Hymenolapis diminuta

• Hymenolepis diminuta

  Rat Tapeworm

  
• Hymenolepis diminuta

  • Cosmopolitan parasite primarily of rats
  • Intermediate host is always required (unlike H. nana)
  • Intermediate host: Rat flea
  • Definitive host: Humans, rats
  • Infective stage: Cysticercoid larva
  • Diagnostic stage: Gravid segments in stool
  • Autoinfection: NO

  
• Adult Hymenolepis diminuta

  • Larger than H. nana
  • Scolex has rudimentary, unarmed rostellum and 4 suckers
  • Mature proglottids are broader than they are long, have 3 ovoid testes and 1 ovary, and have unilateral genital pores
  • Gravid proglottid is filled with eggs

  
• Hymenolepis diminuta ova

  • Circular, bile-stained (unlike H. nana that is colorless)
  • Oncosphere is enclosed in an inner membrane with bipolar thickenings but NOT bipolar filaments
  • Hooklets are in a fan-like arrangement
• Life cycle of Hymenolepis diminuta

  1. Definitive hosts release embryonated eggs through feces

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

  3. Definitive hosts acquire the infection by ingesting affected arthropods

  4. Cysticercoid matures into adult H. diminuta, becomes gravid, and releases eggs in the stool

  
• Pathogenesis and Clinical Manifestations

  Infection is usually light, life span of H. diminuta in humans is short
• Diagnosis

  Identification of egg, scolex if expelled (no longer necessary to recover scolex since species can be differentiated by ova)
• Treatment

  Drug of choice: Praziquantel
• Eggs of Hymenolepis diminuta are passed out in the feces of the infected definitive host (rodents, man)

  
• Life cycle of Hymenolepis diminuta (continued)

  1. Mature eggs are ingested by an intermediate host (various arthropod adults or larvae)

  2. Oncospheres are released from the eggs and penetrate the intestinal wall of the host, developing into cysticercoid larvae

  3. Cysticercoid larvae persist through the arthropod's morphogenesis to adulthood

  4. H. diminuta infection is acquired by the mammalian host after ingestion of an intermediate host carrying the cysticercoid larvae

  5. After ingestion, the tissue of the infected arthropod is digested releasing the cysticercoid larvae in the stomach and small intestine

  6. Eversion of the scoleces occurs shortly after the cysticercoid larvae are released

  7. Using the 4 suckers, the parasite attaches to the small intestine wall

  8. Maturation of the parasites occurs within 20 days and the adult worms can reach an average of 30 cm in length

  9. Eggs are released in the small intestine from gravid proglottids that disintegrate after breaking off from the adult worms

  10. The eggs are expelled to the environment in the mammalian host's feces