West Nile Virus

2017 Reported West Nile Virus Infections in Orange County (Infections by Type)
(as of 11/22/2017)


Age Group

Disease Type





18 - 49

50 - 64

≥ 65

West Nile Neuroinvasive Disease








West Nile Fever
















Classification Pending








Total Infections








Total Deaths



What is West Nile Virus?

A. West Nile virus (WNV) is a virus that is most commonly spread by the bite of an infected mosquito. It affects the central nervous system and can cause a potentially serious illness with varying symptoms as described below (What are the symptoms of West Nile Virus infection?). People who spend a lot of time outdoors are more likely to be bitten by an infected mosquito, and people older than 50 years of age are at increased risk for severe disease if bitten by an infected mosquito. In a very small number of cases, WNV was spread through blood transfusions, organ transplantations, from mother-to-baby (during pregnancy and through breastfeeding), and through work exposures (animal handling or laboratory). Animals can also be infected with WNV and certain birds in particular play an important part in the life cycle and spread of the virus although birds do not directly spread the infection to humans. There is no treatment except supportive care for WNV infection, although experimental therapies are currently being studied. Avoiding mosquito bites is the #1 way to prevent WNV infection.

WNV was first seen in the United States in New York in August 1999 and has since spread south and westward, with WNV activity reported in all 48 states in the Continental United States.

What are the symptoms of West Nile Virus Infection?

A. West Nile Virus infection is uncommon, even in areas with infected mosquitoes and animals. Infection occurs in less than 1% of people bitten by an infected mosquito. If infection occurs, symptoms begin 2-14 days after the mosquito bite and include:

  • No Symptoms in Most People. Approximately 80 percent of people who are infected with WNV will not show any symptoms at all.
  • Mild to Moderate Symptoms in Some People. Up to 20 percent of the people who become infected will display symptoms, which may include fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms typically last a few days and it is not necessary to seek medical attention unless there is no improvement, more serious symptoms develop, or you are pregnant or breastfeeding.
  • Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and some neurological effects may be permanent.

Protect Yourself

  1. Avoid Mosquito Bites
    1. Apply insect repellent containing DEET (N,N-diethyl-metatoluamide), picaridin, oil of lemon eucalyptus, or IR3535 (3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester) to exposed skin whenever you go outdoors. Be sure to follow the product directions for use.
    2. Wear long-sleeves, long pants and socks when outdoors, whenever possible. Spray thin clothes with repellant to provide extra protection but do not spray repellants containing permethrin directly on the skin and do not spray DEET under the clothing.
    3. Avoid outdoor activities from dusk to dawn, which are peak mosquito biting times. If you must go outdoors in the evening and early morning, be sure to use repellant and protective clothing as described above.
  2. Mosquito-Proof Your Home
    1. Drain standing water (which serve as mosquito breeding sites) around your home. This includes empty containers, flowerpots, bird baths, and pet dishes.
    2. Install or repair tight fitting screens on your windows and doors to keep the mosquitoes out.

  3. Help Your Community
    1. Arrange or participate in neighborhood clean-up days to pick up empty containers, tires, and other standing water sources to eliminate mosquito-breeding sites in your community.
    2. Report dead birds (if they have been dead less than 24 hours) to Orange County Vector Control (714) 971-2421 or to the State of California 1-877-WNV-BIRD. Some birds may be tested for WNV infection. Dead birds may indicate that WNV is circulating in the area.

Mosquito Control

Information on mosquito control is available on the Orange County Vector Control District's Web site at www.ocvcd.org/.

Reporting Dead Birds

The reporting of dead birds can provide important information about WNV activity and is part of the overall WNV surveillance process.

Dead Bird Disposal Options:

  • Orange County Vector Control District (OCVCD) may be able to collect dead birds if suitable for West Nile Virus testing. If a dead bird is found and it appears to have died within the last 24 hours and is in good condition, carefully and without touching the bird, place the carcass in a plastic bag by inverting the bag over it, and put in a cool or shady place, then thoroughly wash your hands and contact OCVCD at 714-971-2421 x117.
  • If you find a dead bird and wish to dispose of it yourself, carefully and without touching the bird, place the carcass in a plastic bag by inverting the bag over it, tie the bag, and dispose of the carcass in your trash container, do not place the bird in your green waste or recyclable materials container, then thoroughly wash your hands.
  • Though disposal of dead animals is very unlikely to transmit West Nile Virus, proper handling of the carcass and hand washing is recommended to minimize the possibility of transmitting of other diseases.
  • If a citizen is uncomfortable with disposing of the bird, contact your local animal care services provider who under certain circumstances may dispose of the bird.

Between 7:00 am and 4:30 pm on Monday through Thursday, or 7:00 am and 3:30 pm on Friday, please contact Orange County Vector Control District at (714) 971-2421 extension 117 or wnsurv@ocvcd.org. Please be aware that there is a limit to the number of birds that Vector Control can test, especially from areas in which WNV has already been detected. In some cases, you may be asked to dispose of the bird carcass.

After regular business hours or on weekends, you may also report dead birds through the Internet to www.westnile.ca.gov/ or call (877) WNV-BIRD.

For more information on West Nile Virus, see: www.cdc.gov/ncidod/dvbid/westnile/index.htm

Latest News

August 18, 2017
Reports of West Nile Virus Infections are Increasing in Orange County

July 7, 2017
First West Nile Virus Infection Identified in Orange County

Safety of Pesticides Used to Control Adult Mosquitoes

Provider Information

West Nile Virus Case Information

For bird information, see www.ocvcd.org/

For current information about the extent of WNV in the United States, please click on this link:

WNV Internet Resources