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Overview of West Nile Virus
West Nile
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Reporting Dead Birds
Q. What is West
Nile encephalitis?
A. "Encephalitis" means an inflammation of the
brain and can be caused by viruses and bacteria, including viruses
transmitted by mosquitoes. West Nile encephalitis is an infection of the
brain caused by West Nile virus, 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.
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.
Historically, where has West Nile encephalitis occurred
worldwide?
A. See the map describing distribution of flaviviruses,
including West Nile virus: View enlarged
image.
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.
Q. How many cases
of West Nile encephalitis in humans have occurred in the U.S.?
A.
In 1999, 62 cases of severe disease, including 7 deaths, occurred in the
New York area. In 2000, 21 cases were reported, including 2 deaths in the
New York City area. In 2001, there were 66 human cases of severe
disease and 9 deaths. No reliable estimates are available for the number
of cases of West Nile encephalitis that occur worldwide.
Please see CDC's current case count
for information on 2002 cases in the U.S..
Q. I understand
West Nile virus was found in "overwintering" mosquitoes in the New York
City area in early 2000. What does this mean?
A. One of the species
of mosquitos found to carry West Nile virus is the Culex species
which survive through the winter, or "overwinter," in the adult stage.
That the virus survived along with the mosquitoes was documented by the
widespread transmission the summer of 2000.
Q. Do the findings
indicate that West Nile virus is established in the Western
Hemisphere?
A. The continued expansion of West Nile virus in the
United States indicates that it is permanently established in the Western
Hemisphere.
Q. Is the disease
seasonal in its occurrence?
A. In the temperate zone of the world
(i.e., between latitudes 23.5° and 66.5° north and south), West Nile
encephalitis cases occur primarily in the late summer or early fall. In
the southern climates where temperatures are milder, West Nile virus can
be transmitted year round.
Please see the links below for the complete FAQ on West Nile
Virus from the CDC's Website
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| Please see
CDC.gov
website for more
Posted
08/27/02
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