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West Nile Virus

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West Nile Virus

  • West Nile Virus Home
  • About West Nile Virus
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  • For Health Professionals

Related Topics

  • Diseases Transmitted by Mosquitoes
  • Infectious Diseases A-Z
  • Reportable Infectious Diseases
Contact Info
Infectious Disease Epidemiology, Prevention and Control Division
651-201-5414
IDEPC Comment Form

Contact Info

Infectious Disease Epidemiology, Prevention and Control Division
651-201-5414
IDEPC Comment Form

About West Nile Virus

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

Fact Sheet

  • West Nile Encephalitis Fact Sheet (PDF)
    Answers to frequently asked questions about West Nile encephalitis.
    • Hmong (PDF)
    • Karen (PDF)
    • Somali (PDF)
    • Spanish (PDF)
       

Transmission

  • West Nile is one of several mosquitoborne diseases that have been seen in Minnesota.

Prevention

  • 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

  • CDC: West Nile Virus: What You Need To Know
    CDC Factsheet.

 

Tags
  • westnile
Last Updated: 06/12/2025

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