eMedicine Specialties > Physical Medicine and Rehabilitation > Medical Diseases

West Nile Virus

Author: Jess D Salinas Jr, MD, Medical Director, Lake Mary Clinic, National Pain Institute, LLC; Associate Medical Director, Winter Park Clinic, National Pain Institute, LLC
Coauthor(s): Monica L Steiner, MD, Clinical Assistant Professor, Program Director, Department of Orthopedics and Rehabilitation, Loyola University Medical Center
Contributor Information and Disclosures

Updated: Dec 27, 2007

Introduction

Background

The West Nile virus is one of the many members of the genus Flavivirus that are known to cause human disease. The life cycle of the West Nile virus involves the microbe's transmission from nonhuman animals to humans by way of Aedes, Culex, or Anopheles mosquitoes. The West Nile virus can infect horses, birds, dogs, and other mammals.1,2 However, wild birds are apparently the optimal hosts for harboring and replicating the virus.

The West Nile virus has been reported in Africa, Asia, Europe, the Middle East, and North America, where the most recent outbreaks were noted. In 1999, the first cases of West Nile virus disease were reported in New York City, and the infection has been spreading throughout the North American continent ever since.3 In 2002, a total of 3,389 cases were reported in the United States.4,5 Approximately 55% of these cases were from the Midwest (Illinois, Michigan, Ohio, Indiana). (See also the Medscape resource center Emerging and Reemerging Infectious Diseases, as well as the Medscape CME entry Infectious Disease Surveillance: Innovative Strategies and Outcomes.)

The West Nile virus causes serious manifestations in approximately 1% of persons who are infected, with increased morbidity and mortality in individuals older than 50 years. In hospitalized patients in New York City, neurologic sequelae of the West Nile virus included severe muscle weakness, with approximately 10% of patients developing a complete flaccid paralysis.6,7,8 One in 150 West Nile virus infections results in encephalitis or meningitis, and the mortality rate from severe illness is 3-15%. Individuals older than 75 years are at particular risk.1 (See also the eMedicine article West Nile Encephalitis, as well as West Nile Virus-Associated Flaccid Paralysis, on Medscape.)

As the elderly population increases and the distribution of the West Nile virus spreads nationwide, a growing number of infected individuals may require comprehensive inpatient rehabilitation to overcome the virus's disabling effects.9

Frequency

United States

In the Western hemisphere, West Nile virus infection originated in 1999, in New York City. Since then, the disease has occurred with greater frequency in the Southern, Midwestern, and Western states. Symptoms of the infection first appear in the population in early June, with the peak incidence occurring in late August and tapering through early November.

International

The West Nile virus is most commonly identified in Asia, Africa, and the Middle East and is endemic in those parts of the world. In the 1990s, outbreaks of West Nile virus encephalitis were reported in Algeria, the Czech Republic, France, Romania, Russia, and Israel.1

Mortality/Morbidity

  • Reports indicate that less than 1% of persons who are infected with the West Nile virus develop severe illness; of individuals who have severe illness secondary to the infection, 3-15% die.
  • Severe disease particularly affects the elderly. Advanced age is by far the greatest risk factor for neurologic disease, long-term morbidity, and death, especially in persons older than 75 years.

Race

There is no known predisposition related to a particular ethnic group.

Sex

There is no known sex predilection. Men and women are affected equally.

Age

In the United States, the elderly are particularly disposed to illness from West Nile virus infection.

Clinical

History

Mosquito bites may or may not be present in an infected person. A history of travel to or from an area that is known to harbor the virus is common.

The incubation period for the West Nile virus is postulated to be approximately 5-15 days. Symptoms of mild infection may last 3-6 days and include fever in 20% of cases. Other symptoms include nausea, anorexia, malaise, myalgia, headache, backache, rash, eye pain, and vomiting.1

Symptoms of more severe illness include severe muscle weakness, flaccid paralysis, photophobia, seizures, mental status changes, respiratory symptoms, and an erythematous, maculopapular, or morbilliform rash involving the neck, trunk, arms, or legs.6,10 The severity of the illness is related to the degree of central nervous system invasion by the virus.

