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West Nile Virus


What Is West Nile Virus?

West Nile virus is a virus that can pass to people through the bite of an infected mosquito. The best way to prevent infection with West Nile virus is to prevent mosquito bites.

What Are the Signs & Symptoms of West Nile Virus Infection?

Most of the time, a bite from a mosquito infected with West Nile virus doesn't make a person sick or cause symptoms. When symptoms do happen, they're usually mild and can include:

Rarely, a person can get very ill with problems that affect the central nervous system, such as encephalitis or meningitis. Their symptoms can include:

  • high fever
  • severe headache
  • neck stiffness
  • being confused or disoriented
  • seizures
  • paralysis
  • coma

Severe illness can life-threatening, especially in the elderly and people who are already sick.

How Do People Get West Nile Virus?

Mosquitoes get infected by feeding on birds that carry West Nile virus. They can spread it to people and animals through bites. In the U.S., only one kind of mosquito (out of 175 types) can pass the West Nile virus.

The virus isn't contagious, so it can't spread from person to person.

How Is West Nile Virus Infection Diagnosed?

If someone has symptoms of West Nile virus, doctors consider:

  • whether the person lives in or traveled to an area where infected mosquitoes have been found
  • the season (mosquitoes are more active in warm weather)

The doctor can send a blood sample to a lab to test for the infection.

Someone with symptoms of encephalitis or meningitis may get a lumbar puncture (spinal tap). This test collects some fluid from around the brain and spinal cord for testing in a lab.

How Is West Nile Virus Infection Treated?

Most West Nile virus infections get better on their own. Acetaminophen or ibuprofen can help ease minor aches and pains, and drinking plenty of fluids can prevent dehydration.

Someone with more serious symptoms needs care in a hospital, with IV fluids, breathing help, and other treatments. There is no specific medicine for West Nile encephalitis or meningitis. Antibiotics will not work because a virus, not bacteria, causes West Nile disease. No vaccine for the virus is currently available.

Can West Nile Virus Infection Be Prevented?

The best way to protect yourself and your family from the West Nile virus is to prevent mosquito bites. Be sure to:

  • Use screens on doors and windows, and repair broken or damaged screens right away. Keep unscreened doors and windows shut.
  • Wear long-sleeved shirts, long pants, shoes, and socks when outside.
  • Use insect repellent as directed. Choose one with DEET or picaridin. For kids over 3 years old, you also can use oil of lemon eucalyptus.
  • Limit time outside around dawn and dusk, when mosquitoes are most active.
  • Don't give mosquitoes places to breed. They lay their eggs in water, so get rid of standing water in things like buckets, trash cans, and tires. Empty and clean birdbaths, dog bowls, and flowerpots at least once a week.

What Else Should I Know?

Communities help health officials track West Nile virus infection patterns. If you see a dead bird in your area, do not touch it with your bare hands. Instead, contact your state or local health department to ask what to do with it. If they get a lot of reports of dead birds, they can look to see if they were infected with West Nile virus. If so, health officials can spray the area with pesticides or do other things to help control mosquitoes.

Date reviewed: February 2020