Answer to Case 618

 Answer to Parasite Case of the Week 618: Echinococcus granulosus sensu lato species complex

There are many cool features in this cool case. Here are just a few that I thought were worth pointing out:

First, note how you can see a portion of all of the layers of the cyst. Going from the outside-inward, you can see the compressed host tissue, outer most parasite-derived layer (laminated layer), the granular layer, and several brood capsules, each containing multiple protoscoleces.

Within the individual brood capsules are many inverted protoscoleces arising from the granular layer. We even managed to get a section showing how one protoscolex is attached to the cyst granular layer by a thin stalk. Numerous, variably-sized, calcareous corpuscles are also seen: 

Another cool feature in this case is the presence of degenerating protoscoleces within some of the daughter cysts, resulting in freed hooklets. The resultant gritty fluid is referred to as hydatid sand. 

Protoscoleces don't usually evert unless they have been ingested by the definitive canid host. They then mature into the adult worm and live in the gut of the host. I'm guessing that eversion occurred in this case as part of the degenerative process.

Thank you for all of the comments!