West Nile virus is a disease that is spread by the bite of a mosquito infected with the virus. Most people who are infected with West Nile virus do not develop any symptoms. However, about 20% of people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. These symptoms typically last a few days but may last several weeks. In less than 1% of cases, West Nile virus causes a sometimes life-threatening infection that can make people very sick. Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, and paralysis. The more severe form of the West Nile virus affects mostly older adults. It occurs when the virus crosses the blood-brain barrier and can cause symptoms such as headache, high fever, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, and paralysis. If any of these serious symptoms develop, medical attention should be sought right away.

In summary, the symptoms of West Nile virus can range from no symptoms at all to mild flu-like symptoms to severe illness affecting the central nervous system. If you suspect that you or a family member might have West Nile virus disease, talk with your healthcare provider.