eMedicine Specialties > Infectious Diseases > CNS Infections

West Nile Encephalitis

Author: Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Contributor Information and Disclosures

Updated: Aug 1, 2008

Introduction

Background

West Nile encephalitis (WNE) is distinguished from other arthropod-borne causes of viral encephalitis (eg, western equine encephalitis, eastern equine encephalitis [EEE], Japanese encephalitis, Venezuelan encephalitis) based on its geographic distribution, clinical features, and laboratory findings.

WNE is endemic in the Middle East, Africa, and Asia. In North America, WNE first occurred in the northeast United States along the eastern seaboard and now extends nationwide. WNE may have existed in antiquity in the Middle East. Some have suggested that Alexander the Great may have died from WNE.1,2

Seventeen species of wild birds transmit 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.

Pathophysiology

WNE, as with other arthropod-borne viral encephalitides, 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).

Frequency

United States

Cases of WNE in the United States initially occurred mostly in the greater New York area, but cases have now occurred in western states. Wild birds with West Nile virus have been found in various states and Canada.

Furthermore, the cluster of recent outbreaks in Romania, Russia, the Congo, and the United States is characterized by a low frequency of classic WNE features but a high rate of encephalitis and death.

Most exposures to West Nile virus result in asymptomatic seroconversion.

International

Approximately 50% of children in Egypt have West Nile virus seropositivity. WNE is the most common cause of viral aseptic meningitis or encephalitis in patients presenting to emergency departments in Cairo. WNE is common in the Middle East, Asia, and Africa.

Mortality/Morbidity

Most children with WNE in Asia and Africa have a benign course and only rarely die of the disease. In the United States, most fatal cases have occurred in elderly patients.

Race

WNE has no racial predisposition.

Sex

WNE is equally common in males and females.

Age

Most US cases occur in elderly patients. Worldwide, most cases occur in young children or young adults; however, elderly patients are affected more severely.

Clinical

History

  • Mosquito bites: Patients may not provide a mosquito bite history. The incubation period of West Nile encephalitis (WNE) is 1-6 days, perhaps as long as 14 days in immunosuppressed patients.
  • Symptoms
    • Most people who are infected (at least most children) are asymptomatic or have a flulike illness. A minority of people develop neurologic disease.
    • Many patients describe prominent GI symptoms, especially vomiting and diarrhea.
    • Nonspecific symptoms may include sore throat, backache, myalgias, and arthralgias.
    • Most patients with WNE present with features of encephalitis, aseptic meningitis (meningoencephalitis), or both.
    • Symptoms include a mild febrile illness accompanied by headache, mental confusion, tremors, or flaccid paralysis.
    • Symptoms are most prominent in very young and very old people.

Physical

  • The extent and severity of CNS viral invasion determine the clinical expression of WNE.
  • Most patients are febrile or have low-grade fevers.
  • Patients who present with encephalitis have mental confusion or disorientation and may have decreased consciousness. Patients with severe cases of WNE may present with stupor or coma.
  • Multifocal chorioretinitis is the most common ophthalmologic manifestation of WNE.
  • Ten percent of patients with WNE have an enlarged liver. Approximately 20% have splenomegaly.
  • CNS findings include a stiff neck with meningeal signs, including positive Kernig or Brudzinski signs in patients with aseptic meningitis or meningoencephalitis.
  • Some cases of WNE are accompanied by mild nonexudative pharyngitis.
  • In a 2001 study, approximately 20% of patients infected with West Nile virus in New York City presented with truncal maculopapular rash.3  
  • Generalized adenopathy and an enlarged submental node are uncommon (1%).3
  • Consider WNE in patients who have encephalitis and otherwise unexplained extremity weakness and/or paralysis.

Causes

  • WNE usually occurs in the summer, when mosquitoes, wild migratory birds, and humans are in close proximity outdoors.
  • Mosquito bites, which are particularly likely during feeding times (dawn and dusk) in the summer months, transmit West Nile virus.
  • Prolonged contact or multiple mosquito bites enhances the risk.
  • West Nile virus may be transmitted in organ transplants.
  • West Nile virus has been found in breast milk.

