The adult worm lives in the intestine of its host, normally rats but also sometimes dogs and humans. Hymenolepis diminuta passes through the required intermediate arthropod host as a juvenile. Only when the intermediate host is injested by the definitive host will H. diminuta mature. The intermediate arthropod host is normally a grain beetle, and injestion of the intermediate host into the definative host normally occurs in piles of grain, where both rats and beetles live. (Arai, 1980; Pappas, SEP 2000; Shostak and Smyth, AUG 1998; Sturdevant, 1907; Willis and Poulin, 1999)
Adult Hymenolepis diminuta reach 20 to 60 cm, and up to 90 cm . The cestode has a long cylindrical body with 4 suckers and an apical organ at its scolex with no rostellar hooks. Hymenolepis diminuta, along with all cestodes, lacks any trace of a digestive tract, and it absorbs all required substances through its external covering. Posteriorly directed microtriches cover the cestode's tegument, which add to the surface area of the animal and thus to the amount of nutrients it can absorb.
Hymenolepis diminuta, like all other cestodes, has three body sections, a scolex (head), neck, and a strobilus, which is the rest of the cestodes body. The strobilus is divided into many sections called proglottids, each with male and female sexual organs. These are the defining characteristics of cestodes. (Arai, 1980; Deines, et al., JUL 1999; Pappas, SEP 2000; Roberts and Janovy, 2000)
The life cycle of H. diminuta involves rodents (rats primarily) as the definitive host and beetles (flour and grain beetles, Tribolium spp. and Tenebrio spp., respectively) as the intermediate host. The tapeworm's eggs are passed in the rat's feces, and beetles are infected when they eat the eggs; the metacestode stage in the beetle is called a cysticercoid. The rat is infected when it eats an infected beetle. Once the egg is digested by the intermediate host arthropod, the oncosphere, a fully developed larva contained in the egg, is released into the intermediate host. Its function is to migrate to the haemocoel (body cavity) of the insect where it will grow and differentiate into an encapsulated juvenile worm. This stage, the cysticercoid, is dormant and resides in the insect until both are eaten by a foraging rat. Within the definitive hosts' stomach and intestine, the larval worm responds to chemical signals and excysts. It then invades the intestinal lumen, evaginates its scolex, attaches to the intestinal mucosa and develops into an adult.
Once the adult H. diminuta is embedded in the host, it can produce over 250,000 eggs per day. Thus, over a period of slightly over a year, a single tapeworm could produce a hundred million eggs and if all these eggs reached maturity, it would be equal to 20 tons of tapeworm tissue. There is an extremely low chance for each egg to reach reproductive maturity and that is why H. diminuta lays so many eggs. (Andreassen, et al., 1999; Arai, 1980; Ohio State University, 2001; Pappas, et al., 1999; University of Aberdeen, 1997)
Hymenolepis diminuta has both male and female reproductive organs in the same individual. Each segment has one complete set of male and female sex organs. As the segments move toward the posterior end of the strobilus, first the male organs mature, and produce sperm that are stored until the maturation of the ovary. Once the adult H. diminuta is embedded in the host, it can produce over 250,000 eggs per day. Thus, over a period of slightly over a year, a single tapeworm could produce a hundred million eggs and if all these eggs reached maturity, it would be equal to 20 tons of tapeworm tissue. There is an extremely low chance for each egg to reach reproductive maturity and that is why H. diminuta lays so many eggs.
Recent studies have been done on the temperature tolerance of Hymenolepis diminuta eggs. The tapeworm's eggs survived at higher and lower temperatures and for longer periods of time than did adult beetles, indicating that the thermal tolerance of the eggs does not limit the parasite's distribution. (Andreassen, et al., 1999; Arai, 1980; Ohio State University, 2001; Pappas and Barley, APR 1999)
A behavior modification of H. diminuta is the cestode's movement. The cestode has two types of muscle portions in the strobilus, the contractile myofibril and the noncontractile myocyton. The myocytons contain a nucleus, rough endoplasmic reticulum, free ribosomes, a vesicular Golgi apparatus, few mitochondria and abundant glycogen. Lipid is stored in them as well. The myofibril contain actin and myosin fibrils which do the contractions and make movement of H. diminuta possible. The contractile portions of the muscle cells are arranged in discrete bundles and propagation of contractions down the body make movement possible. The internal musculature of the scolex is complex, making the scolex extraordinarily mobile. The scolex has three distinct muscle types. The peripheral myofibers similar to those previously described, tentacle retractor muscles, and tentacle bulb muscles. The bulb muscles are obliquely striated and have numerous motor end plates. Thus the muscular system of H. diminuta is complex. (Andreassen, et al., 1999; Arai, 1980; Pappas, SEP 2000; Roberts and Janovy, 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)
Hymenolepis diminuta has no digestive tract, all nutrients needed must be absorbed by the tegument, which is the external covering of the cestode. The cestode is covered in tiny posteriorly directed microtriches which increase the absorbtive area of the tegument. The glycocalyx found on the surface membrane of the microtiches is a layer of carbohydrate-containing macromolecules. Interaction between the glycocalyx and certain molecules has been reported to enhance amylase activity in H. diminuta, inhibit the host trypsin, chymotrypsin, and pancreatic lipase and increase the absorption of cations and adsorbtion of bile salts. (Arai, 1980; Roberts and Janovy, 2000)
There is an extremely low chance for each egg to reach reproductive maturity and that is why H. diminuta lays so many eggs.
