Taenia saginata Taeniarhynchus saginatus Beef Tapeworm Figure 235

The adult tapeworm lives only in the small intestine of humans and so far has never been found naturally in any other definitive host.

Experimental infections have been established in immunosuppressed golden hamsters, but without obtaining gravid proglottids (Verster, 1971). The tapeworm is acquired by ingesting raw or undercooked beef infected with larvae. The larvae evaginate in the small intestine of the host. After digestive juices and bile promote the evagination of the scolex through the bladder wall, this structure attaches to the intestinal wall, probably by burrowing through the intestinal villi with the unarmed rostellum, penetrating a crypt of Lieberkuhn while simultaneously anchoring to

Fig. 23.2 Electron micrograph of Taenia solium metacestode surface, illustrating microvilli (arrow)

Growth of the adult tapeworm then proceeds continuously from the neck region by an ever-lengthening chain of proglottids; 4-6 months after infection, the tapeworm begins to eliminate gravid proglottids containing 50000-80000 infective eggs, which are shed in the stool.

When infective eggs are ingested by cattle in contaminated fodder or water, the oncospheres penetrate the intestinal wall and are carried to various tissues, mostly the heart and masseter muscles but also throughout the musculature, where they develop into larvae or cysticerci. Ingestion of viable larvae in raw or undercooked beef by humans can then produce a new adult tapeworm.

Fig. 23.2 Electron micrograph of Taenia solium metacestode surface, illustrating microvilli (arrow)

Fig. 23.4 Transmission electron micrograph through Taenia solium egg. Arrow, embryophore. O, oncosphere
Fig. 23.3 Taenia sp. eggs. Light micrograph showing typical embryophore outer shell (arrow, E). Reproduced by permission from Flisser et al. (1982)

neighboring villi by all four suckers, similar to the mechanism that has been identified for Echinococcus granulosus in experimental dogs and in experimental T. solium infections in hamsters.

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