Hymenolepis infection

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Hymenolepis infection (hymenolepiasis) is infestation by one of two species of tapeworm, Hymenolepis nana or Hymenolepis diminuta.

Hymenolepis infection (hymenolepiasis) is caused by one of the two species of tapeworm, Hymenolepis nana or Hymenolepis diminuta. Hymenolepis nana infections are much more common than Hymenolepis diminuta infections in humans, because in addition to being spread by insects, the disease can be spread directly from person to person by eggs in feces. Humans and other animals become infected when they intentionally or unintentionally eat material contaminated by insects. In an infected person, it is possible for the worm’s entire life-cycle to be completed in the bowel, so infection can persist for years.

Most people who are infected do not have any symptoms. Those who have symptoms may experience nausea, weakness, loss of appetite, diarrhea, and abdominal pain. Young children, especially those with a heavy infection, may develop a headache, itchy bottom, or have difficulty sleeping. Sometimes infection is misdiagnosed as a pinworm infection. Contrary to popular belief, a tapeworm infection does not generally cause weight loss. You cannot feel the tapeworm inside your body.

Examination of the stool for eggs and parasites confirms the diagnosis. Concentration techniques and repeated examinations will increase the likelihood of detecting light infections. The eggs and proglottids of H. nana are smaller than H. diminuta. Proglottids of both are relatively wide and have three testes.

A prescription drug called praziquantel is given. The medication causes the tapeworm to dissolve within the intestines. Praziquantel is generally well tolerated. Sometimes more than one treatment is necessary.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Hymenolepiasis is caused by two cestodes (tapeworm) species, Hymenolepis nana (the dwarf tapeworm, adults measuring 15 to 40 mm in length) and Hymenolepis dimnuta (the rat tapeworm, adults measuring 20 to 60 cm in length). Hymenolepis diminuta is a cestode of rodents infrequently seen in humans and frequently found in rodents.

• Hymenolepis nana

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 (various species of beetles and fleas may serve as intermediate hosts), 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 (hexacanth larvae) 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.

• Hymenolepis diminuta

Eggs of Hymenolepis diminuta are passed out in the feces of the infected definitive host (rodents, man). The mature eggs are ingested by an intermediate host (various arthropod adults or larvae), and oncospheres are released from the eggs and penetrate the intestinal wall of the host, which develop into cysticercoid larvae. Species from the genus Tribolium are common intermediate hosts for H. diminuta. The cysticercoid larvae persist through the arthropod’s morphogenesis to adulthood. H. diminuta infection is acquired by the mammalian host after ingestion of an intermediate host carrying the cysticercoid larvae . Humans can be accidentally infected through the ingestion of insects in precooked cereals, or other food items, and directly from the environment (e.g., oral exploration of the environment by children). After ingestion, the tissue of the infected arthropod is digested releasing the cysticercoid larvae in the stomach and small intestine. Eversion of the scoleces occurs shortly after the cysticercoid larvae are released. Using the four suckers on the scolex, the parasite attaches to the small intestine wall. Maturation of the parasites occurs within 20 days and the adult worms can reach an average of 30 cm in length. Eggs are released in the small intestine from gravid proglottids that disintegrate after breaking off from the adult worms. The eggs are expelled to the environment in the mammalian host’s feces.

‘’H. diminuta’’ has an effective mechanism for interspecies transfection. Beetles are more likely to ingest rat droppings that are infected with tapeworm eggs. These droppings produce a fragrance (although it is not known if it is produced specifically by the eggs or the droppings) that attracts the beetle. ‘’H. diminuta’’ also sterilizes its beetle host. This is so the beetle does not waste energy in its reproductive system, allowing ‘’H. diminuta’’ to further exploit the beetle’s metabolic resources. ^[1]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Hymenolepis infection (hymenolepiasis) is caused by one of the two species of tapeworm, Hymenolepis nana or Hymenolepis diminuta. Hymenolepis nana infections are much more common than Hymenolepis diminuta infections in humans, because in addition to being spread by insects, the disease can be spread directly from person to person by eggs in feces. Humans and other animals become infected when they intentionally or unintentionally eat material contaminated by insects. In an infected person, it is possible for the worm’s entire life-cycle to be completed in the bowel, so infection can persist for years.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Furqan M M. M.B.B.S[2]

Hymenolepiasis must be differentiated from tapeworm infections like diphyllobothriasis, taeniasis, and schistosomiasis.

Hymenolepiasis must be differentiated from tapeworm infections like diphyllobothriasis, taeniasis, and schistosomiasis.^[1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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• In temperate areas its incidence is higher in children and institutionalized groups.

• Hymenolepis infections were previously common in the southeastern USA, and have been described in crowded environments and individuals confined to institutions. However, the disease occurs throughout the world.
• Hymenolepis nana is the most common cause of all cestode infections, and is encountered worldwide.
• Hymenolepis diminuta, while less frequent, has been reported from various areas of the world.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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• Abdominal discomfort
• Dehydration from prolonged diarrhea

Infection with the dwarf tapeworm is generally not serious. However, prolonged infection can lead to more severe symptoms; therefore, medical attention is needed to eliminate the tapeworm. Cure rates are extremely good with modern treatments.