The parasite toxoplasma gondii can be in the feces of inside / outside cats, and can survive sewage treatment and then travel down rivers until it gets to the sea. (communityconcernforcats.org)
«Egress and invasion are significantly similar between malaria and toxoplasma parasites. (sciencedaily.com)
While a study in the British Medical Journal concluded that contact with cats was not a major risk factor for toxoplasma infection, pregnant women should take care when cleaning litter trays. (cats.org.uk)