Overview

Brief Summary

The Double-pored Dog Tapeworm (Dipylidium caninum) mainly infects dogs and cats, but is occasionally found in humans. The distribution of this tapeworm is worldwide and human infections have been reported from Europe, the Philippines, China, Japan, Argentina, and the United States.

Gravid proglottids (bisexual reproductive segments) are passed intact in the feces from the definitive host (i.e., the host in which adult parasites occur) or emerge from the perianal region of the host. Subsequently, these proglottids release typical egg packets. On rare occasions, proglottids rupture and egg packets are seen in stool samples. Following ingestion of an egg by an intermediate host (larval stages of the Dog or Cat Flea, Ctenocephalides spp.), an oncosphere is released into the intermediate host's intestine. The oncosphere penetrates the intestinal wall, invades the insect's hemocoel (body cavity), and develops into a cysticercoid larva. The larva develops into an adult and the adult flea harbors the infective cysticercoid. The vertebrate host becomes infected by ingesting an adult flea containing a cysticercoid. The domestic dog is the principal definitive host of D. caninum. Other potential hosts include cats, foxes, and humans (mainly children). Humans acquire infection by ingesting a cysticercoid-contaminated flea. This can result from close contact between children and their infected pets. In the small intestine of the vertebrate host, the cysticercoid develops into an adult tapeworm, reaching maturity around 1 month post-infection. The adult tapeworms (which reach up to around 60 cm in length and 3 mm in width) reside in the small intestine of the host, where each attaches by its scolex (the anterior part of the tapeworm that is specialized for attachment to the gut wall of the host). Each worm produces proglottids with two genital pores. The proglottids mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool, bringing the life cycle full circle.

(Centers for Disease Control Parasites and Health Website)

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Distribution

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.

Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian ; neotropical ; australian ; oceanic islands

Other Geographic Terms: cosmopolitan

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

Morphology

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.

Range length: 40 to 50 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

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

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.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest

Other Habitat Features: urban ; suburban ; agricultural

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

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.

Animal Foods: body fluids

Primary Diet: carnivore (Eats body fluids)

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

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.

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Ecosystem Impact: parasite

Species Used as Host:

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Animal / parasite / endoparasite
usually solitary tapeworm of Dipylidium caninum endoparasitises ilium of Felis domesticus

Animal / parasite / endoparasite
usually solitary tapeworm of Dipylidium caninum endoparasitises ilium of Canis familiaris
Other: major host/prey

Animal / parasite / endoparasite
larva of Dipylidium caninum endoparasitises larva of Ctenocephalides canis

Animal / parasite / endoparasite
larva of Dipylidium caninum endoparasitises Trichodectes canis

Animal / parasite / endoparasite
usually solitary tapeworm of Dipylidium caninum endoparasitises ilium of children of Homo sapiens
Other: unusual host/prey

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Life History and Behavior

Behavior

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.

Communication Channels: tactile

Perception Channels: tactile

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

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.

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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.

Key Reproductive Features: simultaneous hermaphrodite

Parental Investment: no parental involvement

  • Roberts, L., J. Janovy. 1996. Foundations of Parasitology 6th edition. USA: McGraw-Hill.
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Relevance to Humans and Ecosystems

Benefits

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)

Negative Impacts: injures humans (causes disease in humans ); causes or carries domestic animal disease

  • Currier, R., G. Kinzer, E. DeShields. 1973. Dipylidium caninum infection in a 14-month-old child. Southern Medical Journal, 66(9): 1060-2.
  • Reid, C., F. Perry, N. Evans. 1992. Dipylidium caninum in an infant. European Journal of Pediatrics, 151(7): 502-3.
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Wikipedia

Dipylidium caninum

Dipylidium life cycle

Dipylidium caninum, also called the flea tapeworm, double-pore tapeworm, or cucumber tapeworm (in reference to the shape of its cucumber-seed-like proglottids), though these also resemble grains of rice or sesame seeds), is a cyclophyllid cestode that infects organisms afflicted with fleas and canine chewing lice, including dogs, cats, and sometimes human pet-owners, especially children. The adult worm is about 18 inches (46 cm) long. Gravid proglottids containing the worm's microscopic eggs are either passed in the definitive host's feces or may leave their host spontaneously and are then ingested by microscopic flea larvae (the intermediate hosts) in the surrounding environment. These larvae eventually pupate and transform into adult fleas still carrying the tape worm, which are then ingested by a dog or cat during grooming activity. From there, the worm enters the animal's digestive tract and anchors itself to the intestinal wall where it will soon begin generating proglottids, completing the life cycle. Examples of fleas that can spread D. caninum include Ctenocephalides canis and Ctenocephalides felis.

As in all members of family Dipylidiidae, proglottids of the adult worm have genital pores on both sides (hence the name double-pore tapeworm). Each side has a set of male and female reproductive organs. The uterus is paired with 16 to 20 radial branches each. The scolex has a retractable rostellum with four rows of hooks, along with the four suckers that all cyclophyllid cestodes have.

In children, infection causes diarrhea and restlessness. As with most tapeworm infections, the drugs of choice are niclosamide or praziquantel. The best way to prevent human infection is to treat infected animals to kill fleas. Tapeworm infection usually does not cause pathology in the dog or cat, and most pets show no adverse reaction to infection other than increased appetite.

The other tapeworm infecting cats is Taenia taeniaeformis, though this form is much less commonly encountered that the one currently under discussion here.

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