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West Nile Virus

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What is West Nile virus?

West Nile virus (WNV) is a viral infection spread by mosquitoes. Most people who get the virus (80%) will not develop any symptoms. Some people may experience mild symptoms like body ache, fever, rash or vomiting and diarrhea. These cases usually recover on their own, although fatigue can last for weeks.

A very small subset (about 1 in 150) develop very severe illness that affects the nervous system. This can cause life-threatening brain or spine inflammation. Severe infection is most common in people over 60; however, it can occur in people of any age. Those with compromised immune systems are also at greater risk. Symptoms of severe infection may include:

  • High fever.
  • Headache and neck stiffness.
  • Disorientation.
  • Trembling or convulsions.
  • Muscle weakness.
  • Numbness or paralysis.

Providers must report suspected or confirmed cases of West Nile virus.

WNV should be considered in any cases of febrile or acute neurological illness if the person has had recent exposure to mosquitoes or received donated blood or organs.  This is especially true in summer or early fall, or if patients visited areas where virus activity has been reported.

To report a case, visit our Report Notifiable Conditions page or call (253) 798-6534.

Resources for providers