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Host Selection by Culex pipiens Mosquitoes and West Nile Virus Amplification

Gabriel L. HamerDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Uriel D. KitronDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Tony L. GoldbergDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Jeffrey D. BrawnDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Scott R. LossDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Marilyn O. RuizDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Daniel B. HayesDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Edward D. WalkerDepartment of Fisheries and Wildlife, and Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan; Department of Environmental Studies, Emory University, Atlanta, Georgia; Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin; Department of Natural Resources and Environmental Sciences, Program in Ecology, Evolution, and Conservation Biology, and Department of Pathobiology, University of Illinois, Champaign, Illinois; Conservation Biology Graduate Program, University of Minnesota, St. Paul, Minnesota

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Recent field studies have suggested that the dynamics of West Nile virus (WNV) transmission are influenced strongly by a few key super spreader bird species that function both as primary blood hosts of the vector mosquitoes (in particular Culex pipiens) and as reservoir-competent virus hosts. It has been hypothesized that human cases result from a shift in mosquito feeding from these key bird species to humans after abundance of the key birds species decreases. To test this paradigm, we performed a mosquito blood meal analysis integrating host-feeding patterns of Cx. pipiens, the principal vector of WNV in the eastern United States north of the latitude 36°N and other mosquito species with robust measures of host availability, to determine host selection in a WNV-endemic area of suburban Chicago, Illinois, during 2005–2007. Results showed that Cx. pipiens fed predominantly (83%) on birds with a high diversity of species used as hosts (25 species). American robins (Turdus migratorius) were marginally overused and several species were underused on the basis of relative abundance measures, including the common grackle (Quiscalus quiscula), house sparrow (Passer domesticus), and European starling (Sturnus vulgaris). Culex pipiens also fed substantially on mammals (19%; 7 species with humans representing 16%). West Nile virus transmission intensified in July of both years at times when American robins were heavily fed upon, and then decreased when robin abundance decreased, after which other birds species were selected as hosts. There was no shift in feeding from birds to mammals coincident with emergence of human cases. Rather, bird feeding predominated when the onset of the human cases occurred. Measures of host abundance and competence and Cx. pipiens feeding preference were combined to estimate the amplification fractions of the different bird species. Predictions were that approximately 66% of WNV-infectious Cx. pipiens became infected from feeding on just a few species of birds, including American robins (35%), blue jays (17%, Cyanocitta cristata), and house finches (15%, Carpodacus mexicanus).

Author Notes

Reprint requests: Gabriel L. Hamer, Department of Fisheries and Wildlife, 13 Natural Resources, Michigan State University, East Lansing, MI 48910, E-mail: ghamer@msu.edu.
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