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West Nile Virus

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Signs and Symptoms

About 80% of those infected with West Nile virus will have no symptoms. About 20% will experience mild to moderate flu-like signs and symptoms that develop between 3 and 14 days after a bite from an infected mosquito. These may include:

  • Fever
  • Nausea, vomiting
  • Headaches
  • Body aches
  • Skin rashes on the chest, stomach and back
  • Swollen lymph nodes

These symptoms may last for a few days or persist for several weeks but have no long-term health impact.

Less than 1% (about 1 in 150) of those infected will develop more serious disease, in which there is central nervous system involvement. This can lead to life-threatening encephalitis and/or meningitis. Signs and symptoms may include:

  • High fever
  • Headache
  • Extreme muscle weakness
  • Neck stiffness
  • Stupor, disorientation
  • Tremors, convulsions
  • Loss of vision
  • Coma
  • Numbness, paralysis (rarely)

These may last several weeks and the effects on the central nervous system may be permanent. The fatality rate of those with the more serious form of the disease is about 10% and is highest among the elderly. Individuals with compromised immune systems or underlying conditions such as diabetes, kidney disease, or high blood pressure also have an increased risk of severe disease.

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