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West Nile Virus (cont.)

West Nile Virus and West Nile Encephalitis Risk Factors

The major risk factor for West Nile virus and West Nile encephalitis is being exposed to mosquitoes that may be carrying the virus. Such individuals are those who spend time outdoors and have skin exposed for mosquitoes to bite (for example, campers, hikers, those engaged in outdoor working conditions). Individuals who are is 50 years of age or older and individuals who have a weakened immune systems (cancer patients, diabetics, for example) are at higher risk for both infection and encephalitis.

West Nile Virus and West Nile Encephalitis Symptoms and Signs

Signs and symptoms of the West Nile virus infection range from no symptoms at all to a rapidly fatal brain infection. The incubation period ranges from two to 14 days although two to six days is the most common range. In areas where the virus is common, people are more likely to show no symptoms of the infection or have only a mild, flu-like illness rather than a severe brain infection. The following describes symptoms and their frequency of occurrence:

  • According to the CDC, the majority of people (70%-80%) who become infected show no symptoms and recover completely.
  • When symptoms develop, West Nile virus infection typically begins with the abrupt onset of fever, chills, muscle aches, headache, and flu-like symptoms. Headache is particularly common and may be severe. The person may have sensitivity to light with pain behind the eyes, and some patients may also develop vomiting, diarrhea, or a rash. Although fatigue and weakness may last for weeks or even months, most patients recover completely. The set of symptoms described here may occur in about 20% of infected patients.
  • In others, particularly the elderly, the disease can progress to cause encephalitis or meningitis. These patients may show neurological changes such as disorientation, tremors, seizures, and develop other symptoms such as headache, high fever, and neck stiffness. Some of the neurological effects will become permanent, and about 10% of people who develop severe neurological infections will die. People with certain medical conditions (cancer, diabetes, hypertension, and kidney disease) are at higher risk for serious West Nile virus infections.
Medically Reviewed by a Doctor on 4/9/2015

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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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