Giardia is one of them. Giardia in cats starts in the intestine but ultimately, it spreads through poop. It could be poop in a litter box that spreads over to another pet (or even a human ...

Cats can shed gastrointestinal parasites in their feces, including roundworms, tapeworms, hookworms, whipworms, heartworms, and single-celled organisms including Giardia and Toxoplasma gondii.