| Summary: | West Nile virus (WNV) infection rates in wild birds and mosquitoes, and the blood-feeding patterns of mosquitoes were examined at two study sites in Baton Rouge, Louisiana to identify the potential avian reservoir hosts and mosquito vectors of West Nile virus (WNV). Blood samples from a total of 2,442 wild birds in the orders Passeriformes, Piciformes and Columbiformes were collected from May 2006 to April 2008 and tested for the presence of WNV RNA using RT-PCR and antibodies to WNV using an epitope-blocking ELISA. WNV was detected in 3.77% of wild bird blood samples and antibodies to WNV were detected in 12.29% of samples. The species with the most historically infected individuals were Northern Cardinal, House Sparrow, American Goldfinch, White-throated Sparrow, Yellow-rumped Warbler, Brown Thrasher, Northern Mockingbird, Carolina Wren, Tufted Titmouse and Mourning Dove. The detection of ELISA positive bird blood samples were correlated with the detection of RT-PCR positive samples. The potential for South-central Louisianas winter resident and migrant passerines to act as long-distant transport agents for West Nile virus was demonstrated. A total of 21,644 female mosquitoes were collected and tested using RT-PCR. WNV was detected in 4.1% of mosquito pools tested with the greatest infection rates in mosquitoes of the genus Culex. The greatest number of positive pools were comprised of Culex quinquefasciatus mosquitoes. Vertebrate hosts of 120 female mosquitoes were successfully identified using PCR amplification and sequencing of the Cytochrome-b gene. Culex quinquefasciatus females host sources were avian (49.4%), mammalian (48.3%) and amphibian (2.2%) with the Northern Cardinal, Brown Thrasher, Blue Jay, Downy Woodpecker and Eastern Bluebird as the most common avian hosts and the domestic dog, Human, Northern Raccoon, White-tailed Deer and domestic cow as the most common mammalian hosts. No seasonal shift in the proportion of Culex quinquefasciatus feeding on avian or mammalian hosts was detected during this study. Stationary point counts and other observations were used to estimate wild bird species diversity and species abundance and at the study sites. Forage ratios in Culex quinquefasciatus were calculated using species abundance estimations and the frequency of bloodmeals identified from those species.
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