Background Hymenolepis nana, also known's as the ‘dwarf tapeworm,’ is the smallest tapeworm. Discovered by Bilharz in Cairo in 1851 It was first identified as human parasite by Von Siebold in 1852 Most common cestodes of human in the world, especially among children
Geographic Distribution Hymenolepis nana has a wide distribution, it is more prevalent in warm areas. It exists in Africa, Mexico, South America, South east Asia and parts of Eastern Europe
Morphology Adult worm is 10-45 mm long and 0.5-1 mm wide, with 100- 200 segments The eggs (30-50 ㎛ ) are oval to spherical and almost colorless. have a 6-hooked oncospheres inside the shells Scolex is small, 0.3 mm in diameter. It has four suckers Proglottids are 0.2-0.3 mm long and 0.8-0.9 mm wide and has both female and male reproductive organs
Life Cycle in words Eggs of Hymenolepis nana are immediately infective when passed with the stool and cannot survive more than 10 days in the external environment. When eggs are ingested by an arthropod intermediate host, they develop into cysticercoids, which can infect humans or rodents upon ingestion and develop into adults in the small intestine. A morphologically identical variant, H. nana var. fraterna, infects rodents and uses arthropods as intermediate hosts. When eggs are ingested (in contaminated food or water or from hands contaminated with feces), the oncospheres contained in the eggs are released. The oncospheres penetrate the intestinal villus and develop into cysticercoid larvae. Upon rupture of the villus, the cysticercoids return to the intestinal lumen, evaginate their scoleces, attach to the intestinal mucosa and develop into adults that reside in the ileal portion of the small intestine producing gravid proglottids. Eggs are passed in the stool when released from proglottids through its genital atrium or when proglottids disintegrate in the small intestine. An alternate mode of infection consists of internal autoinfection, where the eggs release their hexacanth embryo, which penetrates the villus continuing the infective cycle without passage through the external environment. The life span of adult worms is 4 to 6 weeks, but internal autoinfection allows the infection to persist for years.
Pathogenesis Gastrointestinal pain Diarrhoea, Vomiting Loss of appetite and loss of weight. The infection may also cause nervousness and insomnia.
Treatment Diagnosis Praziquantel or surgery If praziquantel is not available, niclosamide or albendazole can be used instead Finding eggs in stool specimens. Adult worm can be identified during endoscopic examination.
Control Observing personal hygiene Good sanitation Destruction of rats and mice Treating of infected persons.
Pop Quiz What’s another name for Hymenolepis nana? What year was this parasite discovered and where? In the life cycle does H nana require intermediate host to complete its life stages? What can happen if eggs remain in the intestine? What is one way that you can control this parasite?