Coastal freshwater runoff is a risk factor for Toxoplasma gondii infection of southern sea otters

This study connected the felid-shed parasite Toxoplasma gondii to deaths of threatened southern sea otters along the California coast. Because cats are the only definitive hosts that shed environmentally resistant oocysts, the authors hypothesized that land-based runoff carries cat-derived oocysts into nearshore waters where filter-feeding prey concentrate them. By mapping otter infection against coastal freshwater outflow, they found that otters living near major runoff plumes had significantly higher Toxoplasma exposure. The work provided strong epidemiological evidence for terrestrial-to-marine pathogen flow and implicated both wild and domestic cats in marine mammal disease. It became a foundational study linking cat parasite ecology, watershed pollution and the conservation of a marine sentinel species, and it influenced policy on cat feces disposal.