History & Symptoms of West Nile Virus

The West Nile Virus (WNV) is a mosquito-borne virus that is commonly found in Africa, West Asia, and the Middle East, and in recent years has been found in the United States. Symptoms become noticeable 3 to 14 days after being bitten by an infected mosquito.

Most people infected with the WNV experience few if any symptoms and recover completely after a few days. Mild symptoms include a fever, headache, body aches, occasionally with a skin rash on the trunk of the body, and swollen lymph glands. Although rare, some people experience severe infection (West Nile encephalitis or meningitis) and the symptoms include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.

Persons over about 55 or with preexisting health conditions are more likely to develop severe illness. Symptoms of severe disease may last several weeks, although neurological effects may be permanent.

Mosquitoes become infected with the WNV when they feed on infected birds and can then transmit the virus to humans and animals while biting to take blood. WNV cannot be transmitted from person-to-person. Other possible transmission routes of the virus are being studied. In areas where the virus is circulating, very few mosquitoes are infected. Even if the mosquito is infected there is a very low chance that people who get bitten and become infected will get severely ill. The chances you will become severely ill from one mosquito bite are extremely small.