Urban Ecology and Epidemiology of West Nile Virus in Atlanta, Georgia Open Access

Levine, Rebecca Cela Sturman (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/ff3655435?locale=en


West Nile virus (WNV) is an endemic mosquito-borne pathogen that impacts the health of humans and wildlife in the United States. In the eastern US, human cases of WNV arise from spillover transmission of the urban enzootic cycle between passerine birds and Culex mosquitoes. Intensive transmission among the hosts and vectors does not always lead to human outbreaks, as is the case in Atlanta, Georgia. The goal of this dissertation was to investigate certain extrinsic ecological conditions in Atlanta that may result in reduced WNV spillover transmission rates. To address this goal, I conducted comprehensive multi-season, multi-habitat, longitudinal WNV surveillance of avian hosts and mosquito vectors, characterized the avian species community, and described mosquito host-feeding patterns in Atlanta from 2010-2012. I isolated WNV from approximately 1% of birds, most of which were Northern Cardinals and recorded an overall avian seroprevalence of nearly 30%, which was significantly higher among Northern Cardinals, Blue Jays, and the 3 members of the Mimid family, yet notably low among American Robins. Examination of the temporal mosquito host-feeding patterns showed a marked shift from American Robins in the early half of the season to Northern Cardinals during the late half of the season. I therefore rule out American Robins as superspreaders in Atlanta and instead posit that Northern Cardinals and perhaps the Mimid family act as WNV "supersuppressor" species, which help slow WNV spillover transmission in the area. I also detected an amplification effect, in which increased host diversity resulted in increased rates of infection, the first empirical evidence for this effect in a mosquito-borne system. I suggest that this effect is driven by an over-abundance of Northern Cardinals and members of the Mimid family, which may cause optimal hosts to be more rare and therefore to be present primarily in more species-rich areas. Finally, I note that urban old-growth forest patches may provide an additional measure of protection against spillover transmission by increasing the WNV amplification fraction on supersuppressor species. This study successfully combines ecological and epidemiological approaches to uncover some of the complex factors governing WNV transmission in an urban area.

Table of Contents

Chapter 1: Introduction 1.1 Emerging Infectious Diseases: 1 1.2 West Nile Virus: 2 1.3 Urban Areas and WNV: 4 1.4 Ecology of WNV Spillover: 6 1.5 Research Goals: 9

Chapter 2 : Limited Spillover to Humans from West Nile Virus Viremic Birds

2.1 Introduction: 11 2.2 Materials and Methods: 12 2.3 Results: 14 2.4 Discussion: 15 2.5 Conclusion: 18

Chapter 3 : Timing Is Everything: Northern Cardinals, American Robins, and the Suppression of West Nile Virus Transmission

3.1 Introduction: 19 3.2 Materials and Methods: 21 3.3 Results: 29 3.4 Discussion: 34 3.5 Conclusion: 41

Chapter 4 : Avian Species Diversity and Amplification of West Nile Virus

4.1 Introduction: 43 4.2 Materials and Methods: 46 4.3 Results: 50 4.4 Discussion: 52 4.5 Conclusion: 57

Chapter 5: Conclusion

5.1 Summary: 58 5.2 Further Research: 61 Figures Figure 1: 67 Figure 2: 68 Figure 3: 69 Figure 4: 70 Figure 5: 71 Figure 6: 72 Figure 7: 73 Figure 8: 74 Figure 9: 75 Figure 10: 76 Figure 11: 77 Figure 12: 78 Figure 13: 79 Figure 14: 80 Tables Table 1: 81 Table 2: 82 Table 3: 83 Table 4: 84 Table 5: 85 Table 6: 86 Table 7: 89 Table 8: 90 Table 9: 91 Table 10: 92 Table 11: 93 Table 12: 94 Table 13: 95 References Cited: 96

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