Causal Agents:
The cestodes (tapeworms) Taenia saginata (beef tapeworm) and T. solium (pork tapeworm).  Taenia solium can also cause cysticercosis.

Life Cycle:

Life cycle of Taenia saginata and Taenia solium
Humans are the only definitive hosts for Taenia saginata and Taenia solium.  Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment.  Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids .  In the animal's intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci.  A cysticercus can survive for several years in the animal.  Humans become infected by ingesting raw or undercooked infected meat .  In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years.  The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine .  Length of adult worms is usually 5 m or less for T. saginata (however it may reach up to 25 m) and 2 to 7 m for T. solium.  The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day).  T. saginata adults usually have 1,000 to 2,000 proglottids, while T. solium adults have an average of 1,000 proglottids.  The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces.  T. saginata may produce up to 100,000 and T. solium may produce 50,000 eggs per proglottid respectively.

Geographic Distribution:
Both species are worldwide in distribution.  Taenia solium is more prevalent in poorer communities where humans live in close contact with pigs and eat undercooked pork, and in very rare in Muslim countries.