More on West Nile Encephalitis

Overview: West Nile Encephalitis
Differential Diagnoses & Workup: West Nile Encephalitis
Treatment & Medication: West Nile Encephalitis
Follow-up: West Nile Encephalitis
Multimedia: West Nile Encephalitis
References
[ CLOSE WINDOW ]

References

  1. Cunha BA. Alexander the Great and West Nile virus encephalitis. Emerg Infect Dis. Jul 2004;10(7):1328-9; author reply 1332-3. [Medline].

  2. Oldach D, Benitez RM, Mackowiak PA. Alexander the Great and West Nile virus encephalitis. Emerg Infect Dis. Jul 2004;10(7):1329-30; author reply 1332-3. [Medline].

  3. Nash D, Mostashari F, Fine A, et al. The outbreak of West Nile virus infection in the New York City area in 1999. N Engl J Med. Jun 14 2001;344(24):1807-14. [Medline].

  4. Abroug F, Ouanes-Besbes L, Letaief M, et al. A cluster study of predictors of severe West Nile virus infection. Mayo Clin Proc. Jan 2006;81(1):12-6. [Medline].

  5. 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. Mar 2000;30(3):413-8. [Medline].

  6. Bailey EM, Domenico P, Cunha BA. Bacterial or viral meningitis? Measuring lactate in CSF can help you know quickly. Postgrad Med. Oct 1990;88(5):217-9, 223. [Medline].

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

  8. CDC. Outbreak of West Nile-like viral encephalitis--New York, 1999. MMWR Morb Mortal Wkly Rep. Oct 1 1999;48(38):845-9. [Medline].

  9. Cunha BA. Antibiotic Essentials. 5th ed. Royal Oak, Mich: Physician's Press; 2006.

  10. Cunha BA. The diagnosis and therapy of acute bacterial meningitis. In: Central Nervous System Infections. Berlin: Spinger-Verlag; 1990:3-24.

  11. Cunha BA. Differential diagnosis of West Nile encephalitis. Curr Opin Infect Dis. Oct 2004;17(5):413-20. [Medline].

  12. Cunha BA. Eastern Equine Encephalitis. Infect Dis Pract. 1996;20:75-79.

  13. Cunha BA. Encephalitis. Infect Dis Pract. 1989;12:1-12.

  14. Cunha BA. The diagnostic significance of RBCs in the CSF. Infect Dis Pract. 1997;21:30.

  15. Cunha BA, Filozov A, Remé P. Listeria monocytogenes encephalitis mimicking West Nile encephalitis. Heart Lung. Jan-Feb 2004;33(1):61-4. [Medline].

  16. Cunha BA, McDermott BP, Mohan SS. Prognostic importance of lymphopenia in West Nile encephalitis. Am J Med. Nov 1 2004;117(9):710-1. [Medline].

  17. Cunha BA, Minnaganti V, Johnson DH, et al. Profound and prolonged lymphocytopenia with West Nile encephalitis. Clin Infect Dis. Oct 2000;31(4):1116-7. [Medline].

  18. Cunha BA, Sachdev B, Canario D. Serum ferritin levels in West Nile encephalitis. Clin Microbiol Infect. Feb 2004;10(2):184-6. [Medline].

  19. Cunha BA, Thermidor M, Mohan S, Ly H. West Nile viral encephalitis mimicking hepatic encephalopathy. Heart Lung. Jan-Feb 2005;34(1):72-5. [Medline].

  20. Cunha BA. Clinical Approach in Encephalitis. In: Halperin JJ. Encephalitis: Diagnosis and Treatment. New York, NY: Informa Healthcare; 2008:1-18.

  21. Darwish MA, Ibrahim AH. Prevalence of antibodies to arboviruses in Egypt. Results of a serologic survey among 1,113 university students. Am J Trop Med Hyg. Nov 1975;24(6 Pt 1):981-5. [Medline].

  22. Dean JL, Palermo BJ. West Nile Virus Encephalitis. Curr Infect Dis Rep. Jul 2005;7(4):292-296. [Medline].

  23. Flatau E, Kohn D, Daher O, et al. West Nile fever encephalitis. Isr J Med Sci. Nov 1981;17(11):1057-9. [Medline].

  24. Gadoth N, Weitzman S, Lehmann EE. Acute anterior myelitis complicating West Nile fever. Arch Neurol. Mar 1979;36(3):172-3. [Medline].

