Answer to Case 68
This was a case of diphyllobothriasis caused by Diphyllobothrium sp., most likely D. latum.  The diagnostic features observed were:

• The gross appearance of the worm (segmented) was indicative of a tapeworm (cestode).
• The size of this specimen excluded small tapeworms, such as Hymenolepis nana.
• The proglottids were wider than they were long.  This feature should be carefully considered since the more anterior and middle proglottids of Taenia spp. can also have this appearance.  The more distal proglottids are longer than they are wide in these species.
• The eggs were an average of 66 micrometers in length; an abopercular knob was seen on several.

Often, the scolex is not present on worms passed in the stool, so other methods of species determination must be used.  In Diphyllobothrium spp., the uterus is in the form of a rosette, occupying the middle field of the proglottid and can sometimes be seen as a dark dot in more mature proglottids when examining the whole worm.  These dark dots were seen in some proglottids in Figure A.  In addition, a segment was removed to see if it had a gravid proglottid (containing eggs) by pressing it between two glass slides.  The eggs were oval and operculated, consistent with those of Diphyllobothrium spp.  Eggs from cestodes belonging to the families Taeniidae and Hymenolepididae are round and do not have an operculum.

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