Ultrastructural investigations on the effect of praziquantel on the tegument of five species of cestodes.

Adult Hymenolepis diminuta, H. microstoma, H. nana, Echinococcus multilocularis, and Taenia (Hydatigera) taeniaeformis have been exposed in vitro in media containing 0.1 to 100 micrograms praziquantel/ml. Already after 5 min characteristic tegumental lesions, that were restricted to the growth zone of the neck region, were recognized using both scanning and transmission electron microscopy. Within the tegument numerous vacuoles were formed that released their contents to the exterior and finally caused destruction of the tegument. Proglottides of the central or posterior strobilar portions were never damaged. Larvae of T. taeniaeformis (cysticerci) and E. multilocularis (alveolar cysts) were studied employing the same methods both after in vitro exposure to and after in vivo treatment of their hosts with praziquantel. Strobilocerci of T. taeniaeformis developed identical tegumental lesions after contact with praziquantel whether incubated in vitro or treated in vitro. The wall of the bladder containing the larva remained unaffected. Evaginated protoscolices of E. multilocularis were damaged by in vitro contact with praziquantel while invaginated protoscolices remained intact. After in vivo exposure there were some fully developed evaginated and damaged protoscolices whereas all invaginated protoscolices and the cyst wall with its germinative layer were unaffected.