West Nile Virus Information

Q. How do people get infected with West Nile virus (WNV)?
A. The principal route of human infection with West Nile virus is through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus eventually finds its way into the mosquito's salivary glands. During subsequent blood meals, the virus may be injected into humans and animals, where it can multiply and possibly cause illness.

Additional routes of infection have become apparent during the 2002 West Nile epidemic. It is important to note that these other methods of transmission represent a very small proportion of cases. A recent investigation has confirmed WNV transmission through transplanted organs. Investigations of other patients who developed WNV infection within several weeks of receiving blood products or organs are ongoing to determine whether WNV was transmitted by transfusion or transplantation in any of these cases.

There is one reported case of transplacental (mother-to-child) WNV transmission. Although transmission of WNV and similar viruses to laboratory workers is not a new phenomenon, two recent cases of WNV infection of laboratory workers have been reported.

Q: What are West Nile virus, West Nile fever, and West Nile encephalitis?
A. West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus found in the United States. The virus can infect humans, birds, mosquitoes, horses and some other mammals.

West Nile fever is a case of mild disease in people, characterized by flu-like symptoms. West Nile fever typically lasts only a few days and does not appear to cause any long-term health effects.

More severe disease due to a person being infected with this virus can be West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it.

Q. Where did West Nile virus come from?
A. West Nile virus has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. It is not known from where the U.S. virus originated, but it is most closely related genetically to strains found in the Middle East.

Q. How long has West Nile virus been in the U.S.?
A. It is not known how long it has been in the U.S., but CDC scientists believe the virus has probably been in the eastern U.S. since the early summer of 1999, possibly longer.

What is the County Vector Control Program doing to address the problem of West Nile virus?
A. The San Bernardino County Vector Control Program, along with the California Department of Health Services and the Centers for Disease Control and Prevention, has developed a comprehensive monitoring and surveillance plan to detect West Nile virus in the county and limit the residents' risk of exposure to the infection. Vector Control Program routinely tests for West Nile Virus in sentinel chicken flocks maintained at various sites in the county and mosquito populations collected throughout the county. Sick, dying or dead birds that meet certain collection guidelines are also tested for West Nile virus.

(Information on this page obtained from the Centers for Disease Control and Prevention)

For West Nile Virus information updates call toll free:
877-WNV-BIRD (877-968-2473)
Web site: http://www.westnile.ca.gov

For West Nile Virus information from the Centers for Disease Control:
Visit web site: http://www.cdc.gov/ncidod/dvbid/westnile

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