What is West Nile Virus?

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. 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 illness caused by WNV.

Definitions related to West Nile Virus infections in humans:

• Infection refers to both symptomatic and asymptomatic persons with laboratory evidence of recent or current WNV infection.
• West Nile fever is a febrile (fever-causing) illness that is characterized by symptoms include headache, myalgia (pain in one or more muscles), arthralgia (pain in one or more joints), and is sometimes accompanied by a skin rash or lymphadenopathy (abnormal enlargement of the lymph nodes).
• Neuroinvasive disease (affecting the central nervous system) can occur in three forms:
  • Aseptic Meningitis, which is usually characterized by fever, headache, stiff neck and pleocytosis (presence of a greater number of cells than normal) in cerebral-spinal fluid.
  • Myelitis, which is usually characterized by fever and acute limb paresis (slight or partial paralysis) or flaccid paralysis.
  • Encephalitis, which is usually characterized by fever, headache and altered mental status ranging from confusion to coma, with or without additional signs of brain dysfuntion.
• Asymptomatic (without symptoms) infections are defined as blood donors who test positive for WNV during the blood screening of their donation, or asymptomatic persons who are screened and found to have positive antibodies against WNV.
• We are also reporting blood donors with unknown symptomology who were reported to us as having a positive screen for WNV.

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.
• 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.

A pre-recorded multiple-language information line on West Nile Virus can be reached by dialing the Sacramento County Public Health Information Line at 916- 874-2000 or toll free 1-866-319-2001, which is accessible to the 916, 707, 209 and 530 area codes.  Information is recorded in English, Spanish, Cantonese, Vietnamese, Arabic, Hmong, Mien and Russian. 

Please press option number 7 for information concerning West Nile Virus.

Help us track down the West Nile Virus (WNV) 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 also at http://www.westnile.ca.gov/.  

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

If you have any additional questions, regarding West Nile Virus after listening to the information line, please telephone the County of Sacramento, Division of Public Health at 916-875-5881 from 8:00 a.m. to 5:00 p.m. Monday-Friday to reach a live person or you may leave a message after hours.