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West Nile Virus Questions Answered

WebMD has answers to some common questions about West Nile virus.

1. How do people get infected with West Nile virus (WNV)?

People get West Nile virus from the bite of a mosquito that has fed on an infected bird. Mosquitoes can't transmit the virus from one person to another.

It's also possible to get West Nile virus from a blood transfusion or an organ transplant from an infected donor. Since all blood donated in the U.S. is tested for the virus, the blood supply in this country is considered safe.

2. What are the symptoms of West Nile virus infection?

Four out of five people infected with West Nile virus don't have any symptoms. A few of these people may develop lingering infections that might cause problems years later. But most will become immune to the virus and never get a West Nile illness.

One in five infections results in West Nile fever. Once considered a relatively mild illness, the CDC now says people with West Nile fever can be quite ill for quite a long time.

The symptoms of West Nile fever include:

In one in every 150 infections, the virus gets into the brain (encephalitis) or into the tissues covering the brain and spinal cord (meningitis). This is what the CDC calls "neuroinvasive" West Nile disease.

About 10% of people who get West Nile encephalitis or West Nile meningitis die. Most people with neuroinvasive disease have either encephalitis or both encephalitis and meningitis. Some 25% to 35% get meningitis only.

The symptoms of West Nile meningitis include:

The symptoms of West Nile encephalitis include:

  • Changes in consciousness ranging from mild (sluggishness) to severe (mental confusion, convulsions, or coma).
  • Fever and headache.
  • Neurological symptoms, including paralysis of one or more limbs or palsy, may occur.
  • Tremors and movement problems sometimes occur.

Some people with West Nile infection become weak or paralyzed in one or more limbs. Two-thirds of these people are left with permanent weakness or paralysis. It's not yet clear what percentage of people with neuroinvasive West Nile disease get this syndrome, known as West Nile poliomyelitis.

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