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Hymenolepis nana                    Hymenolepis diminuta

Dwarf tapeworm                        Rat tapeworm

        

Hymenolepis nana adult scolex with four suckers and rostellum.

Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Genus: Hymenolepis


Hymenolepis
species are tapeworms occurring throughout the world in temperate to tropical conditions of poor sanitation. Of the over 400 species, all are found in higher vertebrates, while its principal definitive hosts are rodents. They can infect humans, when an infected arthropod containing a cysercoid from the metacestode stage is accidentally ingested and arrives in the small intestine. The two most problematic for humans are Hymenolepis nana and Hymenolepis diminuta. Also referred to as Vampirolepsis nana, H. nana is mainly a parasite of humans, but found more commonly in mice, and has been widely used as a model system for the study of cestode/tapeworm biology. The most commonly researched species of tapeworms, H. diminuta is mainly a parasite of rats, and has been reported in humans on rare occasion. Distinguishing between these species is done by microscopy of their eggs when passed through the feces.


In humans, infections with Hymenolepis nana are much more common than infections with Hymenolepis diminuta. H. nana is the most common cause of all cestode infections and is encountered worldwide. A relatively high prevalence of H. nana has been reported in surveys conducted in Europe and Latin America. In temperate areas, its incidence is higher in children and institutionalized groups. H. diminuta is less frequent, but has been reported from various areas of the world. parasitization rate ranging between .0001 and 5.5%.

 

Marie Holzapfel
Parasites and Pestilence
Human Biology 103
Spring, 2002
D. Scott Smith, MD, instructor