Mississippi State Department of Health

West Nile Virus Information for Clinicians
Fact sheet from the CDC


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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