Mississippi State Department of Health

West Nile Virus Information for Clinicians
Fact sheet from the CDC

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Clinical Features

Mild Infection

Most WNV infections are mild and often clinically unapparent.

Reports from earlier outbreaks describe the mild form of WNV infection as a febrile illness of sudden onset often accompanied by

  • malaise
  • headache
  • nausea
  • rash
  • vomiting
  • anorexia
  • myalgia
  • lymphadenopathy
  • eye pain

The full clinical spectrum of West Nile fever has not been determined in the United States.

Severe Infection

Approximately 1 in 150 infections will result in severe neurological disease.

In recent outbreaks, symptoms occurring among patients hospitalized with severe disease include:

  • fever
  • gastrointestinal symptoms
  • weakness
  • change in mental status
  • ataxia and extrapyramidal signs
  • optic neuritis
  • cranial nerve abnormalities
  • polyradiculitis
  • myelitis
  • seizures

Although not observed in recent outbreaks, myocarditis, pancreatitis, and fulminant hepatitis have been described.

Clinical Suspicion

Diagnosis of WNV infection is based on a high index of clinical suspicion and obtaining specific laboratory tests.

Note: Severe neurological disease due to WNV infection has occurred in patients of all ages. Year-round transmission is possible in some areas. Therefore, WNV should be considered in all persons with unexplained encephalitis and meningitis.


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