Hymenolepis nana, a tiny intestinal tapeworm, is one of the most common human cestodes; the life cycle does not require an intermediate host. Infection is treated with praziquantel or niclosamide.
H. nana is only 15 to 40 mm long. It differs from other tapeworm because 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 weeks).
H. nana is more frequent in populations, particularly children, 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 second generation without ever exiting the host. Autoinfection can result in large numbers of worms and symptoms.
Symptoms and Signs of Hymenolepis nana Infection
Infections are often asymptomatic, but heavy infections may cause crampy abdominal pain, diarrhea, anorexia, pruritis ani, and nonspecific systemic symptoms. On occasion H. nana is misdiagnosed as pinworm infection.
Diagnosis of Hymenolepis nana Infection
Microscopic examination of stool for ova and proglottids
Diagnosis is made by finding eggs in stool samples.
Treatment of Hymenolepis nana Infection
Praziquantel
Alternatively, nitazoxanide or, outside the United States, niclosamide
The treatment of choice for H. nana infection is
Praziquantel 25 mg/kg orally once
Alternatives include nitazoxanide and niclosamide (not available in the United States).
For nitazoxanide, dosage is
For patients > 11 years: 500 mg orally 2 times a day for 3 days
For children aged 4 to 11 years: 200 mg orally 2 times a day for 3 days
For children aged 1 to 4 years: 100 mg orally 2 times a day for 3 days
For niclosamide, dosage is
For adults: 2 g orally once/day for 7 days
For children > 34 kg: 1.5 g in a single dose on day 1, then 1 g once/day for 6 days
For children 11 to 34 kg: 1 g in a single dose on day 1, then 500 mg once/day for 6 days
A stool sample should be repeated one month after therapy is completed to verify cure.
See also Centers for Disease Control and Prevention: Parasites - Hymenolepiasis (also known as Hymenolepis nana infection).
