Hymenolapis nana

• Hymenolepis nana

  Dwarf tapeworm
• Hymenolepis nana

  • Smallest tapeworm infecting humans
  • Only human tapeworm that completes its entire life cycle in a single host
  • Human harbor both adult and larval stages
  • Does not require obligatory intermediate host

  
• Habitat

  Small intestine, usually ileum
• Diagnostic stage

  Gravid proglottid
• Infective stage

  Cysticercoid larva

  
• Definitive hosts

  • Humans
  • Rats
• Intermediate hosts

  • Rice and flour beetle
• Autoinfection: YES
• Scolex

  • Subglobular with four cup-shaped suckers
  • Retractable rostellum armed with single row of 20 – 30 Y-shaped hooklets
• Neck

  • Long and slender
• Strobila


  • 175 – 220 segments
  • Anterior proglottids: short
  • Posterior proglottids: broader than long
  • Lateral genital pore
• Mature proglottid

  • 3 ovoid testes
  • 1 ovary
• Gravid proglottids

  • Testes and ovary disappear
  • Uterus hollows out and filled with eggs
  • Gravid segments separate from strobila and disintegrate as they pass out of the intestines → releasing eggs
• Gravid proglottids are NOT demonstrated in feces as they are broken down in the intestines.
• Ova

  • Spherical, colorless or clay-colored
  • Not stained with bile
  • Oncosphere: thin outer membrane and thick inner membrane with conspicuous bipolar thickenings, from each of which arise 4 – 8 hair-like polar filaments
  • Eggs die immediately once passed
• Eggs can be differentiated from H. diminuta; H. nana is colorless, H. nana has bipolar thickening – characteristics that is not present in H. diminuta
• Life Cycle of Hymenolepis nana

  1. Definitive hosts release embryonated eggs through the feces

  2. Insects, which are the intermediate hosts, ingest the embryonated eggs and are infected. The egg hatches and the (oncosphere →) cysticercoid develops inside the intermediate host.

  3. Definitive hosts acquire the infection when they ingest affected arthropods

  4. Cysticercoid matures into adult H. nana and becomes gravid, releasing eggs by apolysis. Eggs are passed in the stool and the cycle continues

  
• Monoxenous life cycle

  1. Adult H. nana shed proglottids in the small intestine releasing embryonated eggs

  2. Eggs hatch to release oncosphere (hexacanth) which penetrates the intestinal lumen to mature into cysticercoid larvae

  3. Cysticercoid larvae returns to the intestinal lumen to mature into adult H. nana and the cycle continues.
• Direct Development

  1. Host ingest the egg in the proglottid which hatch in the duodenum. The liberated embryo penetrate the villi and develop into cysticercoid larva

  2. After 4 – 5 days, larva breaks out of villi and develops into adult
• Indirect Development

  1. Via ingestion of infected rice and flour beetles (Tenebrio)

  2. Via ingestion of fomites, water, or food contaminated with the larvae
• Light Worm Burden

  • Asymptomatic
• Manifestations

  • Headache, dizziness, anorexia, pruritus of nose and anus, diarrhea, vomiting, abdominal pain, pallor, weight loss
  • Non-specific
• Heavy Infection

  • Enteritis due to necrosis and desquamation of intestinal epithelial cells
• With time, immune system will clear the infection → infection will resolve spontaneously. Possible to clear without anti-helminthics
• Diagnosis

  Demonstration of the characteristic eggs in the patient's stool
• Generally, proglottids are NOT recovered in the stool because they undergo degeneration prior to passage with stools
• Treatment

  Drug of Choice: Praziquantel
• Successful treatment

  Negative stool after one month of treatment