The adult worm lives in the intestine of its host, normally rats but also sometimes dogs and humans. Hymenolepis diminuta passes through the required intermediate arthropod host as a juvenile. Only when the intermediate host is injested by the definitive host will H. diminuta mature. The intermediate arthropod host is normally a grain beetle, and injestion of the intermediate host into the definative host normally occurs in piles of grain, where both rats and beetles live.
Hymenolepis diminuta is a cestode which sometimes causes infection in humans. Human infection results from eating such foods as dried fruits and precooked breakfast cereals in which the infected grain insects, themselves infected from eating rat or mouse droppings, are present. Some symptoms of infestation in humans include, enteritis, anorexia, headaches, anal pruritus, abdominal distress and small gut irritation. Hymenolepiasis is the term for a human to be infected with either H. diminuta or Hymenolepis nana, a dwarf sister species very closely related to H. diminuta. (Andreassen, et al., 1999; Arai, 1980; Roberts and Janovy, 2000)
Female rats parasitized with Hymenolepsis diminuta were quicker to retreive their young than non-infected rats. The rat's fitness, or contribution to the future gene pool is increased by investing more time in its present offspring since it's future survival is not known. (Willis and Poulin, 1999)
Renee Sherman Mulcrone (editor).
Stephen Dewey (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
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.
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).
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.
Andreassen, J., E. Bennet-Jenkins, C. Bryant. 1999. Immunology and biochemistry of Hymenolepis diminuta. ADV PARASIT, 42: 223-275.
Arai, H. 1980. Biology of the Tapeworm Hymenolepis diminuta. New York: New York Academic Press.
Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..
Centers for Disease Control and Prevention, 2002. "Hymenolepiasis" (On-line). Parasites and Health. Accessed 10/14/04 at http://www.dpd.cdc.gov/dpdx/HTML/Hymenolepiasis.htm.
Deines, K., . Richardson, G. Conlogue. JUL 1999. Radiographic imaging of the rat tapeworm, Hymenolepis diminuta. JOURNAL OF HELMINTHOL SOC W, 66 (2): 202-205.
Ohio State University, 2001. "Hymenolepis diminuta" (On-line). Parasites and Parasitological Resources. Accessed 10/14/04 at http://www.biosci.ohio-state.edu/~parasite/hymenolepis_diminuta.html.
Pappas, P. SEP 2000. Allometric growth of the proglottids and strobila of the tapeworm, Hymenolepis diminuta. J HELMINTHOL, 74 (3): 259-265.
Pappas, P., . Barley. APR 1999. Beetle-to-beetle transmittion and dispersal of Hymenolepis diminuta (Cestoda) eggs via the feces of Tenebrio molitor. JOURNAL OF PARASITOLOGY, 85 (2): 384-385.
Pappas, P., K. Ruthoford, A. Barley. 1999. Thermal tolerance of Hymenolepis diminuta eggs does not limit the parasite's distribution. Journal of Helminthology, 73 (1): 85-86.
Roberts, , Janovy. 2000. Foundations of Parasitology 6th ed.. McGraw-Hill Higher Education.
Shostak, A., K. Smyth. AUG 1998. Activity of flour beetles (Tribolium confusam) in the presence of feces from rats infected with rat tapeworm (Hymenolepis diminuta). CANADIAN JOURNAL OF ZOOLOGY, 76 (8): 1472-1479.
Sturdevant, L. 1907. Some Variations in Hymenolepis diminuta.
University of Aberdeen, 1997. "The life cycle, developmental sequence and crowding effect of the tapeworm *Hymenolepis diminuta*" (On-line). Biological and Soil Science. Accessed 10/14/04 at http://vcs.abdn.ac.uk/BIO_SOIL/parasite/contents.html.
Willis, C., R. Poulin. 1999. Effects of the tapeworm Hymenolepis diminuta on maternal investment in rats. Canadian Journal of Zoology, 77 (6): 1001-1005.