Most people infected with West Nile virus have no symptoms. About 20 percent develop symptoms that include fever, fatigue, headache and muscle or joint pains. These symptoms can last a few days to several weeks. Less than 1 percent of infected people will develop a more serious illness with symptoms that include headache, high fever, stiff neck, disorientation, convulsions, tremors and muscle weakness. Severe cases of the virus may lead to paralysis, coma or death.
Symptoms typically appear three to 15 days after the mosquito bite. People age 50 and older are more likely to develop severe symptoms from West Nile virus.