West Nile Virus

West Nile Virus is a mosquito-borne infection. Infected mosquitoes can spread the virus to humans and other animals. West Nile Virus is usually spread by the bite of a mosquito that has fed on an infected bird.

Most people who get West Nile Virus experience no symptoms or only mild flu-like symptoms, but it can cause serious illness and there are few medical options to treat or prevent it.

Who is at risk of West Nile Virus?

Anyone can become infected if they are exposed to a mosquito bite. It only takes a single bite from an infected mosquito to contract West Nile Virus.

The risk of West Nile Virus varies from year to year based on precipitation, temperature, and mosquito populations. The highest risk periods are generally when mosquito populations are at their peak during the summer months. Individuals spending time outdoors are greater risk of exposure.

Some people are at greater risk for serious health effects from West Nile virus. This includes:

  • People over the age of 50
  • People with chronic diseases, such as cancer, diabetes, alcoholism or heart disease
  • People who require medical treatment that may weaken their immune system, such as chemotherapy.

What are the symptoms of WNV?

While most people who get WNV (70%-80%) show no symptoms and do not become ill, others may show mild symptoms. Symptoms can range from mild to severe. First symptoms usually appear within 2 to 15 days after infection.

Mild symptoms may include:

  • fever
  • headache
  • mild rash
  • body aches
  • Very few people (fewer than 10% of those with symptoms) have severe symptoms that affect the central nervous system (nerve tissues in the brain and spinal cord)

Severe symptoms may include:

  • very bad headache
  • fever
  • stiff neck (you might have trouble moving your neck side-to-side)
  • nausea or vomiting
  • difficulty swallowing
  • drowsiness
  • blurred vision or worsening eyesight
  • confusion
  • muscle weakness and reduced coordination



There is no specific treatment or vaccine for West Nile virus infection in humans. Health care  Professionals diagnose WNV infection based on: Patients symptoms, geographic location and time of year they were bitten, and the results of laboratory tests. Hospitalization or nursing care may be necessary. Although most people with serious symptoms and health effects fully recover, others can experience long term, ongoing health problems.

These problems may include:

  • Physical effects, muscle weakness, headaches
  • Mental effects, confusion, depression, concentration, memory loss
  • Functional effects, physical activities, routine daily tasks

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