West Nile virus

Last reviewed: 6 Jun 2022
Last updated: 20 Sep 2019



History and exam

Key diagnostic factors

  • fever of sudden onset
  • malaise
  • myalgia
  • arthralgia
  • pharyngitis
  • anorexia
  • abdominal pain
  • visual disturbances
  • headache
  • rash
  • lymphadenopathy
  • conjunctival injection
  • multi-focal chorioretinal lesions
  • chorioretinitis and inflammatory vitritis
  • seizures
  • respiratory distress
  • jaundice
  • epigastric tenderness
  • mild confusion
  • disorientation
  • stupor/coma
  • neck stiffness
  • Kernig's sign
  • Brudzinski's sign
  • muscle paralysis
  • parkinsonism
  • ataxia
  • myoclonus
  • tremors
More key diagnostic factors

Other diagnostic factors

  • nausea/vomiting
  • generalised muscle weakness
  • splenomegaly
  • retinal haemorrhages
  • chest pain, dyspnoea, palpitations
  • photophobia
  • depression
  • loss of memory
  • bowel and bladder dysfunction
  • cranial nerve palsies
Other diagnostic factors

Risk factors

  • living in/visiting areas with high West Nile virus activity
  • mosquito bites
  • blood transfusion
  • organ transplant
  • needle-stick injuries
More risk factors

Diagnostic investigations

1st investigations to order

  • serology
  • cerebrospinal fluid (CSF) analysis
  • full blood count
  • serum electrolytes
  • liver function tests
  • serum amylase/lipase
More 1st investigations to order

Investigations to consider

  • MRI brain
  • CT head
  • viral culture or reverse transcriptase-polymerase chain reaction (RT-PCR)
More investigations to consider

Treatment algorithm


West Nile fever

West Nile neuroinvasive disease



Bruce Y. Lee, MD, MBA
Bruce Y. Lee

Associate Professor of International Health


Global Obesity Prevention Center

Director of Operations Research

International Vaccine Access Center (IVAC)

Johns Hopkins School of Public Health




BYL declares that he has no competing interests.

Peer reviewers

Susan Stramer, PhD

Executive Scientific Officer

American Red Cross




SS declares that she has no competing interests.

  • Differentials

    • Herpes simplex encephalitis
    • St. Louis encephalitis
    • Eastern equine encephalitis
    More Differentials
  • Guidelines

    • West Nile virus: epidemiology, diagnosis and prevention
    • West Nile virus in the United States: guidelines for surveillance, prevention, and control
    More Guidelines
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