Saturday, April 14, 2012

Answer to Case 204

Answer:  Taenia saginata (or T. asiatica)

This case demonstrates numerous features of Taenia species, including gravid proglottids that are longer than they are wide (compared to proglottids of Diphyllobothrium latum which are wider than they are long), lateral uterine branches originating from a central uterine stem, and round to oval eggs with internal hooklets and radial wall striations.  As mentioned by Anonymous, "The eggs of T.saginata and T solium are not distinguishable from each other."  This also holds true for the gross appearance of the proglottids.

Instead, differentiation of the human Taenia species is accomplished by:
1.  Examining the features of the scolex (which is usually not present in the specimen unless obtained after anti-helminth administration) AND/OR
2.  Examining the number of primary lateral uterine branches in a gravid proglottid.  As some mentioned, T. solium has less than 13 primary lateral uterine branches while T. saginata and T. asciata have greater than 13-15 primary lateral uterine branches.  Determining the number of branches is traditionally accomplished by clearing the proglottid in lactophenol or another chemical and/or injecting India ink in the proglottids.  The branches are then counted from a single side of the uterine stem (not both sides), being sure to count only the primary branches (right as they come off of the central stem) and not the terminal branches.

The preparation shown here was created by clearing a gravid proglottid in Euparal essence. We also attempted to clear the proglottids in lactophenol but the results were not as good.  After clearing, the proglottid was simply pressed between 2 glass slides, using Euparal Mounting Media as a permanent and flexible mountant.  In my lab, we try to avoid India ink injection, given that this requires a considerable amount of proglottid manipulation which potentially increases the risk of exposure to Taenia eggs.  Recall that ingestion of Taenia solium eggs may result in cysticercosis.

In addition to pressing the proglottids between 2 slides, we also sent a proglottid for histologic sectioning.  The section shown here nicely highlights the presence of >15 primary lateral uterine branches.  We don't typically use histologic sectioning in my lab, but it is useful as a back-up or confirmatory method.

Finally, as anonymous points out, T. asiatica should also be considered in this case since it has the same number of primary lateral uterine branches as T. saginata.  It is only by molecular analysis or examination of the scolex that the 2 can be differentiated.  The distribution of Taenia asiatica is limited to Asia and is seen mostly in Thailand, Korea, China, Indonesia and Taiwan.

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