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Hymenolepis nana, a small intestinal
tapeworm, is the most common human cestode; infection is treated
with praziquantel.
H. nana is only 15 to 40 mm long. It requires only one host but can also cycle through two. Its larvae migrate only within the gut wall, and its life span is relatively short (4 to 6 wk). H. nana is more frequent in populations living under conditions of poverty and poor hygiene, particularly when fleas are present.
H. nana has 3 modes of infection: (1) an indirect 2-host cycle involving rodents as primary definitive hosts and grain beetles, fleas, or other insects that feed on contaminated rodent droppings as intermediate hosts; (2) an oral-anal cycle in which eggs are passed from one human to another or recycle externally in a single host; and (3) internal autoinfection, whereby eggs hatch within the gut and initiate a 2nd generation without ever exiting the host. Autoinfection can result in massive numbers of worms, which can produce nausea, vomiting, diarrhea, abdominal pain, weight loss, and nonspecific systemic symptoms. The pronounced cellular and humoral response to the tissue phase of H. nana infection probably provides some protection for adults living in endemic areas.
Diagnosis is made by finding eggs in stool samples. Praziquantel 25 mg/kg po once is the treatment of choice.
Last full review/revision November 2005
Content last modified November 2005
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