Surveillance is an essential component of an Integrated Vector Management Program, and a considerable amount of our effort is devoted to conducting adult and immature mosquito surveillance. We also conduct surveillance for other vectors such as ticks and yellowjackets. The newest part of our surveillance program is our ability to conduct disease surveillance through on-site testing of mosquito and tick samples. We are also now capable of conducting West Nile virus tests of dead birds.
Our program consists of locating mosquito development sources and monitoring mosquito populations and disease activity over time and space. We collect and analyze data on abundance of larval and adult mosquito species, we monitor distribution patterns of the different mosquito species, determine risk periods of public exposure to mosquito-borne diseases, and evaluate mosquito control activities.
West Nile Virus Surveillance
Mosquitoes are trapped and collected from the field and brought back to the lab where the collected females are pooled together by species. Each pooled sample contains from one to 50 mosquitoes per pool. Each sample is tested for West Nile virus, St. Louis Encephalitis, and Western Equine Encephalomyelitis.
Aside from mosquitoes, we also test dead birds that we collect from reports to the California Dead Bird hotline for the presence of West Nile virus. Typically, dead birds are the first sign that West Nile virus activity is increasing in an area.
We also use sentinel chickens to help us track virus activity. By strategically placing sentinel flocks of chickens at several locations within Placer county, we are able to monitor and track virus activity. Within a few days after being bitten by a mosquito infected with virus, the chickens develop specific antibodies to that virus. They do not become ill or die. Blood samples from the chickens are routinely taken by laboratory staff and sent for testing for the presence of these antibodies. Typically, the chickens are tested every other week during the mosquito season (May until October). If the presence of these antibodies is confirmed by the California Department of Public Health laboratory, there is an increased potential risk that these viruses could be transmitted to wildlife, horses or humans.
During peak tick season (October-April) our staff collects ticks at designated tick surveillance sites. We are able to pool and test these ticks for Lyme disease. This information helps us identify high-risk areas for tick-borne disease based on abundance of ticks and/or presence of disease in the tick population.