West Nile Virus

Last Updated: July 31, 2018

​West Nile Virus (WNV) is a flavivirus that can infect humans, birds, mosquitoes, horses, and other mammals. The main route of transmission is through the bite of an infected mosquito. The virus can also be transmitted through blood transfusions, organ transplants, breastfeeding, and during pregnancy from mother to baby. The virus is not spread through direct contact with an infected person.


Clinical Symptoms

When someone has been infected with West Nile Virus they will typically have one of three outcomes:

      No Symptoms: Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.

      Milder Symptoms: Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches.

      Serious Symptoms: About one in 150 people infected with WNV will develop severe, neuroinvasive illness. The symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.


There is no vaccine or specific treatment for WNV infection. In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive therapy.


The easiest and best way to avoid WNV is to prevent mosquito breeding sites and bites.

  • Eliminate mosquito breeding sites by removing and emptying sources of standing water.
  • Apply EPA registered insect repellent to exposed skin.
  • Spray clothing and supplies with permethrin, and utilize permethrin treated bed net, if applicable.
  • Ensure windows and doors have screens and are sealed tight.
  • Cover up-the more clothes you have on, the fewer bites you'll get.Mosquitos Suck poster



West Nile Virus Fact Sheet

Information Products on Mosquito-Borne Diseases and Control

Army Vector-borne Disease Report

External LinkCDC WNV Activity Map



Seek medical attention if you think you have been exposed to WNV and develop a high fever with severe headache.