Answer to Case 578

Answer to Parasite Case of the Week 578: Hymenolepis species. I agree with Blaine and Idzi that this is likely H. nana based on the size of the eggs, but I also couldn't see the polar filaments to be certain.

What we can see in this case are the following features:

1. Thin outer tegument with loose underlying stroma, and segmented nature (proglottids) consistent with a tapeworm.
2. Multiple individual eggs measuring approximately 35 micrometers in greatest dimension, with inner and outer membranes. 
3. Internal refractile hooklets in some eggs (pink arrow heads in image below and inset). 

Combined, these features all point towards Hymenolepis nana.  I emphasized that the eggs are found singly to differentiate them from the eggs of Dipylidium caninum which are generally found in packets - even in tissue sections. You can see a previous case of D. caninum in tissue section HERE. Note how the "rice grain" proglottids of D. caninum are much different than the continuous chain of proglottids seen here.

Finally, I mentioned the presence of inner and outer membranes of the eggs in this case to differentiate them from the eggs of Taenia species which have a single striated shell. You can see a case of Taenia in tissue section HERE. The proglottids of Taenia sp. are much larger than those of Hymenolepis, and the eggs are found with the thin central uterine stem and lateral branches.

Thanks again to Dr. Rachael Liesman for donating this educational case!