The correct answer is D, Toxoplasma gondii.  Cats are the definitive host for Toxoplasma gondii and can pass oocysts that could contaminate litter boxes.  If a pregnant woman contaminates her hands while changing the litter, she can accidentally ingest oocysts.

Click here to open a new window with a schematic diagram showing the life cycle of Toxoplasma gondii.  Close the new window to return to this page.