In the United States, H.nana is considered to be the most common tapeworm recovered, especially in the southeast part of the country.It is also known that the tropical and subtropical climates of the world harbor this parasite.Individuals residing in close neighborhoods, such as in institutional settings, as well as children attending preschool or day care centres, are at a particularly high risk of H.Nana. In addition to infective eggs from contaminated human feces, stool from contaminated rodents can also be a source of infection.
Morphology of Hymenolepis nana
The slightly round to oval egg of Hymenolepis nana typically measures 45 by 38 μm.The central hexacanth embryo is fitted with three standard pairs of hooklet.A shell full of polar thicknesses protects the embryo.Numerous polar filaments originate from the polar thickenings, which help to distinguish it from the egg of Hymenolepis diminuta in addition to its size.A colorless embryo forms the outermost layer of eggs
Like cestode scolices, the Hymenolepis nana scolex contains four suckers. The presence of a short rostellum with a row of hooks helps to distinguish it from Hymenolepis diminuta, which does not have any hooks.
The mature and gravid proglottids of Hymenolepis nana are similar to those of Hymenolepis diminuta in size and appearance. A short description can be found in the section Hymenolepis diminuta proglottid morphology.
Life Cycle of Hymenolepis nana
The consumption of an infective egg triggers human infection with Hymenolepis nana.Cysticercoid larvae develop in the intestine.With further maturation, the scolex emerges and adheres to the intestinal mucosa (parasite intestinal).The resulting adult worm is located in the intestine where it can reproduce itself.Numerous eggs are released through the disintegration of gravid proglottids.At this point, a resulting egg can take one of two paths.The egg can be excreted from the body via the stool or initiate an autoinfection.An egg released into the external environment is in the infection stage.No intermediate host is required to complete the cycle.Such an egg, when taken up by a new human host, initiates a new cycle.An egg that remains inside the human being can hatch in the gastrointestinal tract and develop into an adult that never leaves the human host and thus initiates a new cycle.
As mentioned above, Hymenolepis nana does not require an intermediate host to complete its life cycle.However, this parasite may be present in a number of other animal transport hosts, such as fleas, beetles, rats and house mice.It is interesting to note that the cysticercoid larval stage can develop in these hosts when this happens; such hosts are contagious to both humans and rodents.
Clinical symptoms of Hymenolepiasis
Light infections with H. nana typically remains asymptomatic
Hymenolepiasis(Dwarf Tapeworm Disease)
Persons with heavy H. Nana infections often cause gastrointestinal symptoms such as abdominal pain, loss of appetite, diarrhea, dizziness and headaches.
Laboratory Diagnosis of Hymenolepiasis
Laboratory diagnostics from H. nana is achieved by the examination of stool samples for the characteristic eggs.
Treatment of Hymenolepiasis
Praziquantel is considered the treatment of choice for infections with H. nana. Niclosamide is also known to be an effective alternative drug, but it is not yet readily available in the United States.
Prevention and Control of Hymenolepiasis
Proper hygiene and cleanliness are essential to prevent the spread of H. nana. Control of the transport host population and avoidance of contact with potentially infected rodent faeces are also preventive and control measures to stop the spread of the parasite.
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