Hymenolepis nana, a tiny intestinal tapeworm, is the most common human cestode; infection is treated with praziquantel.

Hymenolepis 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 in conditions of poverty and poor hygiene, particularly when fleas are present.

H. nana has 3 modes of infection:

• Indirect 2-host cycle: Rodents are the primary definitive hosts, and grain beetles, fleas, or other insects feed on contaminated rodent droppings as intermediate hosts; humans can become infected by ingesting parasitized insects.
• Human-to-human oral-anal cycle: Eggs are passed from one human to another or recycle externally in a single host.
• Internal autoinfection: 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 cause 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 adult humans living in endemic areas.

Diagnosis is made by finding eggs in stool samples.

Treatment

Praziquantel 25 mg/kg po once is the treatment of choice.

Last full review/revision December 2009 by Richard D. Pearson, MD