  25. Goldblum N, Jasinska-Klingberg W, Klingberg MA, Mareberg K, Sterk VV. The natural history of West Nile Fever. I. Clinical observations during an epidemic in Israel. Am J Hyg. Nov 1956;64(3):259-69. [Medline].

  26. Goldblum N, Sterk VV, Paderski B. West Nile fever; the clinical features of the disease and the isolation of West Nile virus from the blood of nine human cases. Am J Hyg. Jan 1954;59(1):89-103. [Medline].

  27. Gubler DJ. The continuing spread of West Nile virus in the western hemisphere. Clin Infect Dis. Oct 15 2007;45(8):1039-46. [Medline].

  28. Han LL, Popovici F, Alexander JP Jr, et al. Risk factors for West Nile virus infection and meningoencephalitis, Romania, 1996. J Infect Dis. Jan 1999;179(1):230-3. [Medline].

  29. Ho M. Acute viral encephalitis. In: Handbook of Clinical Neurology. Infections of the Nervous System. Springer-Verlag; 1978:63-82.

  30. Hubálek Z. Comparative symptomatology of West Nile fever. Lancet. Jul 28 2001;358(9278):254-5. [Medline].

  31. Jamison SC, Michaels SR, Ratard R, et al. A 41-year-old HIV-positive man with acute onset of quadriplegia after West Nile virus infection. South Med J. Oct 2007;100(10):1051-3. [Medline].

  32. Jeyakumar A, Hindenburg A, Minnaganti VR, et al. West Nile virus encephalitis mimicking central nervous system metastases from small cell lung cancer. Am J Med. Nov 2003;115(7):594-5. [Medline].

  33. Klein NC, Johnson DH, Cunha BA. West Nile Virus in Nassau County, New York: The Long Island Experience. Infect Dis Clin Pract. 2000;9:303-308.

  34. Monath TP. Flaviviruses. In: Knipe DM, Howley PM, eds. Fields: Virology. 2nd ed. New York, NY: Raven Press; 1990:763-814.

  35. Monath TP, Tsai TF. Flaviviruses. In: Richman DD, Whitley RJ, eds. Clinical Virology. New York, NY: Churchill Livingstone; 1997:1133-1185.

  36. Murray K, Baraniuk S, Resnick M, Arafat R, Kilborn C, Cain K, et al. Risk factors for encephalitis and death from West Nile virus infection. Epidemiol Infect. Dec 2006;134(6):1325-32. [Medline].

  37. Murray KO, Resnick M, Miller V. Depression after infection with West Nile virus. Emerg Infect Dis. Mar 2007;13(3):479-81. [Medline].

  38. Natarajan N, Varman M. West Nile virus cerebellitis in a healthy 10-year-old child. Pediatr Infect Dis J. Aug 2007;26(8):767. [Medline].

  39. Ou AC, Ratard RC. One-year sequelae in patients with West Nile Virus encephalitis and meningitis in Louisiana. J La State Med Soc. Jan-Feb 2005;157(1):42-6. [Medline].

  40. Perelman A, Stern J. Acute pancreatitis in West Nile Fever. Am J Trop Med Hyg. Nov 1974;23(6):1150-2. [Medline].

  41. Pruzanski W, Altman R. Encephalitis due to West Nile fever virus. World Neurol. Jun 1962;3:524-8. [Medline].

  42. Ravindra KV, Freifeld AG, Kalil AC, et al. West Nile virus-associated encephalitis in recipients of renal and pancreas transplants: case series and literature review. Clin Infect Dis. May 1 2004;38(9):1257-60. [Medline].

  43. Rawal A, Gavin PJ, Sturgis CD. Cerebrospinal fluid cytology in seasonal epidemic West Nile virus meningo-encephalitis. Diagn Cytopathol. Feb 2006;34(2):127-9. [Medline].

