West Nile virus

Last reviewed: 5 Jan 2023
Last updated: 19 Jul 2022



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

Professor of Health Policy and Management

Executive Director

Center for Advanced Technology and Communication for Health (CATCH)

Public Health Informatics Computational and Operation Research (PHICOR)

City University of New York (CUNY)

New York



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
    • A guide to utilization of the microbiology laboratory for diagnosis of infectious diseases
    More Guidelines
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