2011 Annual Report - Sacramento-Yolo Mosquito & Vector Control ...

SurveillanceWild BirdsThe District’s wild bird surveillance program monitors the presence of antibody for encephalitisvirus in the avian population in rural and suburban habitats. The purpose of the program isto aid in the identification of local enzootic virus transmission, the determination of avianhosts, their residency, mobility, longevity, and mortality by maintaining records of changesin abundance, age structure, and immunity. Data provided by this program contribute to ourunderstanding of the local infection cycle in birds and mosquitoes, and assist in the assessmentof the risk of virus transmission to residents. The program was initiated in the spring of 1996to monitor the endemic Western Equine Encephalomyelitis virus and has since also providedthe first evidence of West Nile Virus transmission in Sacramento County and tracked the virusas it rapidly moved into the resident bird population and became established.In order to capture wild birds, the District uses mist nets and seed-baited traps with authorizationfrom the U.S. Geological Survey, Bird Banding Laboratory in Laurel MD, and the CaliforniaDepartment of Fish and Game. Each captured bird is aged, sexed, weighed, measured,banded, and a small blood sample (0.1ml/10g wt.) is collected to test for the presence ofarbovirus antibody. Birds are released at the location of capture and samples are broughtinto the District’s laboratory, where they are tested by an enzyme-linked immunosorbent assay(ELISA) that identifies antibody to the different viruses.The use of wild birds as an arbovirus surveillance tool has provided a serological history ofWNV in our District. The wild bird surveillance program is maintained through a cooperativeagreement and with volunteer personnel support from the US Fish and Wildlife Service on theStone Lakes National Wildlife Refuge. In 2011, a total of 711 blood samples were tested from54 bird species. The collected sera were tested for antibody to Western EncephalomyelitisVirus (WEEV), St. Louis Encephalitis Virus (SLEV), and West Nile Virus (WNV). Only antibodyfor WNV was detected in birds sampled in 2011. Overall, WNV antibody was detected in0.8% of the samples.WNV Seropositive Wild Birds in 2011BirdPositive detections (total sampled)Western scrub-jay 1 (5)Snowy egret 1 (6)Great-tailed grackle 1 (2)Song sparrow 1 (108)Green heron 1 (6)Birds are released at the location of capture andsamples are brought into the District’s laboratory.2011 Annual Report11