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Causal Agent:

Dipylidium caninum (the double-pored dog tapeworm) mainly infects dogs and cats, but isoccasionally found in humans.

Life Cycle:

Gravid proglottids are passed intact in the feces or emerge from the perianal region of the

host . Subsequently they release typical egg packets . On rare occasions, proglottids

rupture and egg packets are seen in stool samples. Following ingestion of an egg by the

intermediate host (larval stages of the dog or cat flea Ctenocephalides spp.), an oncosphere

is released into the flea's intestine. The oncosphere penetrates the intestinal wall, invadesthe insect's hemocoel (body cavity), and develops into a cysticercoid larva . The larva

develops into an adult, and the adult flea harbours the infective cysticercoid . The

vertebrate host becomes infected by ingesting the adult flea containing the cysticercoid .The dog is the principal definitive host for Dipylidium caninum. Other potential hosts

include cats, foxes, and humans (mostly children) , . Humans acquire infection by

ingesting the cysticercoid contaminated flea. This can be promulgated by close contactbetween children and their infected pets. In the small intestine of the vertebrate host the

cysticercoid develops into the adult tapeworm which reaches maturity about 1 month after

infection . The adult tapeworms (measuring up to 60 cm in length and 3 mm in width)reside in the small intestine of the host, where they each attach by their scolex. They

produce proglottids (or segments) which have two genital pores (hence the name "double-

pored" tapeworm). The proglottids mature, become gravid, detach from the tapeworm, andmigrate to the anus or are passed in the stool .

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Geographic Distribution:Worldwide. Human infections have been reported in Europe, the Philippines, China, Japan,Argentina, and the United States.

Clinical Features:Most infections with Dipylidium caninum are asymptomatic. Pets may exhibit behavior torelieve anal pruritis (such as scraping anal region across grass or carpeting). Mild

gastrointestinal disturbances may occur. The most striking feature in animals and childrenconsists of the passage of proglottids. These can be found in the perianal region, in the

feces, on diapers, and occasionally on floor covering and furniture. The proglottids aremotile when freshly passed and may be mistaken for maggots or fly larvae.

Laboratory Diagnosis:The diagnosis is made by demonstrating the typical proglottids or egg packets in the stoolor the environment.

Treatment:

Treatment for both animals and humans is simple and very effective. Praziquantel is giveneither orally or by injection (pets only). The medication causes the tapeworm to dissolvewithin the intestines. Since the worm is usually digested before it passes, it may not be

visible in the dog's stool. These drugs are generally well tolerated. For additional

information, see the recommendations in The Medical Letter (Drugs for ParasiticInfections).

Microscopy

Eggs

Dipylidium caninum eggs are round to oval (average size 35 to 40 µm; range 31 to 50 µmby 27 to 48 µm) and contain an oncosphere that has 6 hooklets. Proglottids of D. caninum

contain characteristic egg packets that are round to ovoid and contain 5 to 15 or more eggseach.

A B

A: D. caninum egg packet, containing 8 visible eggs, in a wet mount.

B: D. caninum eggs clumped together in a wet mount; image taken at 400× magnification.Note that hooklets in the some of the eggs are visible.

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Proglottids

Dipylidium caninum proglottids (average mature size 12 mm × 3 mm) have two genitalpores, one in the middle of each lateral margin. Proglottids may be passed singly or in

chains, and occasionally may be seen dangling from the anus. They are pumpkin seed-

shaped when passed and often resemble rice grains when dried.

C D

C: D. caninum proglottid under a dissecting microscope cleared with lactophenol.

D: D. caninum proglottid partially cleared with lactophenol, showing eggs and egg packets.

ScolexThe scolex of Dipylidium caninum is conical-shaped and has four suckers. There is also a

retractable rostellum armed with several rings of small spines, used for anchoring into the

host’s tissue.

E

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E: D. caninum scolex.

Macroscopic (Gross) Observations

F

F: Adult tapeworm of Dipylidium caninum; adults measure 10-70 cm long. The scolex of the worm is very narrow and the proglottids get larger as they mature.