Introduction | What It Is and How It's Transmitted | Prevention | Humans and West Nile | Animals and West Nile | Research and Surveillance | Resources About West Nile Virus
As the name suggests, West Nile virus was first found in the West Nile District of Uganda in 1937. It occurred in Africa, West Central Asia, the Middle East, and Europe before it appeared in the eastern United States in 1999.
West Nile virus is one of a group of disease-causing viruses known as flaviviruses, which are spread by arthropods, usually mosquitoes and ticks. Other flaviviruses include those that cause yellow fever, dengue, and St. Louis encephalitis.
Courtesy of Centers for Disease Control and Prevention.
In the United States, West Nile virus has been found in 43 species of mosquitoes, but mosquitoes in the genus Culex are thought to be the primary transmitters.
Mosquitoes pick up West Nile virus when they feed on a bird that carries it. So far, West Nile virus has been found in more than 170 bird species, ranging from bluebirds to warblers.
Although the virus primarily circulates between birds and mosquitoes, mosquitoes can transmit the infection to other animals and humans.
Courtesy of Pennsylvania State University.
But even in areas with high numbers of infected birds, not all mosquitoes are infected, and not all people bitten by mosquitoes develop illness. A 1999 study of New York City residents in Queens showed that only 2.6 percent had been infected. Only 62 people had developed overt clinical illness.
Humans may get sick from West Nile virus, but it is thought that they do not usually develop enough virus in their bloodstream to infect mosquitoes. Nor can the virus be casually spread from person to person.
West Nile virus can, however, be transmitted through blood transfusions and organ donations. One case suggests that infection can be transmitted through breast feeding.
To prevent transmission during medical procedures, the U.S. Food and Drug Administration (FDA) has issued guidelines to blood banks to help blood centers determine which potential donors should be excluded from giving blood. A new test to detect West Nile virus went into use by U.S. blood banks in July 2003.
FDA has also cleared a test that will be used in the diagnosis of West Nile virus Infection in people.
Currently the only way to control the spread of West Nile virus is to control the mosquitoes that carry the virus and avoid being bitten.
Introduction | What It Is and How It's Transmitted | Prevention | Humans and West Nile | Animals and West Nile | Research and Surveillance | Resources About West Nile Virus
Oct. 8, 2003
|
 
|
