Cestodes

Cestodes are segmented flatworms and have as their key characteristic a flattened body composed of the head or scolex (bearing the fixation organs-suckers, hooks, and bothria), the neck (where the cellular reproduction occurs, to form the strobila), and the strobila, formed by numerous segments or proglottids. Cestode tapeworms live in the lumen of the small intestine with the head or scolex as the only fixation organ, attached to the mucosa, so they develop cephalic fixation organs like hooks, suckers, or shallow grooves as longitudinal suction sulci (bothria). They absorb nutrients from the host’s intestine both at the head and through their tegument, and they thus also develop a specialized tegument. Four species of cestode tapeworms inhabit the human intestine with frequency: Diphyllobothrium latum, Taenia saginata, Taenia solium, and Hymenolepis nana. They differ widely in size, intermediate host, and other characteristics, from the 12-m D. latum to the 3-cm H. nana. In addition, a number of cestode larvae can produce human disease if infective tapeworm eggs are ingested, mainly cysticercosis (Taenia solium), cystic hydatid disease (Echinococcus granulosus), and alveolar hydatid disease (Echinococccus multilocularis). Rarer larval cestode infections affecting humans include coenurosis (Taenia multiceps), sparganosis (Spirometra mansonoides), and cysticercosis by Taenia crassiceps. Tapeworms and especially tapeworm larval infections still represent an important cause of morbidity and mortality, not only in most underdeveloped countries but also in industrialized countries, particularly in rural areas or among immigrants from areas of endemicity.