Internal parasites are extremely common in cats, especially kittens and outdoor cats. While some parasites are merely unpleasant, others can cause serious health problems and a few are transmissible to humans. Regular fecal screening and appropriate deworming are important parts of responsible cat ownership.
Roundworms
Roundworms (Toxocara cati and Toxascaris leonina) are the most common intestinal parasite in cats. Kittens are often infected through their mother's milk. Adult cats typically acquire roundworms by ingesting eggs from contaminated soil or by eating an infected prey animal. Signs include pot-bellied appearance, poor coat quality, weight loss despite normal appetite, vomiting, and diarrhea. Roundworm eggs are resilient in the environment and can remain viable for years.
Tapeworms
Tapeworms are long flat worms that attach to the intestinal wall. The most common tapeworm in cats (Dipylidium caninum) is transmitted by fleas — cats ingest infected fleas while grooming. Another type (Taenia taeniaeformis) comes from eating infected rodents. Tapeworm segments — which look like small rice grains — may be visible around the cat's anus or in their feces. They may also appear as small dried segments on bedding.
Hookworms
Hookworms (Ancylostoma braziliense and other species) are small worms that attach to the intestinal wall and feed on blood. They cause bloody diarrhea, weight loss, and anemia — especially dangerous in kittens. Hookworm larvae can penetrate skin, which is why walking barefoot on contaminated soil can theoretically transmit hookworm to humans (causing a skin condition called cutaneous larval migrans).