FORECASTING VIBRIO PARAHAEMOLYTICUS IN A CHANGING CLIMATE

The distribution, transmission and adaptation patterns of infectious diseases are changing worldwide. Though there are many potential mechanisms that can transmit infectious agents to new areas, the ability of pathogens to persist in new locations can be largely attributed to changing climate conditions, especially in temperate regions. Vibrio parahaemolyticus, a naturally occurring bacteria in most marine and estuarine systems, provides a model example of these globally observed climate-related changes to disease dynamics that are occurring locally in the Northeast, US. Like many Vibrio species, pathogenicity in human hosts is believed to be limited to a subset of strains, whereas the overall population of various strains acts as a part of the microbial community contributing to nutrient cycling and the food web. Until recently, global V. parahaemolyticus disease incidence was sporadic and mainly limited to the warm water regions of Asia, India and the Gulf of Mexico in the US. However, disease from pathogenic V. parahaemolyticus has become endemic in cold and temperate-water regions, including parts of Europe, Canada, and the Northwest and Northeast regions of the US that were historically considered low risk for V. parahaemolyticus disease. The consumption of raw or undercooked oysters is the most common route of V. parahaemolyticus infection, and the recent increase of illnesses in the Northeast has been simultaneous with a significant expansion of the regional oyster fishery. The application of traditional environmental indicators such as water temperature and salinity that were developed in warm water regions to mitigate and manage disease risk have not been completely successful indicators for preventing the public from becoming sick due exposure to pathogenic V. parahaemolyticus in this region. A combination of statistical modeling and population genomic analysis was used to characterize the ecology of V. parahaemolyticus in the Great Bay estuary (GBE) to better inform monitoring and forecasting strategies to manage the impacts to public health and the shellfish industry of these local outbreaks, since solutions from the warm and tropical regions may not be effective in the temperate regions. Forecasting models were developed by combining ecological variables with seasonality and trend analysis to analyze long-term surveillance data collected since 2007 (Chapter 1). High resolution investigation of the interactions between V. parahaemolyticus and the plankton community was then used to characterize the environmental variables that contribute to the development of optimal conditions for V. parahaemolyticus growth over the course of a season (Chapter 2). Finally, genomic analysis of V. parahaemolyticus was conducted to investigate how the environment influences population structure in the GBE and may contribute to observed V. parahaemolyticus population dynamics (Chapter 3). Continued long-term surveillance and forecasting tools are needed to address many of the currently unresolved questions surrounding V. parahaemolyticus ecology that are important to better understand its role as both a member of the environmental community and an agent of human disease. This research provides an in-depth picture of the ecological drivers that underlie the interactions of V. parahaemolyticus with its environment and contributes to the development of effective forecasting tools for public health and shellfish management under current and future climate scenarios