  44. Rios M, Daniel S, Chancey C, et al. West Nile virus adheres to human red blood cells in whole blood. Clin Infect Dis. Jul 15 2007;45(2):181-6. [Medline].

  45. Rodriguez AJ, Westmoreland BF. Electroencephalographic characteristics of patients infected with west nile virus. J Clin Neurophysiol. Oct 2007;24(5):386-9. [Medline].

  46. Roos KL. West Nile encephalitis and myelitis. Curr Opin Neurol. Jun 2004;17(3):343-6. [Medline].

  47. Sejvar JJ. The long-term outcomes of human West Nile virus infection. Clin Infect Dis. Jun 15 2007;44(12):1617-24. [Medline].

  48. Sherman-Weber S, Axelrod P. Central diabetes insipidus complicating West Nile encephalitis. Clin Infect Dis. Apr 1 2004;38(7):1042-3. [Medline].

  49. Shoji H, Azuma K, Nishimura Y, et al. Acute viral encephalitis: the recent progress. Intern Med. Jun 2002;41(6):420-8. [Medline].

  50. Smithburn KC, Hughes TP, Burke AW. A neurotropic virus isolated from the blood of a native of Uganda. Am J Trop Med Hyg. 1940;20:471-492.

  51. Southam CM, Moore AE. Induced virus infections in man by the Egypt isolates of West Nile virus. Am J Trop Med Hyg. Jan 1954;3(1):19-50. [Medline].

  52. Taylor RM, Work TH, Hurlbutt HS, et al. A study of the ecology of West Nile virus in Egypt. Am J Trop Med Hyg. Jul 1956;5(4):579-620. [Medline].

  53. Truemper EJ, Romero JR. West Nile Virus. Pediatr Ann. Jul 2007;36(7):414-22. [Medline].

  54. Tsai TF, Popovici F, Cernescu C, et al. West Nile encephalitis epidemic in southeastern Romania. Lancet. Sep 5 1998;352(9130):767-71. [Medline].

  55. Tyler KL, Pape J, Goody RJ, et al. CSF findings in 250 patients with serologically confirmed West Nile virus meningitis and encephalitis. Neurology. Feb 14 2006;66(3):361-5. [Medline].

  56. Wadei H, Alangaden GJ, Sillix DH, et al. West Nile virus encephalitis: an emerging disease in renal transplant recipients. Clin Transplant. Dec 2004;18(6):753-8. [Medline].

[ CLOSE WINDOW ]

Further Reading

[ CLOSE WINDOW ]

Keywords

West Nile encephalitis, WNE, West Nile virus encephalitis, WNVE, West Nile virus, viral encephalitis, western equine encephalitis, WEE, eastern equine encephalitis, EEE, Japanese encephalitis, Venezuelan encephalitis

[ CLOSE WINDOW ]

Contributor Information and Disclosures

Author

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

Wesley W Emmons, MD, FACP, Assistant Professor, Department of Medicine, Thomas Jefferson University; Consulting Staff, Infectious Diseases Section, Department of Internal Medicine, Christiana Care, Newark, DE
Wesley W Emmons, MD, FACP is a member of the following medical societies: American College of Physicians, American Medical Association, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, and International AIDS Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

John L Brusch, MD, FACP, Assistant Professor of Medicine, Harvard Medical School; Consulting Staff, Department of Medicine and Infectious Disease Service, Cambridge Health Alliance
John L Brusch, MD, FACP is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD, Professor, Stewart G Wolf Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center
Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physician Executives, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Federation for Clinical Research, American Medical Association, American Society for Microbiology, Association of Professors of Medicine, Association of Program Directors in Internal Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

 
 
HONcode

We subscribe to the
HONcode principles of the
Health On the Net Foundation

All material on this website is protected by copyright, Copyright© 1994- by Medscape.
This website also contains material copyrighted by 3rd parties.

DISCLAIMER: The content of this Website is not influenced by sponsors. The site is designed primarily for use by qualified physicians and other medical professionals. The information contained herein should NOT be used as a substitute for the advice of an appropriately qualified and licensed physician or other health care provider. The information provided here is for educational and informational purposes only. In no way should it be considered as offering medical advice. Please check with a physician if you suspect you are ill.