Hymenolepis nana

Background

• 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
• 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

Epidemiology

• Distributed worldwide
• More common in children and institutionalized adults

Clinical Manifestations

• Infections are mostly asymptomatic
• Heavy burden of infection can cause anorexia, abdominal pain, diarrhea, weakness, and headaches
• Dwarf tapeworms can grow 15 to 40 mm in length (compared to 20 to 60 cm for the rat tapeworm)