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More Information about Marine Organisms as Disease Vectors
Background
A major route for human exposure to marine pathogens is the consumption of fish and shellfish. The American oyster, Crassostrea virginica, is a vector for human pathogens, including Norwalk-like viruses, Cryptosporidium spp. and Vibrio spp. Like other filter-feeding bivalves, oysters harbor and concentrate pathogens that occur in their marine habitat and transfer them to humans when the oysters are eaten. The hazards posed by bioaccumulation of pathogens in shellfish are compounded by the traditional consumption of certain shellfish in raw or only minimally cooked dishes.
There is clearly a need to understand the role of marine organisms as vectors of human disease pathogens and to develop predictive models that will more effectively assess the risk of consumption as well as target surveillance efforts to protect consumers from disease. The oyster lives in coastal waters that have highly variable water quality (e.g., low dissolved oxygen, high pH) and substantial pollutant loadings (e.g., metal and organic pollutants). Laboratory findings suggest that water quality factors such as pH and O2 levels, as well as the concentration of metal and organic pollutants, can impact the ability of oysters to accumulate, or biointensify, human pathogens, either externally in the mantle cavity, or internally, within the tissues of the animal.
Environmental stressors to be examined include ranges of pH and O2 conditions characteristic of estuarine environments, as well as the presence or absence of representative metal and PAH contaminants. Opportunistic Vibrio spp. are targeted in these studies because:
- Members of this bacterial genus, including V. cholerae, V. parahaemolyticus and V. vulnificus, lead the list of bacterial pathogens responsible for outbreaks of human disease associated with shellfish consumption;
- Members of the genus are ubiquitous in aquatic and terrestrial environments; and
- These bacteria are commonly associated with disease in a wide variety of marine organisms.