Most people who are infected with the West Nile virus (WNV) will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever with mild symptoms, including fever, headache, and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands. Incubation is usually 3 to 15 days.
It is estimated that 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. The symptoms of severe infection (West Nile encephalitis or meningitis) include:
- High fever
- Muscle weakness
- Neck stiffness
All residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis; persons over 50 years of age have the highest risk of severe disease. It is unknown if immuno-compromised persons are at increased risk for WNV disease.