. Hymenolepiasis

Hymenolepiasis


 

Héctor H. García and Robert H. Gilman


 

Infection with Hymenolepis nana, the dwarf tapeworm, is the most common tapeworm infection in the world. H nana is found in 0.4% of fecal specimens submitted to state laboratories in the United States. Infections occur most frequently in warm countries. It is especially prevalent in the southern part of the former Soviet Union, the Mediterranean, the Indian subcontinent, and South America. Children are more commonly infected than adults, and high prevalence rates have been reported in institutionalized children because of fecal-oral transmission.1


In the usual cycle, H nana is passed between rodents as definitive host and beetles as intermediate hosts. H nana is unique among tapeworms, because humans can serve as both intermediate and definitive hosts and can close the cycle without the need for an animal intermediate host. This leads to human infection being directly acquired (from another human definitive host), thus contributing to its high prevalence.


The adult tapeworm measures 2 to 4 cm in length. It attaches to the mucosa of the small intestine by a scolex that has 4 circular suckers and a retractable structure called a rostellum. Eggs passed in the feces are immediately infectious for another human or for the original host (autoinfection). Ingested eggs hatch in the small intestine. The embryos penetrate the villi and transform into larval cysticercoids. After 4 or 5 days, the new adult tapeworms emerge from the tissue and attach to the intestinal mucosa. Egg production by the new worms begins about 2 to 4 weeks after infection. Eggs released from gravid proglottids in the intestine may hatch and cause internal autoinfection, producing hundreds or thousands of adult tapeworms in a single host.1,2



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Jan 7, 2017 | Posted by in PEDIATRICS | Comments Off on . Hymenolepiasis

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