West Nile Encephalitis

National Organization for Rare Disorders, Inc.

Skip to the navigation


It is possible that the main title of the report West Nile Encephalitis is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • West Nile Fever
  • Kunjin fever
  • WNE
  • West Nile virus
  • Viral encephalitis
  • Western equine encephalitis
  • WEE
  • Eastern equine encephalitis
  • EEE
  • Japanese encephalitis
  • Venezuelan encephalitis

Disorder Subdivisions

  • None

General Discussion

There are seventeen species of birds that are the known carriers of and transmit West Nile Encephalitis (WNE) to humans via the Culex, Aedes, and Anopheles mosquitoes. WNE first causes symptomatic or asymptomatic illness in wild migratory birds that act as viral replication factories. Wild birds infected with WNE contain high titers of the virus and remain viremic for 1-2 weeks, making them ideal hosts to perpetuate the disease. Mosquitoes transmit WNE from birds to humans. Horses, dogs, and other small animals may harbor WNE after being bitten; however, they are inefficient transmitters because viral titers are relatively low, and WNE viremia is short-lived in these animals.


Patients with WNE may present with a wide range of severity in symptoms and may features of encephalitis, aseptic meningitis (meningoencephalitis), or both. It is common for patients to have a mild febrile illness accompanied by headache, mental confusion, tremors, or flaccid paralysis. Symptoms are most obvious in people who are very young and people who are elderly. Many people who are infected (at least most children) are also often asymptomatic or have a nonspecific flu-like illness. A minority of people may develop neurologic disease.

The extent and severity of viral invasion of the central nervous system (CNS) determine the clinical expression of WNE. Most patients are febrile or have low-grade fevers. Patients presenting with encephalitis have mental confusion or disorientation and may have decreased consciousness. Patients with severe cases of WNE may present with stupor or coma. The most common ophthalmic manifestation for WNE is chorioretinitis and about 10% of patients have an enlarged liver and spelnomegaly. CNS findings include a stiff neck with meningeal signs, including positive Kernig or Brudzinski signs in patients with aseptic meningitis or meningoencephalitis. Generalized adenopathy and an enlarged submental node are also very common.


Mosquito bites are the main culprits for the spread of WNE with an incubation period of WNE is 1-6 day but many patients may not provide a mosquito bite history. WNE usually occurs in the summer when mosquitoes, wild migratory birds, and humans are in close proximity outdoors. Mosquito bites, which are particularly prone to occur during feeding times (dawn and dusk) in the summer months, transmit WNE and prolonged contact or multiple mosquito bites enhances risk.

WNE may be transmitted in organ transplants and WNE virus has been found in breast milk.

WNE, as with other arthropod-borne viral encephalitis, traverses the blood-brain barrier and infects the brain parenchyma, clinically manifesting as viral encephalitis. WNE may also affect the leptomeninges, resulting in a clinical presentation of aseptic meningitis (viral meningitis). Patients with WNE may present with features of both encephalitis and aseptic meningitis (meningoencephalitis).

Affected Populations

In the US the initial cases of WNE were first identified in the greater New York area, but cases have now occurred in western states. Wild birds with WNE virus have also been identified in parts of Canada. WNE is common in the Middle East, Asia, and Africa WNE seropositivity of children in Egypt is approximately 50%. WNE is the most common cause of viral aseptic meningitis or encephalitis in patients presenting to emergency departments in Cairo. Both sexes are affected equally and it is more frequent in elderly patients.

Standard Therapies


Electroencephalogram: This is the most sensitive way to make a presumptive diagnosis of HSV-1 encephalitis. An abnormal temporal lobe focus is present on EEG as early as the first few days of the disease.

EEG shows unilateral focal electrical abnormalities in the temporal lobe.

Lumbar puncture: CSF reveals mild-to-moderate pleocytosis with a lymphocytic predominance in WNE. CSF protein is variably elevated, and the CSF glucose level is not decreased.

The CSF lactic acid level is not elevated, and RBCs, excluding traumatic taps, are not present in WNE. CSF Gram stain and bacterial culture findings are negative.

Medical Care:

Provide supportive care to minimize the potential for cerebral edema. In comatose patients, pay special attention to maintaining a clear airway. Fluid replacement is also essential.

Surgical Care:

No surgical care is necessary.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:




Asnis DS, Conetta R, Teixeira AA, et al: The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience. Clin Infect Dis 2000 Mar; 30(3): 413-8

Batuello JT, Youngwerth J, Gabel R: Increased serum lipase in West Nile virus infection. N Engl J Med 2005 Jan 27; 352(4): 420-1

Cunha BA, Sachdev B, Canario D: Serum ferritin levels in West Nile encephalitis. Clin Microbiol Infect 2004; 10: 184-186.

Bréhin AC, Mouriès J, Frenkiel MP, Dadaglio G, Desprès P, Lafon M, Couderc T. Dynamics of Immune Cell Recruitment during West Nile Encephalitis and Identification of a New CD19+B220-BST-2+ Leukocyte Population. J Immunol. 2008 May 15;180 (10):6760-7.

Donoso Mantke O, Vaheri A, Ambrose H, Koopmans M, de Ory F, Zeller H, Beyrer K, Windorfer A, Niedrig M; European Network for Diagnostics of Imported Viral Diseases (ENIVD) Working Group for Viral CNS Diseases. Analysis of the surveillance situation Euro Surveill. 2008 Jan 17;13(3) pii: 8017.

