A mosquito-transmitted virus causes most cases of West Nile infection. Most people infected with West Nile virus either don't develop signs or symptoms or have only minor ones, such as fever and mild headache. However, some people develop a life-threatening illness that includes inflammation of the spinal cord or brain.
Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a severe headache, fever, disorientation or sudden weakness — require immediate attention.
Exposure to mosquitoes where West Nile virus exists increases your risk of getting infected. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.