West Nile Virus


West Nile virus (WNV) is an infection from a mosquito. Rarely, it can lead to serious problems, or death.


The infection is caused by a virus. The virus is spread to humans from the bite of an infected mosquito. Rarely it has spread from an infected blood transfusion, organ transplant, and breastfeeding.

Risk Factors

Things that raise the risk of WNV are:

  • Spending time outdoors—in areas with mosquitoes
  • Not using insect repellent
  • Mosquitoes in the home
  • Certain gene defects—that may make some people get infected more easily

Severe WNV is more common in men and people over 50 years old. Other things that raise the risk of severe WNV are:

Mosquito Bite

Mosquito bite
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Most people with WNV have no symptoms. Others develop flu-like symptoms such as:

  • Fever and chills
  • Headache
  • Muscle pain
  • Nausea and vomiting
  • Diarrhea
  • Rash
  • Swollen lymph nodes
  • Eye inflammation— conjunctivitis

Symptoms can last from a few days to several weeks.

A small number of people with WNV develop serious symptoms, such as:

  • Headache and sensitivity to light
  • High fever
  • Stiff neck
  • Confusion
  • Lack of responsiveness or coma
  • Uncontrolled body movements
  • Muscle weakness, or not being able to move


The doctor will ask about your symptoms, travel, and health history. A physical exam will be done.

WNV is often diagnosed with:

  • Blood tests
  • Lumbar puncture— some fluid around the brain and spinal cord is taken and tested

Other tests may be done, depending on symptoms.


There is no specific treatment for WNV. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. In severe cases, hospital care is needed.

Depending on the symptoms, options may be:

  • Pain medicines
  • Medicine to ease nausea and vomiting
  • Fluids by mouth or IV—to treat dehydration

Treatment for severe symptoms may include:


WMV can be prevented by avoiding mosquito bites. Things that may help are:

  • Covering up the skin
  • Using bug sprays, netting, and screens
  • Staying inside between dusk and dark


Centers for Disease Control and Prevention
Infectious Diseases Society of America


Alberta Ministry of Health


Mosquito avoidance. EBSCO DynaMed website. Available at: https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 5, 2021.
Sejvar JJ. West nile virus infection. Microbiol Spectr. 2016;4(3).
West Nile virus infection. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/west-nile-virus-infection . Accessed April 5, 2021.
West Nile virus: What you need to know. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/westnile/index.html. Accessed April 5, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP

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