What is West Nile virus?

West Nile virus is an infection spread to humans by mosquitoes. Most people who get the virus don't get sick. But when symptoms do occur, they appear 2 to 14 days after the bite and include fever, headache, body aches, and sometimes a skin rash. It's usually a mild illness.

Most people fully recover from West Nile. People older than 55 and those with immune system problems are at the highest risk for serious problems from West Nile. In rare cases, West Nile virus may affect the brain, causing serious illness that can lead to long-lasting problems.

How is it spread?

Most often, mosquitoes spread the virus by biting birds infected with the virus and then biting people.

Mosquitoes can also spread the virus to other animals, such as horses. But you can't get West Nile from these other animals. And you can't get it from touching or kissing an infected person.

What are the symptoms?

Most people who have West Nile have no symptoms.

When symptoms do appear, they start 2 to 14 days after the mosquito bite.

Mild symptoms may include:

• Fever. This may last for about 5 days.
• Headache. This may last for about a week.
• Feeling very tired. This may last for a few weeks.
• Feeling less hungry than usual.
• Body aches.
• A rash, usually on the chest, and swollen lymph nodes.

If you have a more severe case of West Nile, symptoms can last for weeks or months. Symptoms may include:

• A severe headache.
• High fever.
• Stiff neck.
• Confusion or reduced attention to surroundings.
• Tremors or convulsions.
• Muscle weakness or paralysis.
• Coma.

When symptoms are most severe, it can lead to swelling of the brain (encephalitis), the spinal cord (myelitis), or the tissues around the brain and spinal cord (meningitis). You may need to stay in the hospital so you can get medicine and treatments for your specific symptoms to help you recover.

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

How is it diagnosed?

If your doctor thinks that you may have West Nile, they 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 swelling of the brain (encephalitis).

How is West Nile treated?

There is no specific treatment for West Nile. 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.

If you have severe West Nile, you may need to stay in a hospital so you can get treatment to help you recover. You may get fluids given through a vein (intravenous, or I.V.) and treatments to prevent other infections, such as pneumonia. You also may be given medicine to help with pain or fever.

How can you help prevent it?

There is no vaccine to prevent West Nile virus. But you can do things to help protect yourself from mosquito bites, especially when you travel.

• Wear long pants and long-sleeved shirts. Some outdoor-clothing stores sell clothing already treated with insect repellent.
• Use insect repellents recommended by the Environmental Protection Agency (EPA).
  • Use one with DEET, picaridin, IR3535, oil of lemon eucalyptus, paramenthane-diol, or 2-undecanone. You can get repellents in different strengths. Read and follow all instructions on the label, especially for how to use them on children.
  • Spray clothing with DEET. Mosquitoes may bite through thin clothing. (Remember that DEET can damage plastic, such as watch crystals, eyeglass frames, and some synthetic fabrics.)
• Sleep under bed nets (mosquito netting).
• Use flying-insect spray indoors around sleeping areas.
• Do not leave puddles or open containers of water near your house. Mosquitoes breed in standing water.
• Stay indoors at dawn, at dusk, and in the early evening when mosquitoes are the most active.

To learn more

The most current information about West Nile is available from the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). You can learn about the risk of West Nile in the area you're traveling to by:

• Visiting the CDC website at www.cdc.gov/westnile or by calling their toll-free phone number (1-800-232-4636).
• Contacting your doctor or local health department.