About West Nile Virus - Minnesota Dept. of Health

About West Nile Virus

On this page:
Fact Sheet
Signs and symptoms
More from other websites

Fact Sheet



  • Preventing Mosquitoborne Diseases
    Learn how to minimize your risk to West Nile and other diseases transmitted by mosquitoes.

  • There is a vaccine available to prevent West Nile encephalitis in horses. Please contact your veterinarian for vaccine recommendations. A human West Nile vaccine is still in development.

Signs and symptoms

The typical incubation period for West Nile is 2-6 days, although it can be as long as 15 days.

  • Most people infected with West Nile virus will be asymptomatic or experience a flu-like illness

  • 20% of those bitten by an infected mosquito will develop the symptoms of West Nile fever

  • 1 out of 150 people bitten by an infected mosquito will develop the more severe form of West Nile, West Nile encephalitis

West Nile fever

  • West Nile fever symptoms include:
    • sudden onset of high fever (usually >102°F)
    • severe headache
    • nausea
    • vomiting
    • sore throat
    • backache
    • joint pain
    • prominent muscle aches and weakness
    • prolonged fatigue
    • rash (more commonly associated with West Nile fever than encephalitis)
    • swollen lymph nodes

West Nile encephalitis

Less than 1% of those infected with West Nile will develop severe neurological symptoms consistent with encephalitis or meningitis.

  • West Nile encephalitis symptoms include:
    • mental status changes
    • vomiting
    • sensitivity to light
    • altered reflexes
    • seizures (less frequent)
    • 15% progress to coma
    • Acute flaccid paralysis (AFP) occurs in a small percentage of severely affected patients

The death rate among those showing symptoms of severe West Nile infection (encephalitis or meningitis) is around 10%. Most severe cases occur in elderly people.

More information

Updated Thursday, 09-Jan-2020 09:36:46 CST