West Nile Virus
Alternate Names : Flavivirus, West Nile Encephalitis, West Nile Meningitis
This virus belongs to a group of disease-causing viruses known as flaviviruses.
Other viruses in this group include yellow fever virus, St. Louis encephalitis virus, and dengue virus.
The infection caused by West Nile virus is one of the newest infectious diseases in the US, having
been diagnosed for the first time in 1999 in New York City. It has been common in the eastern part
of the world for many years, especially in Africa, Europe, and the Middle East.
What is going on in the body?
West Nile virus is spread between mosquitoes and certain infected birds, such as
crows. Once a mosquito bites an infected bird, it can then transfer the virus to a human that it bites
later. Most people do not develop enough virus in the bloodstream to become sick. For those who do,
they usually become ill within 3 to 15 days after they are bitten. Most people who do get sick have
only mild symptoms, but in a few people, the virus crosses from the blood into the brain. This results
in more serious symptoms that may even cause death. In these cases, the virus causes an
inflammation of the brain known as West Nile encephalitis.
What are the causes and risks of the infection?
Anyone who is bitten by a mosquito infected with the West Nile virus may develop
symptoms, but only about 1 in 5 people actually do. And most of those people only
have very mild symptoms. Experts know that the
risk of being bitten by an infected mosquito is linked to living in an area where West Nile virus has
spread, and to spending time outdoors where infected mosquitoes can be found.
About 1 in 150 people bitten by a West Nile-infected mosquito will develop
encephalitis. Age is the greatest risk factor for severe neurologic disease, for long-term illness,
and for death. In fact, people who are ages 50 to 59 have 10 times the risk of younger
people for developing serious disease. Those
who are age 80 or older are 43 times as likely to develop serious illness. People age 75 and older are
9 times more likely to die as a result of West Nile encephalitis.
NOTE: Anyone with severe or unusual headaches should seek medical
attention right away.