West Nile Virus

What is West Nile Virus (WNV)?

WNV is a mosquito-borne disease that was originally found in Africa and first detected in the United States in 1999. WNV arrived in California in 2003 and has become an established disease in Sacramento County.

How Does WNV Spread?

WNV most commonly spreads through the bite of an infected mosquito. Mosquitoes become infected when feeding on infected birds. These infected mosquitoes then bite humans and other animals and spread the disease.

The main species of mosquitoes that spread WNV are mosquitoes in the Culex genus. Culex mosquitoes are widespread in California. They tend to bite in the mornings and evenings and feed on birds, humans, and other animals. Culex mosquitoes are not known to spread Zika, dengue, or chikungunya viruses.

What Are the Symptoms of WNV?

No symptoms. Approximately 80% of people who are infected with WNV do not develop any symptoms.

Mild symptoms. Up to 20% of people who are infected with WNV develop symptoms, such as fever, headache, body ache, joint pain, vomiting, diarrhea, and/or rash. Symptoms can last for as short as a few days to as long as several weeks.

Serious symptoms. About 1 in 150 people infected with WNV develop severe symptoms, including high fever, headache, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and/or paralysis. These symptoms can last for several weeks but neurological effects may be permanent. WNV can also be fatal.

How is WNV Treated?

There is no specific treatment for WNV. Mild symptoms usually pass on their own. However those experiencing severe symptoms should seek medical attention to receive supportive treatment, including intravenous fluids, help with breathing, and nursing care.

How Can I Reduce the Risk of Being Infected with WNV?

Practice the Sacramento-Yolo Mosquito and Vector Control District's 7 D's of protection:

  • DRAIN any standing water that may produce mosquitoes.
  • DAWN and DUSK are the times to avoid being outside. This is when mosquitoes are most active.
  • DRESS appropriately by wearing long sleeves and pants when outdoors.
  • DEFEND yourself against mosquitoes by using an effective insect repellant, such as DEET, Picaridin, or Oil of Lemon Eucalyptus. Make sure you  follow label directions!
  • DOOR and window screens should be in good working condition. This will prevent mosquitoes from entering your home.
  • DISTRICT personnel are available to address any mosquito problem you may be experiencing by calling 1-800-429-1022.

Report dead birds that have been dead for less than 24 hours, particularly crows and magpies, to help track WNV activity. You can report by phone by calling 1-877-968-2473 or online by visiting http://westnile.ca.gov/report_wnv.php.