of West Nile Virus
What is West Nile virus?
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 which is also found in the United States.
The virus can infect humans, birds, mosquitoes, horses and some
What are West Nile encephalitis, West Nile meningitis and “neuroinvasive
disease” and West Nile fever?
A. The most severe type of disease due to a person
being infected with West Nile virus is sometimes called “neuroinvasive
disease” because it affects a person’s nervous system.
Specific types of neuroinvasive disease include: 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
West Nile Fever is another type of illness that can occur in
people who become infected with the virus. It is characterized
by fever, headache, tiredness, aches and sometimes rash. Although
the illness can be as short as a few days, even healthy people
have been sick for several weeks.
Historically, where has West Nile encephalitis occurred worldwide?
A. See the map describing distribution of flaviviruses, including
West Nile virus:
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.
I understand West Nile virus was found in "overwintering"
mosquitoes in the New York City area in early 2000. What does
A. One of the species of mosquitoes 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.
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
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.