Widman DG, Ishikawa T, Fayzulin R, Bourne N, Mason PW. Construction and characterization of a second-generation pseudoinfectious West Nile virus vaccine propagated using a new cultivation system. Vaccine. 2008 Mar 31.

Monreal R, Vega A, Simeone F, Hamm L, Palacios E, Maylin M, Lopez FA.

An immunosuppressed woman presenting with acute flaccid paralysis and progressive respiratory failure. J La State Med Soc. 2007 Nov-Dec;159(6):298-303; quiz 304, 342.

Takasaki T. [West Nile fever/encephalitis] Uirusu. 2007 Dec;57(2):199-205. Review. Japanese.

Goody RJ, Schittone SA, Tyler KL. Experimental reovirus-induced acute flaccid paralysis and spinal motor neuron cell death.

J Neuropathol Exp Neurol. 2008 Mar;67(3):231-9.

Shrestha B, Ng T, Chu HJ, Noll M, Diamond MS.The relative contribution of antibody and CD8(+) T cells to vaccine immunity against West Nile encephalitis virus.

Vaccine. 2008 Apr 7;26(16):2020-33. Epub 2008 Feb 20.

Patiris PJ, Oceguera LF 3rd, Peck GW, Chiles RE, Reisen WK, Hanson CV. Serologic diagnosis of West Nile and St. Louis encephalitis virus infections in domestic chickens.

Am J Trop Med Hyg. 2008 Mar;78 (3):434-41.

Wittich CA, Ward MP, Fosgate GT, Srinivasan R. Identification of hyperendemic foci of horses with West Nile virus disease in Texas. Am J Vet Res. 2008 Mar; 69(3):378-84.

Klinkhamer K, Lipman LJ. [Introduction of West Nile virus in the Netherlands]

Tijdschr Diergeneeskd. 2008 Feb 1;133(3):106-7. Review. Dutch.

Hall DA, Tyler KL, Frey KL, Kozora E, Arciniegas DB. Persistent neurobehavioral signs and symptoms following West Nile fever.

J Neuropsychiatry Clin Neurosci. 2008 Winter;20(1):122-3.

Douglas KO, Kilpatrick AM, Levett PN, Lavoie MC. A quantitative risk assessment of West Nile virus introduction into Barbados.West Indian Med J. 2007 Oct;56(5):394-7.

McMurtrey CP, Lelic A, Piazza P, Chakrabarti AK, Yablonsky EJ, Wahl A, Bardet W, Eckerd A, Cook RL, Hess R, Buchli R, Loeb M, Rinaldo CR, Bramson J, Hildebrand WH. Epitope discovery in West Nile virus infection: Identification and immune recognition of viral epitopes. Proc Natl Acad Sci U S A. 2008 Feb 26;105(8):2981-6. Epub 2008 Feb 25.

Rison RA. Re: Modafinil for treatment of fatigue in post-polio syndrome: a randomized controlled trial.

Neurology. 2008 Feb 26;70(9):736-7; author reply 737-8. No abstract available.

PMID: 18299530

Hamer GL, Kitron UD, Brawn JD, Loss SR, Ruiz MO, Goldberg TL, Walker ED. Culex pipiens (Diptera: Culicidae): a bridge vector of West Nile virus to humans. J Med Entomol. 2008 Jan;45(1):125-8.

Gerry AC, Nawaey TM, Sanghrajka PB, Wisniewska J, Hullinger P. Hematophagous Diptera collected from a horse and paired carbon dioxide-baited suction trap in southern California: relevance to West Nile virus epizootiology. J Med Entomol. 2008 Jan;45(1):115-24.


Transverse Myelitis Association

1787 Sutter Parkway

Powell, OH 43065-8806


Tel: (614)766-1806

Email: info@myelitis.org

Internet: http://www.myelitis.org

Centers for Disease Control and Prevention

1600 Clifton Road NE

Atlanta, GA 30333

Tel: (404)639-3534

Tel: (800)232-4636

TDD: (888)232-6348

Email: cdcinfo@cdc.gov

Internet: http://www.cdc.gov/

NIH/National Institute of Allergy and Infectious Diseases

NIAID Office of Communications and Government Relations

5601 Fishers Lane, MSC 9806

Bethesda, MD 20892-9806

Tel: (301)496-5717

Fax: (301)402-3573

Tel: (866)284-4107

TDD: (800)877-8339

Email: ocpostoffice@niaid.nih.gov

Internet: http://www.niaid.nih.gov/

NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801

Bethesda, MD 20824

Tel: (301)496-5751

Fax: (301)402-2186

Tel: (800)352-9424

TDD: (301)468-5981

Internet: http://www.ninds.nih.gov/

Encephalitis Global

18 North Broadway #404

Tarrytown, NY 10591


Tel: 604-980-2236

Fax: (604)904-0809

Email: admin@encephalitisglobal.org

Internet: http://www.encephalitisglobal.org

Encephalitis Society

32 Castlegate


North Yorkshire, YO17 7DT

United Kingdom

Tel: 4401653692583

Internet: http://www.encephalitis.info

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223

Internet: http://rarediseases.info.nih.gov/GARD/

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into myCigna.com. For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html.