An illness caused by a virus that mosquitoes spread.

West Nile fever is a mild form of disease caused by the West Nile virus. Most people with it recover fully. Very rarely, the virus causes dangerous swelling of the brain or of tissue around the brain and spinal cord.

West Nile fever causes a high temperature, sometimes with headache, body aches or pain, vomiting, diarrhea, or rash. Very rarely, the West Nile virus causes a fever with neck stiffness, shaking, confusion or other serious symptoms.

Treatment for West Nile fever includes rest, fluids and pain medicines bought without a prescription. The rare, serious disease caused by the West Nile virus requires hospital care.