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The pork tapeworm Taenia solium and the beef tapeworm T saginata are the most common tapeworms of humans. The diseases associated with infection by these organisms have been known since ancient times, being found wherever insufficiently cooked pork or beef is eaten. Human infection with the pork tapeworm is uncommon in the United States and Canada, although larval infection (ie, cysticercosis) of swine may still occur. In many areas of the world, especially Mexico and parts of South and Central America, Africa, southeastern Europe, India, and China, infection with T solium is relatively common. Human infection with the larval stage of T solium (Cysticercus cellulosae), or cysticercosis, is found wherever adult T solium infection is common.1T saginata infection occurs among those who eat raw or insufficiently cooked beef. Human infection with larval T saginata (Cysticercus bovis) almost never occurs.

Humans are the mandatory definitive hosts who disseminate infection to porcine or bovine intermediate hosts. Transmission to swine usually occurs through contaminated soil, where gravid proglottids are deposited with human feces. Eggs can survive for weeks in moist soil. In cattle, grazing lands, water, or cattle feed that is contaminated with infected human feces are sources of infection. Intrauterine infection of calves has been reported.

Adult worms live in the upper small intestine, with T solium measuring 2 to 8 m and T saginata measuring 3 to 10 m. The scolex of the pork tapeworm is distinguished by a crown or rostellum with a double row of hooklets. The scolex of T saginata is without hooks. The gravid uterus holds thousands of eggs, each with a mature 6-hooked (ie, hexacanth) embryo. Eggs are 30 to 40 μm in diameter and similar in both human Taenia species. If the eggs are ingested by a suitable intermediate host such as swine (T solium) or cattle (T saginata), the embryo is liberated, penetrating the intestinal wall and disseminating via the bloodstream. The embryo of T solium may invade all tissues of the body and develops into a cysticercus or bladder worm. Cysticerci are ellipsoidal, white, translucent cysts into which the scolex is inverted.

When infected meat is eaten, the cysticercus is activated by gastric juices and bile, which stimulate evagination of the scolex. The scolex attaches to the jejunal wall, and the embryo becomes a mature tapeworm in 10 to 12 weeks for T saginata and 5 to 12 weeks for T solium. In humans, the eggs of T solium are ingested, and the larval stage may develop in every tissue of the body, a condition known as cysticercosis cellulosae. In tissue, the larvae cause an inflammatory infiltrate of eosinophils, plasma cells, neutrophils, and lymphocytes, with eventual necrosis and fibrosis and subsequent calcification of the parasite.

Clinical Manifestations

Infection with the adult T solium or T saginata is either asymptomatic or associated with only ...

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