Ecological approaches to public health research
Human infectious disease emergence has been linked to anthropogenic environmental changes influencing the distribution, abundance and interactions between pathogens, vectors and hosts. The conceptual frameworks and methodological tools used in ecological research are uniquely suited to study these complex, hierarchically organized systems. I will discuss the history of ecological approaches to public health, from more ‘static’ approaches in disciplines like landscape epidemiology, medical geography and spatial epidemiology to key contributions of dynamic population modeling and integrative approaches to model spatio-temporal patterns of risk. I will illustrate these concepts with my research on the emergence of Ixodes scapularis-borne pathogens in the United States. Following the Lyme disease epidemic, five other pathogens are currently emerging at different rates in the US, providing a unique opportunity to study disease emergence. Specific research questions include (1) what is the critical spatial scale of heterogeneity in human risk of tick-borne diseases and (2) what are the relative contributions of environmental risk (density of infected ticks) and human behavior to infection and disease? and (3) can integrating environmental and disease surveillance data inform us about the processes of disease emergence?
Our research provides evidence that the various components of human risk of infection are determined by processes occurring at different scales. More virulent strains of Borrelia burgdorferi –the Lyme disease agent, occur in northeastern vs. midwestern United States (continental scale); local host community, timing of tick feeding activity and patterns of tick spread drive patterns of tick infection at intermediate scales; landscaping patterns determine peridomestic exposure risk and individual’s behavior drive personal exposure. Beyond these factors driving human exposure to the pathogen, detection of actual disease cases will be influenced by the frequency of asymptomatic infection and the accuracy in diagnoses and reporting. We found that the integration of disease case data with environmental and entomological risk data at multiple spatiotemporal scales provide unique insights into the process of pathogen and tick-borne disease emergence and persistence.