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West Nile Virus Infection

Medically reviewed by Last updated on Oct 31, 2022.

What is West Nile virus (WNV) infection?

WNV is carried by mosquitoes. The virus spreads to humans when they are bitten by infected mosquitoes. An infected mother who is pregnant or breastfeeding may pass the virus to her child.

What increases the risk of WNV infection?

People who travel to places where WNV is common have a higher risk of infection. Those staying or working outdoors may have an increased risk for the infection. Some factors may cause a mild WNV infection to develop into the more severe form of the disease. You may be at increased risk for a more severe form of the disease if:

  • You are older than 70 years.
  • You have a long-term condition that weakens your immune system, such as diabetes, cancer, or AIDS.
  • You take medicine that weakens your immune system, such as steroids, chemotherapy, or antirejection medicine.

What are the signs and symptoms of WNV infection?

Most people who have WNV never know they are infected. You may have flu-like symptoms such as fever, headache, eye pain, muscle pain, fatigue, runny nose, cough, and sore throat. You may have loss of appetite, nausea, vomiting, abdominal pain, or diarrhea. A red skin rash may develop. The severe form of WNV infection may include fever with one or more of the following:

  • Severe headache, stiff neck, or neck pain
  • Confusion or changes in behavior
  • Severe fatigue or sleepiness
  • Seizures, uncontrolled shaking, jerking, stiffness, or slow movement

How is WNV infection diagnosed?

Your healthcare provider will ask you for a detailed health history. This includes information about your past travels or activities, exposures and contacts, or diseases you may have had. You may need one or more of the following tests:

  • Blood samples may be tested for WNV infection.
  • CT scan or MRI pictures may show inflammation in your brain. You may be given contrast liquid to help your brain show up better in the pictures. Tell the healthcare provider if you have ever had an allergic reaction to contrast liquid. Do not enter the MRI room with anything metal. Metal can cause serious injury. Tell healthcare providers if you have any metal in or on your body.
  • A lumbar puncture, or spinal tap, may be used to A needle is inserted into your spinal canal through your back. Healthcare providers will collect a sample of spinal fluid and send it to a lab for test for signs of infection.
  • An EEG prints a paper tracing of brain wave activity from different parts of your brain. Healthcare providers look at the tracing to see how your brain is working.

How is WNV infection treated?

No medicine is available to treat WNV. If you develop severe signs and symptoms of WNV infection, you may need to stay in the hospital. You may have one or more of the following to relieve your signs and symptoms:

  • Breathing support may include oxygen or a respirator to help you breathe.
  • IV fluids may help prevent or treat dehydration.
  • Medicines may be needed to decrease pain, headaches, and fever, or to control seizures. Healthcare providers may also give you medicine to decrease swelling and pressure within your head. Antibiotic medicine may be given if you have a bacterial infection in addition to your WNV infection.

How can I manage my symptoms?

  • Rest as needed. Start to do more each day as you feel better.
  • Drink liquids as directed. Ask how much liquid to drink each day and which liquids are best for you.
  • Rehabilitation may be recommended after you recover. You may need physical, occupational, or speech therapy. These may help to improve movement, decrease pain, maintain daily activities, and improve your ability to eat or speak.

How can a WNV infection be prevented?

  • Avoid mosquito bites:
    • Use an insect repellant that contains the active ingredient DEET on your clothing and exposed skin. Ask about other insect repellants to prevent bites. Use repellants with 30% DEET or less on infants younger than 2 months. Follow the instructions on the label when you use an insect repellant. Do not use DEET on the hands of young children or on babies who may rub their eyes or mouth.
    • Do not go outside at sunrise and sunset, when mosquitoes are most active. If you sleep outdoors, use a mosquito net.
    • Put screens on all windows and outside doors of your house. Repair screens that have holes in them.
    • Wear long-sleeved shirts and long pants to keep your skin covered.
  • Control mosquito breeding: Get rid of places where water can stand and mosquitoes can live.
    • Do not leave containers that can collect water, such as buckets or wheelbarrows, in an uncovered or upright position.
    • Change water in animal feeders every few days.
    • Regularly check ponds, birdbaths, animal feeders, drinking troughs, and other bodies of standing water.
    • Drain or pump out standing water around your house, such as in clogged gutters and ditches.

Where can I find more information?

  • Centers for Disease Control and Prevention (CDC)
    1600 Clifton Road
    Atlanta , GA 30333
    Phone: 1- 800 - 232-4636
    Web Address:

Call your local emergency number (911 in the US) or have someone call if:

  • You become confused, act differently than usual, or become harder to wake than usual.
  • You have shortness of breath.

When should I seek immediate care?

  • Your symptoms get worse or come back.
  • You have a severe headache, stiff neck, or trouble thinking clearly.
  • You have a seizure.
  • You have weakness or cannot move a part of your body.
  • You have difficulty swallowing or speaking, or you have double vision.

When should I call my doctor?

  • You have a fever.
  • Your skin is itchy, swollen, or has a rash.
  • Your symptoms do not improve with treatment.
  • You have questions or concerns about your condition or care.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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