Mosquito-Borne Disease Surveillance
Collecting adult mosquitoes can provide several important pieces of information. When traps are set at specific locations over a period of time, or in response to service requests, increases in the mosquito population can be detected. Once these mosquitoes are identified, control measures can then be more easily directed. Knowing what species of mosquito is breeding can help Vector Control Technicians find the breeding source and take the appropriate control measures. After identification by District Vector Ecologists, these mosquitoes can also be tested for the presence of disease. The detection of virus in a mosquito which feeds on humans indicates a true potential for human disease, and immediate control measures can be implemented. Trap collections not only determine where control measures are needed, but also determine the effectiveness of control measures which are in place.
Several of the 48 known species of mosquitoes in California can carry disease under the right conditions. When a female mosquito takes an animal blood meal, which she uses as nourishment for her developing eggs, she may transmit certain disease causing organisms to humans and other animals. These organisms are taken with blood from other infected humans and animals. The mosquito completes the cycle when she bites the next susceptible host, causing infection. The two most important diseases affecting humans worldwide are encephalitis and malaria.
In Los Angeles County, mosquitoes that are capable of transmitting St. Louis Encephalitis (SLE) and Western Equine Encephalomyelitis (WEE) are pooled and sent to the State Viral and Rickettsial Laboratory for testing.
Currently, the District uses three types of traps to monitor mosquito populations.
New Jersey Light Trap
CDC-Type CO2-Baited Trap
This trap is used to selectively sample host-seeking females attracted to the trap by the sublimation of dry ice into carbon dioxide (CO2) which simulates the exhaled respiratory gases of birds or mammals. The trap consists of a central 3" diameter plastic cylinder housing a 6V DC motor and a 4" fan blade, a collection net attached to the bottom of the cylinder, a 6V battery power source, and an insulated container with 2-5 pounds of dry ice. CDC-type traps utilized by the District also incorporate a mini-light source which help attract mosquitoes as well. Mosquitoes attracted to the trap are drawn in through the top of the trap and forced downward by the fan into the collection net. Live-trapped females can be counted and tested for mosquito-borne arboviruses.
Sentinel Chicken Surveillance
Sentinel chicken serology is performed by placing chickens in an area over an
extended period of time and testing their blood for the presence of antibodies to SLE and WEE
viruses. The District maintains 15 flocks of chickens located strategically
throughout the District.
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