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West Nile Virus and West Nile Encephalitis (WNE)

West Nile Virus Facts

  • West Nile virus is transmitted to humans by mosquito bites and may cause encephalitis (West Nile encephalitis or WNE) in a few patients.
  • West Nile virus usually occurs in birds but can be transmitted by a mosquito vector to humans.
  • Symptoms of West Nile viral infections may range from no symptoms to fever, chills, muscle aches, headaches, and sensitivity to light; severe infections may cause additional symptoms associated with meningitis, encephalitis, coma, seizures, and infrequently, death.
  • West Nile virus infections are diagnosed by the patient's physical exam and by immunological tests.
  • Treatment for West Nile virus infections is mainly supportive and is aimed at reducing symptoms; severe infections often require hospital treatment.
  • Risk factors for West Nile virus infections include exposure to infected mosquitoes, being age 50 and older, and having any medical problem that reduces the immune response.
  • In general, the prognosis of most West Nile viral infections is very good; however, severe infections have a more guarded prognosis because of potential neurological damage.
  • Currently, there is no vaccine available to prevent West Nile virus infections in humans; however, preventing mosquito bites by several methods (wearing long-sleeved shirts, long pants, using mosquito repellent, and eliminating areas that are good breeding grounds for mosquitoes) help prevent infections.

West Nile Virus Overview

West Nile virus is a Flaviviridae virus transmitted to humans by mosquito bites. Virus symptoms range from none to severe: encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). The disease the virus causes is termed West Nile encephalitis (WNE). WNE currently is endemic in Asia, Africa, and the Middle East. Since 1999, the disease has been detected in many states (see map below) in the U.S. The disease is considered to be endemic now in the U.S.; in 2013, 39,567 individuals had been diagnosed with the disease. From 2013-2015, about 2,000 per year are detected with new West Nile infections in 47 states in the U.S.

West Nile virus was discovered in 1937 in the West Nile district of Uganda. Although wild birds are the preferred hosts for the virus and are likely the hosts that spread the disease from country to country, West Nile virus can infect other mammals such as horses and dogs, for example. The virus is transferred from animal or birds to humans by mosquitoes. Since the virus was first detected in the United States in 1999, every year since then there has been an outbreak in the U.S. of West Nile virus (for example, outbreaks have occurred in California, Arizona, Illinois, Massachusetts, Oregon, Pennsylvania, Wisconsin, and Texas); the virus has been detected in 47 U.S. states and in Canada.

Medically Reviewed by a Doctor on 4/9/2015

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West Nile Virus Infection Symptoms

The following are the symptoms to be aware of about 3 to 14 days after an infected mosquito bites a person and transmits the West Nile virus:

  • West Nile virus infection typically begins with the abrupt onset of fever, chills, muscle aches, headache, and overall feeling of illness. Headache is particularly common and may be severe. The person may have sensitivity to light with pain behind the eyes.
  • Most people fully recover. In others, particularly the elderly and some young children, the disease can progress to cause encephalitis or meningitis and infrequently, death.

Read What Your Physician is Reading on Medscape

West Nile Encephalitis »

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.

Read More on Medscape Reference »

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