About 80% of people infected with the virus have no symptoms. Those who do usually start to feel sick 3 to 14 days after being bitten by an infected mosquito. Most people who get sick develop West Nile fever. Symptoms include fever, headache, fatigue, body aches, muscle pain, joint pain, and chills. More than half of sick people report a rash. Symptoms usually last for 3 to 6 days but some people have been sick for weeks. A few people (approximately 1 in 150 infected persons) develop severe disease with serious symptoms. The virus invades the nervous system, causing encephalitis (inflammation of the brain) or meningitis (inflammation of the tissues surrounding the brain and spinal cord). Symptoms of severe disease include headache, fever, stiff neck, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Severe disease may last for weeks and cause permanent injury or, in some cases, death.