Most people infected with West Nile virus will not have any signs of illness. Twenty percent of people who become infected will have mild symptoms such as fever, headache, body aches, and occasionally a skin rash on the trunk of the body and swollen lymph glands.
The symptoms of severe infection (West Nile neuroinvasive disease) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Only about one out of 150 people infected with West Nile virus will develop this more severe form of the disease.
The incubation period of West Nile virus in humans is three to 14 days. Symptoms of mild disease may last a few days. Symptoms of severe disease may last several weeks, although neurological effects may be permanent. Rarely, death can occur.