Besides being a nuisance by disrupting human activities, certain insects and animals may transmit a number of diseases. hose of most concern in the San Gabriel Valley are St. Louis encephalitis (SLE) and Western equine encephalomyelitis (WEE) transmitted by mosquitoes, plague and murine typhus transmitted by fleas, hantavirus pulmonary syndrome and arenaviruses transmitted through the excretions of rats and mice, and Lyme disease transmitted by ticks.
The District utilizes various methods for the surveillance of mosquito
transmitted disease. Samples are tested for the presence of antibodies to SLE, WEE, and WN viruses.
Adult Mosquito Pools are routinely collected using carbon
dioxide-light traps designed to attract host seeking female
mosquitoes. Trap counts of 50 or more per species allow for
laboratory testing to determine if the mosquitoes are infected.
Sentinel Chicken Flocks are strategically placed and maintained throughout the District. These chickens serve as sentinels or preemptive warning signals for the presence of encephalitis virus activity in the environment. The mosquitoes most responsible for SLE and WEE transmission (Culex tarsalis, and
Culex pipiens) prefer to feed on birds, thus sentinel chickens will routinely show virus activity prior to disease outbreaks in humans. Small blood samples are taken every 10-14 days and tested in our laboratory for antibodies to these viruses.
Wild Bird Traps located near chicken coops provide our District with
additional sentinel capabilities. Sparrows and finches enter these traps for food and water, and after a small sample of blood is retrieved, they are
released. These samples are tested as well for virus antibodies.
Other Vector-borne Diseases:
Plague and murine typhus are flea transmitted diseases.
Hantaviruses and arenaviruses are transmitted through rodent feces and urine. These are all endemic in the wild animal populations of southern California. Routine surveillance is necessary to monitor disease potentials and rodent population trends. Increases in human-rodent interactions caused by drought, unsanitary conditions, and urban sprawl into foothill habitats triggers a heightened concern for disease transmission potentials. Rodents, and their ectoparasites such as fleas and ticks are routinely trapped and tested for the presence of disease.