West Nile virus is a potentially serious illness. Experts believe it is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. About one in 150 people infected with West Nile virus will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent. Up to 20% of the people who become infected have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks. Approximately 80% of people who are infected with West Nile virus will not show any symptoms at all.