Sunday, April 19, 2009

Answer to Case 66

Answer: Scolex of Taenia solium.

"Pathresident" got this one correct. Nice job!

This is the scolex (head) of the pork tape worm, T. solium, distinguished by its size (approximately 1 mm wide), 4 suckers, and armed rostellum (hooklets on the rounded projection from its scolex). The closely related beef tapeworm, T. saginata, has 4 suckers but no hooklets on its rostellum. The scolex is occasionally identified in feces, and when present, allows for definitive speciation of the Taenia tapeworms, which otherwise look very similar in gross appearance. Identifying the number of uterine branches in the proglottids is the only other way to tell the 2 species apart. The eggs of both are identical and only identify the presence of a Taenia species.

Other cestodes may also have a similar appearing scolex: Hymenolepis nana and H. diminuta also have 4 suckers and an armed rostellum, but are much smaller in width (and length) than T. solium, and the scolex is more knob-like. The scolex of Dipylidium caninum is also similar, but is also much smaller and has a retractable armed rostellum, so the hooklets may appear to be internalized. Finally, the scolex of Echinococcus spp. is also armed with 4 suckers, but the adult tapeworm is only found in dogs and other canids, and NOT humans. Therefore, as mentioned by the first commenter, this would only be found in dog feces, not human.

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