West Nile Virus


WNV transmission cycle 2

IMPORTANT: For the most up to date information about West Nile virus, including frequently asked questions, visit the State of Oregon's website.

What is West Nile virus?

West Nile virus (WNV) is a potentially serious illness that can attack the nervous system of animals and humans. The virus interferes with normal central nervous system functioning and causes inflammation of brain tissue.

How does West Nile virus spread?

WNV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV when they bite humans or animals.

What are the symptoms?

  • About 80% of people who are infected with WNV will not display any symptoms. 
  • About 20% of people who become infected with WNV have mild symptoms such as fever, headache, body aches, nausea, vomiting and possibly swollen lymph glands or a skin rash. Symptoms can last a few days or several weeks.
  • Less than 1% (1 out of 150 people) infected with WNV will develop severe illness. Symptoms include high fever, headache, neck stiffness, disorientation, convulsions, muscle weakness, vision loss, stupor and numbness. In rare cases, WNV can lead to paralysis, coma or death.

Information about WNV Activity in Oregon