Most have no symptoms
Most people infected with the West Nile virus have no signs or symptoms.

Mild infection signs and symptoms
About 20 percent of people develop a mild infection called West Nile fever. Common signs and symptoms of West Nile fever include:

    Fever
    Headache
    Body aches
    Fatigue
    Skin rash (occasionally)
    Swollen lymph glands (occasionally)
    Eye pain (occasionally)

Serious infection signs and symptoms
In less than 1 percent of infected people, the virus causes a serious neurological infection. Such infection may include inflammation of the brain (encephalitis) or of the brain and surrounding membranes (meningoencephalitis). Serious infection may also include infection and inflammation of the membranes surrounding the brain and spinal cord (meningitis), inflammation of the spinal cord (West Nile poliomyelitis) and acute flaccid paralysis — a sudden weakness in your arms, legs or breathing muscles. Signs and symptoms of these diseases include:

    High fever
    Severe headache
    Stiff neck
    Disorientation or confusion
    Stupor or coma
    Tremors or muscle jerking
    Lack of coordination
    Convulsions
    Pain
    Partial paralysis or sudden weakness

Signs and symptoms of West Nile fever usually last a few days, but sign and symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.

When to see a doctor
Mild symptoms of West Nile fever usually resolve on their own. If you experience signs or symptoms of serious infection, such as severe headaches, a stiff neck or an altered mental state, seek medical attention right away. A serious West Nile virus infection generally requires hospitalization.