
As we learn more about West Nile virus, other routes of infection are being discovered. For more information, visit the Centers for Disease Control and Prevention.
Who is at risk?
The risk of getting West Nile virus is very low, but anyone can become infected. People over 50 years of age have the highest risk of serious illness.
How soon do infected people get sick?
People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.
What are the symptoms in people?
Most people who are infected with West Nile virus will not feel ill at all! About 1 in 5 people infected will have mild symptoms such as fever, headache, and body aches. Even fewer, about 1 in 150 people infected, will have more severe symptoms. Severe symptoms may include headache, high fever, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, paralysis, and coma. If you have any of these symptoms, contact your health care provider immediately.
How Is WNV infection treated?
There is no specific treatment for WNV infection. In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.
Are wild mammals or pets at risk?
Mammals in general are very resistant to infection with West Nile virus. Although individual wild mammals may be bitten by infected mosquitoes, they generally produce an immune response that prevents infection. Thus, if we take a blood sample, we can find antibodies in various mammals, but there is no virus present that could be passed on to mosquitoes. Of course, as with any infective agent, some individuals may not develop immunity and could become sick or perhaps even die. The West nile virus has been detected in 35 mammal species including domestic cattle, reindeer, harbor seal, little brown bat, rhesus macaque, Asian elephant and gray squirrel. The virus has also been identified in two reptile species, American alligators and crocodile monitors.
West Nile virus has been isolated from cats that were ill and died, however dogs and cats rarely develop clinical illness from WNV infection. Fewer than 40 dogs and one cat were reported to be infected with WNV in 2003. In a study of dogs tested in Queens, New York in 1999, 5 to 11% of dogs had serological evidence of exposure to WNV, but did not have clinical disease. Experimentally infected dogs showed no clinical signs of WNV, however some cats had mild clinical signs of illness including fever and lethargy.
Horses are an exception to the general rule for mammals and they are more susceptible to West Nile virus and closely related viruses. Veterinarians and horse owners, with ill horses showing symptoms compatible with West Nile virus, should have them tested for West Nile virus. Fortunately, there is an effective West Nile virus vaccine for horses. For more information about horses see the Equine Surveillance section of this web page.
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