Emergence of Terrestrial Parasites in Marine Environments

Waterborne outbreaks of coccidian parasites such as Toxoplasma gondii and Sarcocystis neurona, parasites that belong to the same major protist group as Plasmodium (the agent of malaria) are increasingly causing fatal disease in marine wildlife. Using population genetic and molecular methods to study the evolution, emergence and transmission of pathogenic strains of Toxoplasma and Sarcocystis, our work has identified a marine invasion of new genetic variants produced when two parasites mate inside their definitive hosts (cats in the case of Toxoplasma, opossums in the case of Sarcocystis). Population expansions of the definitive hosts near marine estuarine environments have led to increased deposition of highly infectious oocysts and widespread exposure of marine wildlife to these pathogenic pollutagens after storm events. Co-infection with both coccidian agents (i.e., polyparasitism) has been identified as a serious risk factor predisposing marine mammals to fatal infections.