Tapeworm infection is acquired by eating raw or undercooked meat of infected animals. Beef generally carry Taenia saginata while pigs carry Taenia solium. The larvae from the infected meat develop in the human intestine into the adult tapeworm -- which grows and can attain lengths greater than 12 feet.

Tapeworms are segmented, with each segment or proglottid capable of producing eggs. Eggs are dispersed by individual or groups of proglottids detaching and passing out with the stool. The groups of proglottids from the beef tapeworm are capable of movement and actively crawl out through the anus.

Adults and children with tapeworm (T. solium, pork tapeworm only) can, if appropriate hygiene is lacking, become self-infected by ingesting eggs from their tapeworm which were picked up on their hands while wiping or scratching the anus.

Additionally, these individuals can expose other individuals to T. solium eggs, usually via food handling. Ingested eggs hatch in the intestinal track and the larvae migrate through the tissues, where they encyst. If larvae migrate to the brain, they can cause seizures and other neurological problems. This condition is called cysticercosis.

Certain freshwater fish and salmon may also carry a tapeworm called Diphyllobothrium latum (see diphyllobothriasis).