page_title: Hymenolepiasis
section_title: Causes
hierarchical_section_title: Hymenolepiasis / Causes
context_page_description: Hymenolepiasis is infestation by one of two species of tapeworm: Hymenolepis nana or H. diminuta. Alternative names are dwarf tapeworm infection and rat tapeworm infection. The disease is a type of helminthiasis which is classified as a neglected tropical disease.
context_section_description: Hymenolepis worms live in the intestines of rats and are common in warm climates, and are generally found in the feces of rats, which are consumed by their secondary hosts—beetles. The worms mature into a life form referred to as a "cysticercoid" in the insect;  in H. nana, the insect is always a beetle.
  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 lifecycle to be completed in the bowel, so infection can persist for years if left untreated.
  H. nana infections are much more common than H. 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.  When this happens, H. nana oncosphere larvae encyst in the intestinal wall and develop into cysticercoids and then adults.  These 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.  H. nana infections can grow worse over time because, unlike in most tapeworms, H. nana eggs can hatch and develop without ever leaving the definitive host.
caption: Lifecycle of H. nana