Urban Land Use Predicts West Nile Virus Exposure in Songbirds

Abstract

Urbanization is a widespread phenomenon that is likely to influence the prevalence and impact of wildlife pathogens, with implications for wildlife management and public health policies toward zoonotic pathogens. In this study, wild songbird populations were sampled at 14 sites along an urban rural gradient in the greater metropolitan Atlanta (Georgia, USA) area and tested for antibodies to West Nile virus (WNV). The level of urbanization among sites was quantitatively assessed using a principal component analysis of key land use characteristics. In total, 499 individual birds were tested during the spring and summer over three years (2004-2006). Antibody prevalence of WNV increased from rural to urban sites, and this trend was stronger among adult birds relative to juveniles. Furthermore, antibody prevalence among Northern Cardinals (Cardinalis cardinalis) was significantly higher than in other songbird species along the urban gradient. Findings reported here indicate that ecological factors associated with urbanization can influence infection patterns of this vector-borne viral disease, with likely mechanisms including changes in host species diversity and the tolerance or recovery of infected animals.

Supersuppression: Reservoir Competency and Timing of Mosquito Host Shifts Combine to Reduce Spillover of West Nile Virus

“…Consistent with findings from other avian WNV studies in Georgia, 9,10,27 seroprevalence rates for northern cardinals were significantly higher than most other species. They also represented the largest overall proportion of blood meals, suggesting that they are a highly used host across the Atlanta area.…”

“…7 In addition, both passive dead bird surveillance as well as active live bird surveillance have also indicated consistent yearly WNV infection among avian hosts in Atlanta at levels consistent with rates found in other urban centers such as Chicago. [7][8][9][10][11] However, a total of only 330 human cases have been reported in Georgia since 2001 (incidence of 3.3 per 100,000), in contrast to the 2,088 human cases from Illinois since 2002 (incidence of 16.2 per 100,000). 2 With trends in the enzootic infection levels among hosts and vectors in Atlanta similar to those seen in cities with five times the human incidence, the reason for the lack of human WNV spillover in Atlanta and the southeastern region in general has remained unclear.…”

Regional Differences in the Association Between Land Cover and West Nile Virus Disease Incidence in Humans in the United States

“…9 In the Deep South, two different studies found increased seroprevalence in birds as urbanization increased. 7,10 These two studies did not use a land cover dataset to classify urban or suburban land use in their respective studies: one used an urban score based on human population density and forest cover, 7 whereas the other used field observations to make land use classifications. 10 Therefore, it is possible that what they classified as urban on a small scale may not have been classified as urban in the NLCD 2001 dataset, which provides uniform land cover classifications across the United States.…”

“…Identifying predictive covariates of WNV transmission should, therefore, be considered a key part of pathogen management. Numerous studies have reported associations between different land cover types and WNV disease incidence in humans, [3][4][5][6] seroprevalence or infection rates in birds 7 and wild and domesticated mammals, [8][9][10] and infection rates in mosquitoes. 11,12 However, the strength and direction of these correlations have varied considerably.…”

Persistent impacts of West Nile virus on North American bird populations

“…WNV is hypothesized to influence bird populations through reductions in survival, which can be influenced by various biotic and abiotic factors, including age (12), climate (13,14), and regional environment heterogeneity (15). In addition, a number of studies suggest that the impact of WNV on bird populations increases with human land use (16,17). Understanding the contribution of disease to annual variation in survival across space and time requires rigorous demographic analyses that take into account these factors.…”