Answer to Parasite Case of the Week 633: Fasciola hepatica
Although the fluke was sadly torn in half during retrieval, it has all of the features that allows us to identify it:
As a trematode - it has the flat, leaf-like body shape of a platyhelminth belonging to the Trematoda phylum. On histopathologic examination, trematodes have an outer tegument (with microvillus border, and often with spines), spongy parenchyma with no large cavities, and a digestive tract. Cestodes have a similar appearance, but may have a large cavity (depending on the species and stage), do NOT have a digestive tract or tegumental spines, and have calcareous corpuscles in the stroma.
I don't believe I see see ovarian tubules in this section, although it is hard to tell from this image alone. I also don't see any eggs. This would make sense as Dr. Anderson was not able to express any eggs from the portion of the fluke that he received in the laboratory.
As Fasciola hepatica specifically - the large size of this structure allows us to identify it as either Fasciola hepatica or F. gigantica. We can further identify this fluke as F. hepatica based on the presence of pointed tegumental spines. F. gigantica, in comparison, has tegumental spines with blunt/flattened ends. Other morphologic features (e.g., overall size of the adult and its eggs, features of the acetabulum) can also be used to differentiate F. hepatica and F. gigantica.
Thanks again to Dr. Anderson for sharing this case with us!