What is West Nile Virus
West Nile Virus is a flavivirus which is carried by mosquitoes. It is transmitted when a mosquito bites an infected bird, and then bites another animal or human.
West Nile virus, West Nile fever, and West Nile encephalitis are different terms describing the same virus but refers to different medical states. Originally found in Africa, West Asia and the Middle East, West Nile virus was first confirmed in the United States in 1999 and in Kansas in 2002.
West Nile Fever is characterized by flu-like symptoms which last just a few days. Symptoms normally show up 3-15 days after the mosquito bite.
A more severe case of 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.
Very rarely, acute West Nile Virus infection has been associated with acute flaccid paralysis (AFP). AFP presents as a polio-like syndrome without pain or loss of sensation. Patients do not usually have meningitis or encephalitis if AFP is present.
The exact cause of AFP in West Nile Virus has not been thoroughly determined, although anterior horn cell involvement with a resultant poliomyelitis-like syndrome is most likely. Risk factors for developing AFP are not well known, but are being studied. AFP from West Nile Virus must be differentiated from Guillain-Barre syndrome (which can also cause weakness and sensory loss) because treatments for Guillain-Barre are not effective for West Nile Virus and may be detrimental to persons with West Nile Virus. For more information see: http://wwwnc.cdc.gov/eid/article/9/7/03-0129_article .
Less than 1% of people infected by West Nile Virus develop serious illness. Most people infected have no symptoms at all.