What We Do
WNV exhibits similar ecological requirements as other North American mosquito transmitted arboviruses, such as St. Louis encephalitis (SLE) virus. Studies of the SLE virus vectors and reservoir hosts observed during the SLE outbreak (26 reported human cases) in southern California in 1984 have provided information that can be applied to the WNV cycle when it enters southern California.
The District's experience with SLE has demonstrated that mosquitoes capable of transmitting virus develop readily in 1) residential back yards (e.g., sprinkler filled containers and runoff) and in 2) surface drainage found in curb gutters, catch basins, underground drains, and storm channels. The Orange County Vector Control District (District) controls mosquito breeding in the latter accessible public areas throughout Orange County (OC). However, the District cannot adequately control mosquito production in water holding containers in the more than 730,000 individual back yards in Orange County. The extent to which WNV transmission occurs in OC will depend largely on the degree to which citizens respond to backyard mosquito control advisories from the District's Communications Department, the effectiveness of mosquito (larva) control around identified WNV activity foci, and the success of the underground catch basin and manhole chamber mosquito control program.
What is the California West Nile Surveillance Program?
The first human case of WNV was confirmed in California in September 2002. The California Department of Health Services (DHS) has overseen a statewide mosquito-borne encephalitis virus surveillance program since 1969 for western equine encephalitis (WEE), St. Louis encephalitis (SLE), and other viruses. In 2000, DHS, the District, and other agencies expanded their programs to enhance the ability to detect WNV. A protocol to report and test dead birds has been added to the existing encephalitis case surveillance system, that also includes mosquito testing and monitoring of sentinel chickens.
Encephalitis Case Surveillance
DHS tracks cases of human, horse, and ratite (e.g., emu, ostrich) encephalitis. The routine testing of encephalitis cases for WNV will assist in the early detection of the virus in California. Human and animal encephalitis cases are also routinely tested for WEE and SLE viruses.
Mosquitoes throughout the state are sampled for the presence of WEE, SLE, and now WN viruses. Local mosquito and vector control agencies also monitor the abundance and type of vector mosquitoes.
Sentinel Chicken Testing
Approximately 200 chicken flocks are strategically placed throughout the state and are tested routinely during the mosquito season to detect evidence of infection from WN, WEE, or SLE viruses.
Small Bird Surveillance
The District and a number of other vector control districts in the state also conduct SLE, WEE, and WNV surveillance using small birds (e.g., house sparrows, house finches) as indicators of virus transmission. Based upon studies of the SLE virus transmission cycle (SLE is another flavivirus, closely related to WNV) established flavivirus enzootic cycles are maintained in discrete small bird/mosquito interactions. Virus enzootic cycles must become well developed before non-reservoir animals (e.g., crows, humans, horses) become infected when they inadvertently contact the virus/mosquito/small bird cycle. By tapping into an enzootic cycle (e.g., mosquito sampling, small reservoir bird bleeding), detection of virus activity (i.e., virus or antibodies) provides the earliest possible awareness of its presence.Dead Bird Surveillance
California began to test dead crows and related birds for WNV in 2000. Now that the virus has been reported in California, monitoring dead crows and other corvids will help identify other virus foci. State agencies, private organizations, and individuals participate in the surveillance program by reporting dead bird sightings. The District arranges for collection, assessment, and testing for WNV at the District laboratory.
What Do I Do if I See a Dead Bird?
Please call the District to report a dead bird.
You can obtain our contact information by clicking here.
The District WNV Defense Program
Since 1947 the District has provided an effective county-wide mosquito control program to eliminate pest and pathogen carrying mosquitoes. The mosquito control program, still in operation, consists of spraying accessible mosquito sources (e.g., manhole chambers, street gutters, catch basins, flood control channels) with environmentally safe pesticides. Mosquito control of backyard sources (approx. 40% of all mosquito production sites) is accomplished through public awareness announcements to the property owners of Orange County by pamphlets, television, radio, and newspaper.