The majority of people infected with West Nile virus will be nonsymptomatic.

An estimated 20% of those infected with West Nile virus will have mild flu-like symptoms including:

• Fever

• Fatigue

• Headache

• Body aches

• Swollen lymph nodes

• Body rash

An estimated 1 in 150 people infected with West Nile virus will progress to a more severe infection called West Nile neuro-invasive disease (menigitis, encephalitis, and poliomyelitis) with symptoms including:

• Headache

• High fever

• Stiff neck

• Disorientation

• Stupor

• Tremors

• Seizures or convulsions

• Paralysis

• Coma

• Death

The incubation period for West Nile neuro-invasive disease and/or fever is 3 to 14 days.  The incubation period is defined as the period of time from when a person acquires the infection to the onset of his or her symptoms.

Symptoms of West Nile virus usually last for only a few days, although severe disease symptoms may last weeks.  Some neurological effects may be permanent.