Answer to Case 578

Answer to Parasite Case of the Week 578:Hymenolepisspecies. I agree with Blaine and Idzi that this is likelyH. nanabased on the size of the eggs, but I also couldn ' t see the polar filaments to be certain.What wecansee in this case are the following features:Thin outer tegument with loose underlying stroma, and segmented nature (proglottids) consistent with a tapeworm.Multipleindividual eggs measuring approximately 35 micrometers in greatest dimension, with inner and outer membranes. Internal refractile hooklets in some eggs (pink arrow heads in image below and inset). Combined, these features all point towardsHymenolepis nana.  I emphasized that the eggs are found singly to differentiate them from the eggs ofDipylidium caninumwhich are generally found in packets - even in tissue sections. You can see a previous case ofD. caninumin tissue sectionHERE. Note how the " rice grain " proglottids ofD. caninumare 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 ofTaeniaspecies which have a single striated shell. You can see a case ofTaeniain tissue section HERE. The proglottids ofTaeniasp. are much larger than those ofHymenolepis,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!
Source: Creepy Dreadful Wonderful Parasites - Category: Parasitology Source Type: blogs