 |
 |
|
|||||||||
|
|||||||||
| ||||
WNV is our most recent experience with emerging mosquito-borne disease. While new to the United States, it is not an emergent disease outside the Western Hemisphere. The virus was initially isolated from the blood of a woman in the West Nile District of Uganda in 1937, and subsequently found in humans, birds, and mosquitoes during studies conducted in Egypt throughout the 1950s. WNV is closely related to others in the genus Flavivirus and family Flaviviridae responsible for Japanese encephalitis, Murray Valley encephalitis and St. Louis encephalitis. Birds are the natural reservoir host and serve in the amplification of the virus. WNV is maintained in a mosquito-bird-mosquito epizootic transmission cycle, while humans (and other mammals) are incidental, dead-end hosts. WNV is now recognized as the most widespread of all the flaviviruses and has been isolated in more than 40 species of mosquitoes in at least 30 countries across Africa, Asia, Europe, and North America. Since its discovery in 1999, WNV, an exotic species, has firmly established itself in the continental United States: 44 states and the District of Columbia report evidence of the virus. However, mosquito-borne diseases are not new to the United States. There are records of malaria and yellow fever epidemics as early as the 1690's, and the period between 1793 and 1806 is referred to as the "yellow fever era" in America. Through persistent public health intervention neither disease is presently endemic in the United States. Prior to WNV, the last major outbreak of a mosquito-borne disease in the United States occurred in the Midwest during 1975, with more than 2,000 documented cases of St. Louis encephalitis and 142 deaths. West Nile virus (WNV) poses a threat to wildlife species as well. Although humans, horses, and other animals can become ill from WNV, birds are the natural host for the virus. High avian mortality, not observed in WNV outbreaks in the eastern hemisphere, is being observed in the United States and Canada. Highest mortality has been observed in birds in the corvid family (crows, jays, and related species). Some raptor species also appear highly susceptible to WNV. Thus far, WNV has been detected in over 160 bird and 15 mammal species, as well as captive alligators. Some reports estimate the number of birds that potentially died of WNV at well over a million. Monitoring bird populations and dead bird surveillance are important wildlife management activities that can be performed by NPS staff. Parks also offer excellent opportunities for use as outdoor laboratories for cooperative research on WNV. Prevention and Control of West Nile Virus Mosquito-borne diseases can be prevented in two major ways: personal protective measures to reduce contact with mosquitoes and public health measures to reduce the population of infected mosquitoes in the environment. Personal protection measures include:
Repellents may be applied directly to the skin or to clothing, window screens, mesh insect nets, tents, or sleeping bags. Persons who are particularly concerned about potential toxicity from DEET may limit application of the repellent to their clothes. Repellents containing DEET can damage plastics (such as watch crystals and eyeglasses frames), rayon, spandex, other synthetic fabrics, leather, and painted or varnished surfaces. DEET does not damage natural fibers, such as cotton or wool, and has no effect on nylon. For detailed information mosquito repellents and insecticides, the following references are provided: EPA Office of Pesticide Programs National Pesticide Information
Center Public health prevention and control strategies for of West Nile virus are most effectively accomplished through integrated vector management programs. These programs include surveillance for West Nile virus activity in mosquito vectors, birds, horses, other animals, and humans, and implementation of appropriate mosquito control measures to reduce mosquito populations (e.g., elimination of larval habitats or spraying of insecticides to kill juvenile (larvae) and adult mosquitoes) when necessary. Additionally, when virus activity is detected in an area, residents are alerted and advised to increase measures to reduce contact with mosquitoes. The following are practical risk reduction strategies that can be used around the home and the workplace:
Additional Resources For area-specific information, contact your state or local health department. The Centers for Disease Control and
Prevention has established a hotline for questions about West Nile Virus.
The tollfree phone line provides the latest information on West Nile Virus.
The CDC West Nile Virus Hotline is: |
||||
|
| ||||
