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Chapter 143 : Cestodes
Four species of cestode tapeworms inhabit the human intestine: Diphyllobothrium latum, Taenia saginata, Taenia solium, and Hymenolepis nana. Rarer larval cestode infections affecting humans include coenurosis (Taenia multiceps), sparganosis (Spirometra mansonoides), and cysticercosis by Taenia crassiceps. Eggs can be easily seen by microscopical examination of stools. Eggs should be reported as Taenia sp. because direct observation does not confirm the species. T. solium taeniasis and cysticercosis are highly endemic to all parts of the developing world where pigs are raised as a food source. The infection is now also increasingly diagnosed in industrialized countries due to immigration of tapeworm carriers from zones of endemicity. H. nana is the smallest of the intestinal tapeworms of humans and also the most common tapeworm infection throughout the world. H. nana is normally a parasite of mice, and its life cycle characteristically involves a beetle as intermediate host. In humans, transmission is usually accomplished by direct ingestion of infective eggs containing oncospheres. Diagnosis of the infection rests on finding the spherical eggs in feces by microscopy. Eggs are characteristic and should be reported as H. nana. Beside physical examination, diagnosis usually is based on imaging techniques including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) supported by serology. Taenia multiceps and Taenia serialis have canids as definitive hosts and sheep as their normal intermediate host, harboring the larvae or coenurus. Diagnosis is based on pathological demonstration of the typical larval membrane and multiple scolices.