Answer to Case 504

Answer:Trichuris trichiura,the human whipworm.It ' s hard to top Blaine ' s excellent description of the diagnostic features for this case:"Trichuris trichiura. If the eggs in utero were not enough, there is also stichocytes and bacillary bands (best seen in the anterior end of the worm within the tissue), polymyarian/coelomyarian musculature, and a strongly nucleated hypodermis. The size and egg morphology rules-outCapillaria philippinensis, which would also be in the intestinal tract and have trichuroid features of stichocytes and bacillary bands. "William Sears also pointed out a helpful feature: " it is telling that the thinner head part is embedded in the tissue and the larger tail is not embedded consistent with whipworm. " Besides the eggs, the location in the tissue is one of the key features. Here are some of these diagnostic features:Eggs with polar plugs (arrows; below):As many of you may know, the whipworm gets it ' s name from it ' s shape - a skinny end and a thicker end, giving the worm a ' whip-like ' shape. Unlike what is typically expected, however, the skinny end is anterior - not posterior. When my students find this puzzling, I ask them what they would rather try to do - insert the thin, needle-like end of the worm into the colonic mucosa, or the fat end? I also ask them what makes more sense - having the end with eggs hanging free in the lumen or caught up in the mucosa? This usually helps them conceptualize the worm ' s morphology, and I think they tend...
Source: Creepy Dreadful Wonderful Parasites - Category: Parasitology Source Type: blogs