West Nile Virus



The infection is caused by a virus that 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
  • Faulty genes that may make some people get infected more easily

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

Mosquito Bite
Mosquito bite
Copyright © Nucleus Medical Media, Inc.



Most people with WNV do not have 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 symptoms and past health. Questions may also be asked about any recent travel. A physical exam will be done.

WNV is often diagnosed by looking for signs of infection with:

  • Blood tests
  • Lumbar puncture— removes a sample of fluid around the brain and spine

Other tests may be done depending on a person's symptoms.



There is no specific treatment for WNV. The goal is to manage symptoms. People with severe symptoms may need hospital care.

Options are:

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

Treatment for severe symptoms may include:

  • Mechanical ventilation to help with breathing
  • Medicine to control seizures
  • Medicine to ease brain swelling


The risk of WMV may be lowered 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

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.