Answer to the Parasite Case of the Week 749: Adult tapeworm in the family Diphyllobothriidae (Diphyllobothrid), a.k.a., the broad fish tapeworm 🐟.
As astutely noted by Idzi Potters, "The proglottids of this tapeworm are gravid - the brown central points represent large numbers of dark eggs concentrated in a centrally positioned uterus. As the gravid proglottids are craspedote and wider than they are long, this points towards a Diphyllobothriid tapeworm (possibly Dibothriocephalus). An easy way to confirm this is to cut open a proglottid and expel some of the typical eggs. But for exact species determination, molecular tools should be deployed."
We didn't perform molecular testing to determine the exact genus and species, but we did confirm the worm's identity by expelling some of the eggs from the uterus. They looked something like the eggs from this previous case of the week.
Blaine and I described the current status of known Diphyllobothrids to infect humans in our chapter on Parasites of the Gastrointestinal Tract:
"The species implicated in human disease, and their current taxonomic status and broad geographic distributions, are Adenocephalus pacificus (southern South America, southern Asia), Dibothriocephalus latus (Holarctic), D. nihonkaiensis (Asian Pacific, eastern Russia, Pacific Northwest), D. dendriticus (Holarctic), D. dalliae (Alaska and Siberia), D. ursi (North America), Diphyllobothrium stemmacephalum (circumpolar), and D. balaenopterae (circumpolar). Two additional species implicated in human disease, “Diphyllobothrium” cordatum and “D.” lanceolatum, both circumpolar in distribution, are tentatively placed in Diphyllobothrium but will probably undergo generic transfer in the future (Kuchta et al., 2015; Waeschenbach et al., 2017)." As several of you have pointed out, Diphyllobothrium latum is now Dibothriocephalus latus 😊.
Like most cases that we receive in our lab, we sadly didn't receive the travel history for the patient, and therefore we can't make any guesses as to the identity of this tapeworm based on known distributions.
2 comments:
craspedote? Meaning in context?
Hi Anonymous, in the context of tapeworm proglottids, the term "craspedote" refers to a type of proglottid that has an overlapping posterior margin, meaning that the posterior edge of one proglottid extends over the anterior edge of the next proglottid in the chain. This creates a distinctive, overlapping appearance, as opposed to "acraspedote" proglottids, where the posterior margin does not overlap the next proglottid. This morphological characteristic is useful for the identification and classification of different tapeworm species. I hope this explanation is useful!
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