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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Cestodes

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Taenia saginata Beef Tapeworm : Parasitology

T. saginata inhabits the human jejunum, where it may live for up to 25 years and grow toa maximum length of 10μm.

BEEF TAPEWORM

Taenia saginata : PARASITOLOGY

T. saginata inhabits the human jejunum, where it may live for up to 25 years and grow toa maximum length of 10μm. Its 1-mm scolex lacks hooklets but possesses the four suck-ing discs typical of most cestodes (Fig 57 – 1A). The creamy white strobila consists of 1000 to 2000 individual proglottids. The terminal segments are longer (20 mm) than they are wide (5 mm) and contain a large uterus with 15 to 20 lateral branches; these charac-teristics are useful in differentiating them from those of the closely related pork tape-worm, T. solium. When fully gravid, strings of 6 to 9 terminal proglottids, each containing approximately 100,000 eggs, break free from the remainder of the strobila. These muscu-lar segments may crawl unassisted through the anal canal or be passed intact with the stool. Proglottids reaching the soil eventually disintegrate, releasing their distinctive eggs. These eggs are 30 to 40μm in diameter, spherical, and possess a thick, radially striated shell (Fig 57 – 1B). In appropriate environments, the hexacanth embryo may survive for months. If ingested by cattle or certain other herbivores, the embryo is released, pene-trates the intestinal wall, and is carried by the vascular system to the striated muscles of the tongue, diaphragm, and hindquarters. Here it is transformed into a white, ovoid (5 by 10 mm) cysticercus (Cysticercus bovis). When present in large numbers, cysticerci impart a spotted or “measly” appearance to the flesh. Humans are infected when they ingest in-adequately cooked meat containing these larval forms.



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