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OVERVIEW

Only kings, presidents, editors, and people with tapeworms have the right to use the editorial “we.”

—Mark Twain

Overview

Cestodes are long, ribbon-like helminths that have gained the common appellation of “tapeworm” from their superficial resemblance to sewing tape. Although improvements in sanitation have dramatically reduced their prevalence in the United States, they continue to inhabit the bowels of many of its citizens. In some parts of the world, people take purgatives regularly to rid themselves of these large, repulsive intestinal parasites. Ironically, when a human serves as the definitive host for tapeworms (when they harbor adult worms), it is usually of little medical consequence to that person; the intestinal form of these creatures rarely causes serious harm. In contrast, clinical disease is a greater concern when people serve as intermediate hosts (harbor larvae), because it is the presence of cysts in tissue that is most dangerous. Life cycles and characteristics of the six most important tapeworms infecting humans are summarized in Table 56–1.

TABLE 56–1Intestinal and Tissue Tapeworms

PARASITOLOGY

MORPHOLOGY

Like all helminths, tapeworms lack vascular and respiratory systems. In addition, they are devoid of both gut and body cavities. Nutrients are absorbed across their surface cuticle, and the internal organs are embedded in solid parenchyma. The adult is divided into three distinct parts: The “head” or scolex; a generative “neck”; and a long, segmented body called the strobila. The scolex typically measures less than 2 mm in diameter and is equipped with muscular sucking disks used to attach the worm to the intestinal mucosa of its host. (In one genus, Dibothriocephalus, the disks are replaced by two grooves called bothria.) As a further aid in attachment, the scolex of some species possesses a retractable protuberance, or rostellum, armed with ...

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