Causative agent? Taenia solium
How is this organism acquired? Through ingestion of EGGS. The adult worm is acquired through ingestion of larvae. This is a favorite test question.
Differential diagnosis
First, you can tell this is a cestode due to the presence of calcaneous corpuscles (small calcified bodies) which are unique to cestodes (arrows).
The presence of a single hooked protoscolex within the small folded cyst tissue is characteristic of T. solium. However, you should also consider the following when looking at a larval cestode in tissue. All can be found in muscle, as in this case.
1. Echinococcus species - expect to see multiple cysts. In E. granulosus, each cyst contains multiple hooked protoscoleces. (Note that T. solium cysticeri only have only one hooked scolex per cyst) Protoscolex formation is rare in E. multilocularis, whose cysts are usually sterile in humans.
2. Spirometra species - do not form protoscoleces, so no hooks or suckers will be seen. The larva is solid-bodied and is not surrounded by a bladder.
3. Taenia multiceps and Taenia serialis (coenurus) - Like E. granulosus, cysts contain multiple protoscoleces with typical hooks and suckers, but are surrounded by a thin wall without a laminated membrane.
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