Contents

Search

Hymenolepis nana (dwarf tapeworm)

Epidemiology: 1) world-wide distribution 2) most frequently recovered cestode species in USA 3) common parasite in mice 4) humans may acquire infection by ingestion of a) infectious eggs 1] passed directly person to person, generally children 2] grains contaminated with rodent feces b) intermediate hosts (generally grain beetles) containing infectious cysticercoid larva c) fleas can also serve as intermediate hosts [3] Pathology: 1) ingested eggs hatch in intestine 2) embryos penetrate the mucosa where they mature as cysticercoid larva 3) cysticercoid emerge from the mucosa, attach to the intestinal wall & develop into adult tapeworms in 2-3 weeks 4) adults may attain length of 4 cm 5) scolex has armed rostellum 6) proglottids have genital pores on the same side of strobila 7) autoinfection may occur in some individuals a) released eggs hatch prior to leaving the intestine b) they penetrate the mucosal wall to reinitiate the developmental cycle c) this mechanism may be responsible for occasional infections with large tapeworm loads Clinical manifestations: 1) may be asymptomatic 2) abdominal pain, diarrhea, anorexia, irritability may develop in patients with large tapeworm loads Laboratory: 1) diagnosis is made by recovery of eggs in the feces a) oval, thin-shelled & colorless b) 30-47 um in diameter c) contain a centrally located 6-hooked embryo (oncosphere) separated from the outer shell by a clear space 2) embryo displays 2 polar thickenings from which thin filaments arise & extend into the clear space between the embryo & the outer shell 3) strobila may occasionally be recovered from feces Complications: - malignant transformation of H nana invading human host as metastatic cancer in an HIV1 infected patient [4] Management: 1) praziquantel 25 mg/kg PO once a) treatment of choice b) active against both adult worm & cysticercoids in intestinal villi 2) niclosamide a) 2 g PO day 1, then 1 g PO QD for 6 days b) active against both adult worm; ineffective against cysticercoids 3) personal hygiene & improved sanitation

Related

cysticercoid flea (Siphonaptera)-borne infection hexacanth (oncosphere) proglottid rostellum scolex strobila

General

Hymenolepis

Properties

KINGDOM: animal PHYLUM: helminth

References

  1. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 1288-89
  2. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 933
  3. Wkipedii: Hymenolepis nana http://en.wikipedia.org/wiki/Hymenolepis_nana
  4. Muehlenbachs A et al Malignant Transformation of Hymenolepis nana in a Human Host. N Engl J Med 2015; 373:1845-1852. November 5, 2015 PMID: 26535513 http://www.nejm.org/doi/full/10.1056/NEJMoa1505892
  5. Grimm L What's Eating You: 12 Common Intestinal Parasites. Medscape. November 25, 2019 https://reference.medscape.com/slideshow/intestinal-parasites-6010996