Scanning and transmission electron microscope studies on the efficacy of praziquantel on Hymenolepis nana (Cestoda) in vitro.

The dwarf tapeworm, Hymenolepis nana, was studied by means of scanning and transmission electron microscopy after in vitro exposure to 1, 10, and 100 micrograms/ml of the anthelmintic praziquantel (Droncit) for 5, 15, 30, and 60 min. The resulting vacuolization of the tegument was exclusively confined to the neck region of the tapeworms and was already observed after treatment for 5 min with 1 microgram/ml. This vacuolization finally led to the disruption of the syncytial layer in the apical region of the tegument. The tegumental microtriches and the surface coat remained unaffected. Proglottids of the middle or posterior regions of the worms never showed destruction.