Hymenolepis nana Hymenolepis
Hymenolepis nana adult scolex with four
suckers and rostellum.
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%.
Human Biology 103
D. Scott Smith, MD, instructor