Meta-analysis of published frequencies of the first decade of field-based mortality and seropositivity in avian species affected by West Nile virus in the United States

A meta-analysis approach was used to extract the frequency of avian seropositivity to West Nile Virus (WNV) ( f S) and mortality from WNV ( f M) from the literature published between the years 2001-2010. The indices, f S and f M, were used to represent states of resistance (seropositivity with no or limited mortality) and susceptibility in birds (detection of WNV with mortality), respectively. The indices f S and f M were calculated for each species across publications into different taxonomic strata, year, combined time intervals, and geographic location. The data were analyzed by logistic regression to assess the status of WNV infection amongst different avian taxonomic strata and infer changes of WNV infection status over time. Using level of peak viremia as a proxy for host competence among the avian species, the value of the phylogenetic signal was tested by Blomberg´s K after transformation of the branch lengths. Sixty-three publications were used for the final dataset representing studies performed from 1999 to 2008 and published between 2001-2010. Analysis of both f S and f M demonstrated variability in avian responses to WNV across order, family, and species. When the data were analyzed for f S, the families and species of the orders Ciconiiformes, Galliformes, and Columbiformes had significantly higher f S than that of the Passeriformes (P < 0.0001). Within the Passeriformes, the Corvidae and Cardinalidae families had higher f S than any other family. When the data were analyzed for f M, dead Corvidae and Paridae were most likely to test positive for virus. Temporally, a positive trend of increasing f S was detected in several avian species while the American crow ( Corvus brachyrhynchos ) was the only species with a significant negative trend in f M (P = 0.042). Little to no interaction of geographic location with time was detected within species of birds. A weak but significant phylogenetic signal corresponded to host range, suggesting that the rate of spread of WNV through the avian community was partially dependent of the relatedness of hosts. The meta-data predicted that species within families, and even order, were heterogeneous in their disease susceptibility traits to WNV. The Passeriformes contributed most to this variation. Several trends in various families and orders of birds were observed from which new studies could be pursued. The pooling of data was key in detecting areas where data was lacking and identified aspects of avian responses to WNV could be expanded.