Saturday, August 22, 2015

Answer to Case 361

Answer:  Taenia species

Thank you for all of the great responses! Based on the morphology of eggs that were expressed from the tapeworm proglottids, we were able to identify this as a Taenia species. Note that the eggs are round-oval, have a radially-striated wall, and clearly-visible internal hooklets.

As part of this case, I asked readers to comment on which procedure they used in their lab to identify the specific species of Taenia. Several readers commented that they compressed a proglottid between 2 slides (with or without prior clearing with phenol) before trying to count the primary uterine branches off of the central stem. A few mentioned trying to use India ink injection to highlight the branches, although several individuals mentioned how challenging this can be, especially when the proglottids are submitted in formalin. Others mentioned using histopathologic sectioning to visualize the uterine branches.

We've used all of these techniques in my lab, but I have recently settled on histologic sectioning as my method of choice for examining the uterine branches.  Even though we have had success with all of the methods mentioned above, I prefer the histologic method for the following reasons:

  1. It requires the least amount of proglottid manipulation outside of a biosafety cabinet (important since proglottids may contain potentially infectious eggs).
  2. It doesn't require us to keep phenol or India ink in our lab (two less reagents that require stocking, labelling, monitoring and disposal!)
  3. Submission in formalin doesn't negatively impact our analysis (and is actually the fixative of choice for histology).
  4. We have access to an excellent histology lab that can perform the sectioning and staining within 1-2 days (which I feel is acceptable for patient care). 
So although we don't play around with the proglottids anymore (which can be fun) we now have a reliable and efficient method for determining the species of Taenia proglottids. Here is an image of the histologic sections from this case (CLICK ON IMAGES TO ENLARGE):

I marked the primary uterine branches in the image below to demonstrate that there are >13 branches present, making this T. saginata/T. asiatica.

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