Hymenolepiasis

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Hymenolepiasis is infestation by one of two species of tapeworm:

Alternative names are:

Hymenolepis worms live in the intestines of rats and are common in warm climates. Hymenolepis is generally found in the feces of rats which is consumed by its 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 life-cycle to be completed in the bowel, so infection can persist for years if left untreated. 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. 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.

A study in Connecticut found that one third of rats sold in pet stores were infected with H. nana and concluded that these and other rodents sold in pet stores pose a potential threat to public health.

The risk of human infection from ‘’H. dimunuta’’ is very low, since its main host is the rat. Also known as the “rat tapeworm”, H. diminuta adults live and mate in the bowels of rats. Eggs of H. diminuta are excreted by the rats as droppings, which are frequently consumed by beetles. Once inside the beetle, the eggs mature into a “cysticercoid”. The juvenile tapeworms claw their way out of the beetle gut into the circulatory system by means of their three pairs of hooks. There, they wait for a rat to ingest the host beetle, where they mature to adult form, lay eggs and restart the entire cycle. [1]

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, if female. 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]

Hymenolepis nana is a tapeworm, belonging to the class Cestoidea, phylum platyhelmenthes.

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