Hymenolepis nana

Background

• Cyclophyllidean cestode within the genus Hymenolepis known as the dwarf tapeworm, closely related to Hymenolepis diminuta, the rate tapeworm

Life Cycle

• Eggs are passed in stool, and cannot survive more than 10 days in the environment
• Eggs are ingested by an intermediate host, typically insects including beetles and fleas, where the eggs develops into cysticercoids
• The intermediate host with cysticercoids gets eaten by a rat (or a human), where it develops into an adult worm in the small intestine
• However, if eggs are directly ingested by a human (from contaminated food or water or hands), the oncospheres contained in the eggs can hatch and develop into cysticercoid larvae within the human before developing into the adult worm
• Can cause internal autoinfection in the host

Epidemiology

• Distributed worldwide, and likely to most common tapeworm worldwide
• Acquired by exposure to contaminated food or water
• Can be spread person-to-person, with the human acting as intermediate and definitive host
• More common in children and institutionalized adults and in areas with poor sanitation
• Highly endemic areas include Asia, southern and eastern Europe, Central and South America, and Africa
• In North America, most cases are travel-related

Clinical Manifestations

• Infections are mostly asymptomatic
• Typical symptoms would be mild abdominal discomfort
• Heavy burden of infection (mostly in children) can cause anorexia, abdominal pain or cramps, diarrhea, weakness, and headaches or dizziness
• Dwarf tapeworms can grow 15 to 40 mm in length (compared to 20 to 60 cm for the rat tapeworm)

Diagnosis

• Diagnosis is made by detecting eggs in stool (30x47 µm eggs with characteristic double membrane)

Management

• First-line: praziquantel 25 mg/kg p.o. once
• Second-line:
  • Niclosamide 2 g p.o. daily for 7 days
  • Nitazoxanide 500 mg p.o. twice daily for 3 days