|
West
Nile Virus: Q & A
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. Historically, where
has West Nile encephalitis occurred worldwide?
A. See the map describing distribution of flaviviruses, including West Nile
virus:
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. 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 mosquitoes found to carry West Nile virus is the Culex
species, which survives through the winter, or "overwinters," in the
adult stage. That the virus survived along with the mosquitoes was documented by
the widespread transmission during the summer of 2000.
Q. Is West Nile virus
now 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.
|
