The House Sparrow (Passer domesticus) as a Sentinel for St. Louis Encephalitis Virus

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Abstract
Birds are the primary hosts for St. Louis encephalitis (SLE) virus in most of North America. Because the increased prevalence of antibody in House Sparrows (Passer domesticus) has been related to human cases, this species has been frequently used as a sentinel of SLE virus activity in urban areas. This study investigated the susceptibility of House Sparrows to two strains of SLE virus, measured antibody profiles, and evaluated the use of House Sparrows in an urban surveillance system. House Sparrows were susceptible to both strains of SLE virus inoculated, although not equally, and produced viremias sufficient to infect vector mosquitoes. Both hemagglutination-inhibiting (HI) and neutralizing (N) antibody developed rapidly and to high titers within 2 weeks after inoculation. Detectable humoral antibody began to disappear by 3 months, but persisted for 2 years in 27% for HI and 36% for N antibody of the surviving birds. However, all of the surviving birds were resistant to reinfection with SLE virus at 2 years after inoculation. The titer of HI antibody appeared to be useful in determining recent exposure to SLE virus. The experimental data on HI antibody development and persistence was related to field serologic data from House Sparrows. The monthly prevalences of SLE antibody for independent samples of sera from House Sparrows collected in Memphis, Tennessee, in 1980 were similar. SLE amplification in the House Sparrow population was delayed until September. The Memphis arbovirus surveillance system detected the amplification quickly, and responded with increased adult mosquito control in the focal areas. Urban surveillance of SLE utilizing House Sparrows as sentinels is discussed.