The beef tapeworm Taenea saginata can be up to 12 feet in length (see picture on the right) once it reaches adult stage. Here’s how this works: A cow or pig eats vegetation infected with the egg or proglottids (a piece of the tapeworm). One of the immature stages of the tapeworm embeds and migrates through the tissues of the animal. A human comes along and eats the undercooked or raw meat and the immature parasite matures in the intestinal tract of the human.
Taenia solium, the pork tapeworm, is from one to several meters in length and is able to produce two diseases in the human, the taeniosis and cysticercosis. The taeniosis (intestinal form) is an exclusive disease of humans, often asymptomatic, and can perhaps maintain the infection for years. The main clinical manifestation is the frequent spontaneous elimination of proglottids in the feces. Approximately 5% to 40% of people with taeniosis develop into cysticercosis, confirming the fecal-oral contamination and infections of people associated with them.