West Nile Virus

Infectious agent: :  West Nile Virus, member of the family Flaviviridae, genus Flavivirus.

Description of illness: West Nile virus (WNV) is a mosquito-borne virus that can cause febrile illness, encephalitis or meningitis. The incubation period is usually 2 to 6 days. Most people who become infected with WNV will not experience any illness. About 1 in 5 will develop a fever, along with headache, body aches, joint pains, vomiting, diarrhea or rash. Most people recover completely. However, less than 1% will develop encephalitis or meningitis, with headache, fever, neck stiffness, disorientation, coma, tremors, seizures or paralysis. Recovery may take several weeks or months, and some neurologic effects may be permanent. About 1 in 10 individuals with West Nile encephalitis will die. Persons over 60 years of age are at the greatest risk for severe disease, as well as those with underlying medical conditions. No specific treatment or vaccine exists.