West Nile enecephalitis is an infection of the brain caused by the West Nile virus,a flavirius, commonly found in Africa, Eastern Europe, and Western Asia. It is closely related to St.Louis encephalitis virus found in the United States. Untill 1999, West Nile virus had not been documented in the western hemisphere. The West Nile virus found in the United States is more closely related genetically to straina. The West Nile virus is more commonly found in the middle east.

Mosquitos spread the virus through a mosquito-bird cycle. This cycle is started when a mosquito extracts blood from an infected bird and becomes a carrier of the virus. When this carrier mosquito then extracts blood from a non-infected bird, the virus is transmitted to the bird. If another mosquito then extracts blood from the infected bird, the second mosquito then becomes the carrier of the virus. In a similar manner, if a carrier mosquito extracts blood from a human or an animal, the virus is transmitted to the human or the animal. There are no known cases where the viru

The West Nile virus has no specific therapy. In some cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, and respiratory support (ventilator) to prevent secondary infection.

All residents in areas where virus activity has deen identified are at risk of getting West Nile virus. Persons older than 50 years have the highest risk of severe disease. Most infections are mild, and symptoms include fever, headache, and body aches, occasionally with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death. The incubatuion period in humans (time from infection to the onset of disease symptoms) for West Nile virus is three to fifteen days. People who think they have West Nile virus should contact their health care prvider if they develop symptoms such as high fever, confusion, muscle weakness, and severe headaches.

The American crow is one of the bird species affected by the West Nile virus. Surveillances of dead crows has been used to monitor the spread of the virus. The crow is a partially migratory species. In the summer it can be found from the south eastern United States to nothern Canada. In the fall it migrates from Canada to the United States and extends its habitat to include most of the United States. Some of the crows in the New York area migrate to the south while others remain in the New York area. This is what is meant by partially migratory.

How the West Nile virus spread to the Unite

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