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Dipylidium caninum

By Elizabeth Hodgson and Eric Knapp

Geographic Range

Dipylidium caninum is a world-wide parasite of dogs and cats that requires a flea intermediate host to develop. Therefore its range is dependent upon the availability of both flea and vertebrate hosts, as well as the ability to survive outside of the host until ingested by a flea. (Roberts and Janovy, 1996)

Habitat

The first habitat for these organisms is feces of the definitive hosts, where they are still eggs. Next they live in fleas, which accquire the parasites by eating the feces. If the flea is eaten by a dog, the larval worm finds itself in the intestine where it becomes an adult and remains the rest of its life. Humans can also host the worms. We accquire them by accidentally ingesting fleas from a pet that has fleas containing juvenile worms. (Reddy, 1982)

Physical Description

A Dipylidium caninum adult is a long flat worm, around 40 to 50 cm. The body is made up of the head or scolex, the neck, and a segmented section called the strobilus. The scolex has hooks for attachment. Each segment contains two proglottids. A proglottid is one set of reproductive organs. Dipylidium caninum is often identified by examing segments passed in feces. Dipylidium caninum has two genital pores located laterally on each segment, with two proglottids per segment. Segments are often described as resembling cucumber seeds, and are quite active when seen outside their hosts in fecal material. Larvae are called oncospheres generally, but specifically for D. caninum. Larvae of Eucestoda are termed "hexacanth" because of the six hooks on the posterior end. (Chappell, et al., 1990; Roberts and Janovy, 1996)

  • Range length
    40 to 50 cm
    15.75 to 19.69 in

Development

Dipylidium caninum is monoecious, or hermaphroditic. Each segment of its strobilus has two sets of male and female reproductive organs (proglottids). Each proglottid will eventually contain about a dozen eggs. Segments break free from the body of the worm and exit the host via fecal excretion, where they are then available for ingestion by the intermediate host, fleas. Fleas feeding on dog feces ingest the segment. Inside the flea the egg develops into the larval form called the cysticercoid, which is not sexually mature. When it finally reaches its definitive host it can reach sexual maturity. (Roberts and Janovy, 1996)

Reproduction

When Dipylidium caninum finally reaches its definitive host it can reach sexual maturity. Only one individual is necessary for reproduction since these worms are monecious, or hermaphroditic. Each segment of its strobilus has two sets of male and female reproductive organs (proglottids). Each proglottid will eventually contain about a dozen eggs. Segments break free from the body of the worm and exit via feces. Because of the complexity of this process it is necessary for these worms to have high reproductive potentials. In fact, tapeworms are known to produce anywhere from a few to millions of eggs in their lifetimes. (Roberts and Janovy, 1996)

  • Key Reproductive Features
  • simultaneous hermaphrodite
  • Parental Investment
  • no parental involvement

Behavior

Dipylidium caninum, known as the dog tapeworm, is a parasite of dogs, and sometimes cats and humans. Human infections occur most commonly in children. Its life cycle requires the use of two hosts, a flea and a vertebrate. The tapeworm eggs are ingested by flea larvae, where development reaches the larval cysticercoid stage. The vertebrate host is reached when an infected flea is ingested by the vertebrate. The worm reaches adulthood in the vertebrate and proglottids containing eggs (gravid proglottids) are excreted with feces to renew the cycle. The hexacanth larva uses its hooks to transport itself from the gut of the flea into the hemocoel. In the hemocoel, larval development continues into further juvenile stages. When detached segments are excreted from the vertebrate host, they are mobile and can easily be seen crawling around. (Chappell, et al., 1990; Roberts and Janovy, 1996)

Communication and Perception

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)

Food Habits

Dipylidium caninum attaches itself to the intestinal lumen of its definitive host (dogs, cats, or sometimes humans) as an adult. Its hooked scolex is specialized to hold it in place in the intestine. Dipylidium caninum, and all cestodes lack digestive tracts. It feeds by absorption through its body covering, or tegument. Because of this absorption method of feeding it is logical that the worms have evolved to locate themselves in the intestines of their hosts, where the partially digested food is of maximum benefit. (Neafie and Marty, 1993; Roberts and Janovy, 1996)

  • Animal Foods
  • body fluids

Predation

The tapeworms are probably not intentially eaten. However, mortality is high at the egg and larval stages because the tapeworms do not reach a suitable host.

Ecosystem Roles

Species Used as Host

Economic Importance for Humans: Negative

Infection with D. caninum is often asymptomatic in humans, though there are some reports of abdominal pain, diarrhea, irritability, and anal pruritis (Reddy, 1982). There is no discussion of pathogenicity in the dog or cat hosts, however Chappell states that infections in humans are usually limited to one worm. If the same is true for dogs and cats, then the effects of infestation should be similar. Other reports show contrary evidence, that up to 25% of infections involve multiple worms in human cases, though no difference in pathogenicity was mentioned. (Currier 1973)

Almost all infections in humans are found in children, even infants (Reid et. al, 1992). The most likely cause of this pattern of infection is the proximity and duration of play between children and canine or feline pets. Behavior that is particulary advantageous from the tapeworm's point of view is mouth to mouth contacts between human and animal, because a recently nipped flea can still be on the mouth of the pet and then be passed into the human. A doctor from Delaware advised that "the habit of kissing canines should not be encouraged". (Reddy 1982) (Currier, et al., 1973; Reddy, 1982; Reid, et al., 1992)

Contributors

Renee Sherman Mulcrone (editor).

Elizabeth Hodgson (author), University of Michigan-Ann Arbor, Eric Knapp (author), University of Michigan-Ann Arbor, Solomon David (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

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.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

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.

cosmopolitan

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.

desert or dunes

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.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

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.

motile

having the capacity to move from one place to another.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

rainforest

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 forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

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).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

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.

savanna

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.

temperate grassland

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.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

References

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Chappell, C., J. Enos, H. Penn. 1990. Dipylidium caninum, an underrecognized infection in infants and children. Pediatric Infectious Disease Journal, 9(10): 745-7.

Currier, R., G. Kinzer, E. DeShields. 1973. Dipylidium caninum infection in a 14-month-old child. Southern Medical Journal, 66(9): 1060-2.

Neafie, R., A. Marty. 1993. Unusual Infections in Humans. Clinical Microbiology Reviews, 6(1): 34-56.

Ohio State University, 2001. "Dipylidium caninum (Cucumber tapeworm)" (On-line). Parasites and Parasitological Resources. Accessed October 04, 2004 at http://www.biosci.ohio-state.edu/~parasite/dipylidium.html.

Reddy, S. 1982. Infestation of a Five-Month-Old Infant with Dipylidium Caninum. Delaware Medical Journal, 54(8): 455-6.

Reid, C., F. Perry, N. Evans. 1992. Dipylidium caninum in an infant. European Journal of Pediatrics, 151(7): 502-3.

Roberts, L., J. Janovy. 1996. Foundations of Parasitology 6th edition. USA: McGraw-Hill.

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