Hymenolepis nana can be found throughout the world, but is usually most common in temperate zones. It is the most common cestode of humans and is found wherever there are human inhabitants. (Roberts and Janovy Jr., 2000)
The adults of the dwarf tapeworm are 25 to 40 mm in length and 1 mm in width (Lapage, 1951). This tapeworm is transparent, and has a long slender neck with segments wider than they are long. The genital pores are unilateral, or on the side of the segment. Each segment contains a single proglottid, which contains a single set of reproductive organs. On the scolex, a retractable rostellum with 20 to 30 hooks can be found (Roberts and Janovy, 2000). The scolex also has four suckers, or a tetrad.
The cysticercoid has a tail, which is made of longitudinal fibers and is spade shaped with the rest of the worm still inside the cyst (Roberts and Janovy, 2000). The eggs of H. nana are round or slightly oval at about 40-60 micrometers X 30-50 micrometers with 4-8 polar filaments spread out between the inner and outer membranes (Ghaffar, 2001). Unlike other taeniid eggs, the eggs of H. nana do not have a striated appearance (Roberts and Janovy, 2000). (Ghaffar, 2001; Lapage, 1951; Roberts and Janovy Jr., 2000)
A gravid proglottid contains fertilized eggs, which are sometimes expelled with the feces (Cameron, 1956). However, most of the time, the egg settles in the microvilli of the small intestine, hatch, and the larvae can develop to sexual maturity without ever leaving the host (Olsen, 1974). An intermediate host is optional; H. nana can go through its life cycle with only one host or can also go through the normal two-host cycle (Roberts and Janovy, 2000). The life cycle can be described as: 1)eggs are ingested by definitive hosts 2)eggs hatch in the duodenum, releasing oncospheres and lie in the lymph channels of the villi 3)oncospheres develops into a cysticercoid, which has a tail and a well formed scolex, and it attaches to the small intestine and matures into an adult 4a)gravid proglottids then release and pass out through feces along with eggs 4b)or eggs can hatch and infect original host and start cycle over or 5)eggs can be ingested by insects or rodents (Roberts and Janovy, 2000). (Cameron, 1956; Olsen, 1974; Roberts and Janovy Jr., 2000)
Hymenolepis nana, like all tapeworms, contain both male and female reproductive structures in each proglottid (Roberts and Janovy, 2000). This means that the dwarf tapeworm like other tapeworms is hermaphroditic (Cameron, 1956). Each segment contains 3 testes and a single ovary. When a proglottid becomes old and unable to absorb any more nutrition, it is released and is passed through the host's digestive tract (Roberts and Janovy, 2000). This gravid proglottid contains the fertilized eggs, which are sometimes expelled with the feces (Cameron, 1956). However, most of the time, the egg may also settle in the microvilli of the small intestine, hatch, and the larvae can develop to sexual maturity without ever leaving the host (Olsen, 1974). (Cameron, 1956; Olsen, 1974; Roberts and Janovy Jr., 2000)
H. nana does not have a digestive system and each body segment has its own reproductive structures (Roberts and Janovy, 2000). Usually after it is ingested as an egg, it will lodge itself in the intestinal wall and then in five to six days, the cysticercoid emerges into the lumen of the small intestine, sheds it tail and becomes a mature tapeworm (Roberts and Janovy, 2000). (Roberts and Janovy Jr., 2000)
Cestodes in general have sensory organs in the scolex, which are attached to longitudinal nerves extending down the body. The nerves are attached to organs and the cestodes can detect tactile stimulation. (Brusca and Brusca, 2003)
The dwarf tapeworm like all other tapeworms lacks a digestive system and feeds by absorption on nutrients in the intestinal lumen (Cameron, 1956). They have non-specific carbohydrate requirements and it seems like they will absorb whatever is being passed through the intestine at that time (Cameron, 1956). When it becomes an adult, it will attach to the intestinal walls with its suckers and toothed rostellum and have its segments reaching out into the intestinal space to absorb food (Roberts and Janovy, 2000). (Cameron, 1956; Roberts and Janovy Jr., 2000)
These animals are probably not preyed on directly but are ingested. Egg and larval mortality are high due to not reaching a suitable host.
An intermediate host is optional; H. nana can go through its life cycle with only one host or can also go through the normal two-host cycle (Roberts and Janovy, 2000). Some of the hosts that this tapeworm can be found in are humans, rodents and insects (Roberts and Janovy, 2000). The insect hosts of H. nana could be fleas, flour beetles, and other copraphagous (dung eating) insects. (Olsen, 1974; Roberts and Janovy Jr., 2000)
Hymenolepis nana is the most common cestode parasite of humans in the world (Roberts and Janovy, 2000). It lodges itself in the intestines and absorbs nutrients from the intestinal lumen (Cameron, 1956). In human adults, the tapeworm is more of a nuisance than a health problem, but in small children, many H. nana can be dangerous. Usually it is the larva of this tapeworm that causes the most problem in children (Lapage, 1951). The larva will burrow into the walls of the intestine, if there are enough tapeworms in the child, severe damage can be inflicted. This is done by absorbing all the nutrition from the food the child eats (Lapage, 1951). Usually a single tapeworm will not cause any danger, but in small children, many tapeworms can become a problem (Lapage, 1951). Hymenolepis nana usually will not cause deaths unless in extreme circumstances and usually in young children or in people who have weakened immune systems. In some parts of the world, individuals that are heavily infected are a result of internal autoinfection (Olsen, 1974). (Cameron, 1956; Lapage, 1951; Olsen, 1974; Roberts and Janovy Jr., 2000)
Renee Sherman Mulcrone (editor).
Wilson Long (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
living in landscapes dominated by human agriculture.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).
either directly causes, or indirectly transmits, a disease to a domestic animal
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
found in the oriental region of the world. In other words, India and southeast Asia.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
scrub forests develop in areas that experience dry seasons.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
living in cities and large towns, landscapes dominated by human structures and activity.
Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..
Cameron, T. 1956. Parasites and Parsitism. NY: John Wiley and Sons, Inc..
Ghaffar, A. 2001. "Cestodes" (On-line). Accessed October 14, 2004 at http://www.med.sc.edu:85/parasitology/cestodes.htm.
Lapage, G. 1951. Parasitic Animals. Great Britain: The University Press.
Ohio State University, 2001. "Hymenolepis nana (Vampirolepsis nana)" (On-line). Parasites and Parasitological Resources. Accessed October 14, 2004 at http://www.biosci.ohio-state.edu/~parasite/hymenolepis_nana.html.
Olsen, O. 1974. Animal Parasites, Third Edition. MD: University Park Press.
Roberts, L., J. Janovy Jr.. 2000. Foundations of Parasitology, Sixth Edition. MA: Mcgraw-Hill Higher Education.