West Nile Virus Information

West Nile Virus (WNV) is one of a group of disease-causing viruses spread by mosquitoes. It first appeared in the United States in 1999.  The virus is transmitted to humans and animals through the bite of an infected mosquito.  Mosquitoes become infected with WNV when they feed on infected birds.

Most people who are bitten by a mosquito with WNV will not get sick.  People who do become ill may experience flu-like symptoms such as a fever, headache and body ache but the virus can also cause severe illness and even death.

Approximately one in five people bitten by an infected mosquito will become ill.  Less than one percent of infected individuals require hospitalization.  The elderly and the immune-compromised are most susceptible to severe illness caused by WNV.

Definitions related to West Nile Virus infections in humans:

  • Infection refers to both persons who have laboratory evidence of recent or current WNV infection regardless of whether or not they have symptoms.
  • West Nile fever is an illness with fever and a variety of symptoms, including headache, muscle and joint pain, and sometimes a skin rash or enlarged lymph nodes. The illness may go away in a few days or could last for several weeks.
  • Neuroinvasive disease (affecting the central nervous system) can occur in three forms:
    1. Aseptic Meningitis, which is an inflammation of the membranes covering the brain.  Symptoms include fever, headache, stiff neck and abnormal white blood cells when the spinal fluid is tested
    2. Myelitis, which results in paralysis of one or more limbs
    3. Encephalitis, which means swelling of the brain. Symptoms include fever, headache and altered mental status ranging from confusion to coma.

Severe West Nile Virus disease can result in death.

To reduce the risk of being bitten by mosquitoes and contracting WNV, residents are urged to follow Sacramento-Yolo Mosquito and Vector Control District's 7D’s of protection:

  • DEFEND yourself against mosquitoes by using an effective repellant, such as DEET, Picaridin or Oil of Lemon of Eucalyptus. Make sure you follow label directions
  • DRAIN all sources of standing water that may support mosquito breeding habitats
  • DOOR and window screens should be in good working condition. This will prevent mosquitoes from entering your home
  • Moquito Vector Control DISTRICT personnel are on hand to help address any mosquito problem you may be experiencing
  • DAWN and DUSK are times to avoid. This is the time when mosquitoes are most active
  • DRESS appropriately by wearing long sleeves and pants when outdoors.

Help us track down the West Nile Virus  by reporting all dead birds and squirrels. Telephone 1-877-968-2473 toll-free to report a dead bird or squirrel. You can also submit an online report at www.westnile.ca.gov/report_wnv.php

Further information about the latest West Nile Virus activity throughout California, and by individual County, can be found  at http://www.westnile.ca.gov/

If you have questions specifically concerning mosquitoes please telephone Sacramento-Yolo Mosquito and Vector Control District at 916-685-1022.

Quick Links

West Nile Virus Advisory May 2011
A reminder that West Nile Virus is endemic to Sacramento County and that laboratory testing for the disease begins each May.
West Nile Virus Links, Maps & Information

Connect with Sacramento County
Sign-up for news updates!
Translation Disclaimer