Physical

Signs of encephalitis and meningoencephalitis may be seen. These include mental status changes, such as confusion, stupor, or coma. Other findings include positive Brudzinski and Kernig signs, papilledema, cranial nerve involvement (eg, facial weakness, double vision, visual loss, decreased taste sensation), motor strength weakness, decreased sensation, hyperreflexia, and positive pathologic reflexes (eg, Babinski sign, Hoffman sign). (See also the eMedicine article Confusional States and Acute Memory Disorders.)

Causes

The West Nile virus is transmitted to humans by the bite of an infected mosquito. Typically, warm climates and the summer months provide an ideal environment for mosquitoes to breed.1 Multiple mosquito bites and greater exposure to environments with a large mosquito population increase the risk of infection. However, some cases have been linked to organ transplantation, breastfeeding, and (possibly) blood transfusions.11

More on West Nile Virus

Overview: West Nile Virus
Differential Diagnoses & Workup: West Nile Virus
Treatment & Medication: West Nile Virus
Follow-up: West Nile Virus
References
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References

  1. Petersen LR, Marfin AA. West Nile virus: a primer for the clinician. Ann Intern Med. Aug 6 2002;137(3):173-9. [Medline]. [Full Text].

  2. Brinton MA. Host factors involved in West Nile virus replication. Ann N Y Acad Sci. Dec 2001;951:207-19. [Medline].

  3. Kramer LD, Bernard KA. West Nile virus in the western hemisphere. Curr Opin Infect Dis. Oct 2001;14(5):519-25. [Medline].

  4. Centers for Disease Control and Prevention. Provisional surveillance summary of the West Nile virus epidemic--United States, January-November 2002. MMWR Morb Mortal Wkly Rep. Dec 20 2002;51(50):1129-33. [Medline].

  5. Centers for Disease Control and Prevention. West Nile virus update--United States, January 1-November 13, 2007. MMWR Morb Mortal Wkly Rep. Nov 16 2007;56(45):1191-2. [Medline].

  6. 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].

  7. Campbell GL, Marfin AA, Lanciotti RS, et al. West Nile virus. Lancet Infect Dis. Sep 2002;2(9):519-29. [Medline].

  8. 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]. [Full Text].

  9. Moorthi S, Schneider WN, Dombovy ML. Rehabilitation outcomes in encephalitis--a retrospective study 1990-1997. Brain Inj. Feb 1999;13(2):139-46. [Medline].

  10. Centers for Disease Control and Prevention. Acute flaccid paralysis syndrome associated with West Nile virus infection--Mississippi and Louisiana, July-August 2002. MMWR Morb Mortal Wkly Rep. Sep 20 2002;51(37):825-8. [Medline].

  11. Centers for Disease Control and Prevention. Update: Investigations of West Nile virus infections in recipients of organ transplantation and blood transfusion--Michigan, 2002. MMWR Morb Mortal Wkly Rep. Oct 4 2002;51(39):879. [Medline].

  12. Sampson BA, Armbrustmacher V. West Nile encephalitis: the neuropathology of four fatalities. Ann N Y Acad Sci. Dec 2001;951:172-8. [Medline].

  13. Greve KW, Houston RJ, Adams D, et al. The neurobehavioural consequences of St. Louis encephalitis infection. Brain Inj. Oct 2002;16(10):917-27. [Medline].

  14. West Nile Virus. Centers for Disease Control and Prevention; [Full Text].

  15. Ahmed S, Libman R, Wesson K, et al. Guillain-Barre syndrome: an unusual presentation of West Nile virus infection. Neurology. Jul 12 2000;55(1):144-6. [Medline].

  16. Anderson JF, Main AJ, Ferrandino FJ, et al. Nocturnal activity of mosquitoes (Diptera: Culicidae) in a West Nile virus focus in Connecticut. J Med Entomol. Nov 2007;44(6):1102-8. [Medline].

  17. Centers for Disease Control and Prevention. Intrauterine West Nile virus infection--New York, 2002. MMWR Morb Mortal Wkly Rep. Dec 20 2002;51(50):1135-6. [Medline].

  18. Katz N, ed. Cognitive Rehabilitation: Models for Intervention in Occupational Therapy. Boston, Mass: Andover Medical Pubs; 1992.

