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West Nile Virus

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Topic Overview


What are the symptoms?

About 80 out of 100 people who have West Nile have no symptoms.1 When symptoms do appear, they start 2 to 15 days after the mosquito bite. Mild symptoms may include:

Most people who have the mild form of West Nile have a fever for 5 days, have a headache for 10 days, and feel tired for more than a month.

West Nile causes serious illness in about 1 out of 150 people who get infected.1 It can lead to swelling of the brain (encephalitis), the spinal cord (myelitis), or the tissues around the brain and spinal cord (meningitis). Symptoms of these diseases may include:

Call your doctor right away if you or someone you know has symptoms like these.

If you have a severe case of West Nile, symptoms can last for weeks or months, especially if the infection has spread to your brain.

How is West Nile infection diagnosed?

If your doctor thinks that you may have West Nile, he or she will ask questions to find out when you were bitten by a mosquito and what symptoms you have.

The doctor may also test your blood for antibodies to the virus. The antibodies can show if you have had a recent West Nile infection. The antibodies don't always appear right away, so your doctor may test your blood again in a couple of weeks.

You may also have other tests, such as:

  • A spinal tap (lumbar puncture) to look for antibodies or other signs of the virus in the fluid that surrounds your brain and spinal cord.
  • An MRI scan, which makes pictures of your brain. This scan is done to find out if you have encephalitis.

How is it treated?

There is no treatment for West Nile. Your body just has to fight the infection on its own. If you have a mild case, you can recover at home. Be sure to drink enough fluids and get lots of rest. You may also want to take medicine to reduce pain or fever. You may feel well enough to keep doing your normal activities. Ask your doctor if you need to stay home.

If you have severe West Nile, you may need to stay in a hospital so you can get treatment to help your body fight the illness. You may get fluids given through a vein (intravenous, or IV) and get help preventing other illnesses such as pneumonia. If you have severe trouble breathing, a machine called a ventilator may be used to help you breathe. You also may be given medicine to help with pain or fever.


WebMD Medical Reference from Healthwise

Last Updated: November 14, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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