Neglected Consequences: Role of Introduced Aquatic Species in the Spread of Infectious Diseases

Introduction of aquatic organisms to new ecosystems has led to massive alterations to the structure and function of natural ecosystems, and to extinction of native flora and fauna. The ecological impacts caused by exotic aquatic species worldwide have been widely recognized, but the past and potential human health impacts of these introductions have been largely ignored. This review identifies several modes by which introduced aquatic species negatively impact human health: a) the direct introduction of human pathogens and/or their hosts; b) the introduction of pathogens of species upon which humans depend; and c) structural and functional alterations of ecosystems that affect other aquatic species upon which humans depend. The literature review presented here focuses on the first of these modes, presenting examples of either pathogens or hosts of pathogens (or both) that are documented to have been introduced, and that either affect or have the potential to affect human health, and occur in aquatic environments. Documented or suspected cases of introduced species that have caused human health impacts include: a) introduced dinoflagellates, which cause the accumulation of human neurotoxins in shellfish; b) various species of freshwater snails hosting a variety of human disease organisms, including Schistosoma mansoni (the cause of intestinal schistosomiasis), schistosomes that cause swimmers itch (cercarial dermatitis), the liver fluke Fasciola hepatica, and others; c) Vibrio cholerae, the agent of infection of cholera disease; and d) introduced mitten crabs, which can carry a human lung fluke.