  19. Craven RB, Roehrig JT. West Nile virus. JAMA. Aug 8 2001;286(6):651-3. [Medline].

  20. DeGroote J, Mercer DR, Fisher J, et al. Spatiotemporal investigation of adult mosquito (Diptera: Culicidae) populations in an eastern Iowa County, USA. J Med Entomol. Nov 2007;44(6):1139-50. [Medline].

  21. From the Centers for Disease Control and Prevention. Surveillance for West Nile virus in overwintering mosquitoes--New York, 2000. JAMA. May 10 2000;283(18):2380-1. [Medline]. [Full Text].

  22. Glass JD, Samuels O, Rich MM. Poliomyelitis due to West Nile virus. N Engl J Med. Oct 17 2002;347(16):1280-1. [Medline].

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

  24. Nasci RS, Parise ME, Wirtz RA, et al. Pre- and post-travel general health recommendations. In: Arguin PM, Kozarsky PE, Reed C, eds. CDC Health Information for International Travel. Elsevier; 2007:[Full Text].

  25. Nichter CA, Pavlakis SG, Shaikh U, et al. Rhombencephalitis caused by West Nile fever virus. Neurology. Jul 12 2000;55(1):153. [Medline].

  26. Montgomery J, ed. Physical Therapy for Traumatic Brain Injury. New York, NY: Churchill Livingstone; 1995.

  27. Prigatano GP. Principles of Neuropsychological Rehabilitation. New York, NY: Oxford University Press; 1999.

  28. Samuel CE. Host genetic variability and West Nile virus susceptibility. Proc Natl Acad Sci U S A. Sep 3 2002;99(18):11555-7. [Medline]. [Full Text].

  29. Styer LM, Kent KA, Albright RG, et al. Mosquitoes inoculate high doses of West Nile virus as they probe and feed on live hosts. PLoS Pathog. Sep 14 2007;3(9):1262-70. [Medline]. [Full Text].

  30. Woo BH, Nesathurai S, eds. The Rehabilitation of People with Traumatic Brain Injury. Boston, Mass: Boston Medical Center/Blackwell Science; 2000.

  31. Wang T, Anderson JF, Magnarelli LA, et al. West Nile virus envelope protein: role in diagnosis and immunity. Ann N Y Acad Sci. Dec 2001;951:325-7. [Medline].

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Further Reading

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Keywords

WNV, Flavivirus, encephalitis, meningoencephalitis, West Nile fever, West Nile infection, mosquito bites, Aedes mosquitoes, Culex mosquitoes, Anopheles mosquitoes

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Contributor Information and Disclosures

Author

Jess D Salinas Jr, MD, Medical Director, Lake Mary Clinic, National Pain Institute, LLC; Associate Medical Director, Winter Park Clinic, National Pain Institute, LLC
Jess D Salinas Jr, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Medical Association, and Physiatric Association of Spine, Sports and Occupational Rehabilitation
Disclosure: Emedicine Honoraria Other

Coauthor(s)

Monica L Steiner, MD, Clinical Assistant Professor, Program Director, Department of Orthopedics and Rehabilitation, Loyola University Medical Center
Monica L Steiner, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.

Medical Editor

Elizabeth A Moberg-Wolff, MD, Associate Professor, Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin; Consulting Staff, Department of Physical Medicine and Rehabilitation, Children's Hospital of Wisconsin
Elizabeth A Moberg-Wolff, MD is a member of the following medical societies: American Academy of Cerebral Palsy and Developmental Medicine and American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.

Pharmacy Editor

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

Managing Editor

Kat Kolaski, MD, Assistant Professor, Departments of Orthopedics and Pediatrics, Wake Forest University School of Medicine
Kat Kolaski, MD is a member of the following medical societies: American Academy for Cerebral Palsy and Developmental Medicine, American Academy of Pediatrics, and American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.

CME Editor

Kelly L Allen, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Lourdes Regional Rehabilitation Center, Our Lady of Lourdes Medical Center
Disclosure: Nothing to disclose.

Chief Editor

Consuelo T Lorenzo, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Alegent Health Care, Immanuel Rehabilitation Center
Consuelo T Lorenzo, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.

 
 
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