Cestode proglottids and scolices

Common cestodes include Taenia, Dibothriocephalus, Hymenolepis, and Dipylidium. The primary diagnostic forms are the mature (gravid) proglottids and the scolex. Proglottids are macroscopic structures passed in the stool; these may be submitted for laboratory examination. Proglottids increase in size as they grow from immature to gravid. Proglottids of Taenia, Dipylidium, and Dibothriocephalus are large (length 0.5 to 1.5 cm), while proglottids of Hymenolepis species are much smaller (0.5 mm x 1.0 mm).
Distinguishing these species requires careful gross and macroscopic examination. The scolices are quite small (diameter ≤1 mm) but can be examined under a dissecting or light microscope to identify hooklets and suckers for speciation.
(A) Gross Taenia species (upper panel), with Taenia saginata proglottid and scolex (lower left panel) and Taenia solium proglottid and scolex (lower right panel). Note the distinct hooklets of T. solium seen on the scolex distinguishing it from T. saginata.
(B) Gross Dibothriocephalus species (upper panel), with Dibothriocephalus latus proglottid and scolex (lower panel). Note the elongated folded sucker of this species.
(C) Gross Hymenolepis species (upper panel; maximum width 1 mm width and length 40 mm), with Hymenolepis nana (lower left panel) and Hymenolepis diminuta (lower right panel). The proglottids and scolex of these species are difficult to distinguish.
(D) Gross Dipylidium species (upper panel; length 10 to 40 cm) with Dipylidium caninum (lower panel). Note the double pored proglottid distinctive of this species.
The proglottids of Taenia have >14 ovarian branches (T. saginata, A) or <14 ovarian branches (T. solium, B). T. solium also has a scolex with hooklets (A, lower right panel). D. latus has a distinctive proglottid containing a "central rosette" that is visible with or without ink infusion preparation (B, upper panel). Hymenolepis nana (C, lower left panel) and H. diminuta (C, lower right panel) can be distinguished by the presence of polar filaments in the eggs of H. diminuta.