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INTRODUCTION

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Dipylidiasis is caused by Dipylidium caninum, which is a relatively common tapeworm of dogs and cats worldwide. The infection of humans is a rare occurrence and most often affects infants and children.

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PATHOGENESIS AND EPIDEMIOLOGY

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Gravid motile proglottids from D caninum may actively migrate through the host’s anus or be passed with fecal material disintegrating in the environment and dispersing egg-containing sacs (Fig. 332-1). Dog, cat, and human flea larvae and larvae of the dog louse ingest the eggs (35–40 μm) and serve as the intermediate host. In the larvae intestine, oncospheres are released and develop into cysticercoids within the intestinal wall. When a dog, cat, or rarely human ingests an infected adult flea, the cysticercoid larvae are released, and the adult tapeworm measuring between 10 and 70 cm develops in the small intestine of the definitive host in about 3 to 4 weeks after infection. A single flea may contain multiple Dipylidium larvae, and infection with more than 1 tapeworm is possible in the definitive host.

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Figure 332-1

Dipylidium caninum proglottid. The inset shows an egg sac containing eggs with hooks (arrows). (Used with permission from Dr. Miguel M. Cabada, University of Texas Medical Branch and Tropical Medicine Institute–Cusco Branch, Universidad Peruana Cayetano Heredia, Cusco, Peru.)

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This is the most common and widespread adult tapeworm of dogs and cats and can be found worldwide, although not commonly in the United States. Humans acquire the infection by accidental ingestion of infected flea. Dipylidiasis in humans is almost exclusively reported in young children and infants as they are prone to accidentally ingest fleas or have contact with saliva of pets that may contain cysticercoids. In children, gravid proglottids passed in the stool may be confused with other parasites like Enterobius or fly larvae, delaying the diagnosis.

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CLINICAL MANIFESTATIONS

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The infection by D caninum is often asymptomatic, but some patients may show decreased appetite, dyspepsia, abdominal pain, diarrhea, anal pruritus, poor weight gain, and irritability. Clinically, the parents’ description of small worms or “maggots” found on diapers or underwear should raise suspicion for dipylidiasis. Eosinophilia and urticaria have been described but are not consistent findings.

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DIAGNOSIS

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Microscopic inspection of the sacs of eggs or excreted proglottids passed by the host gives the diagnosis. Isolated eggs are not commonly found in stools because the gravid proglottids do not release eggs within the intestine. Fecal examinations may be falsely negative, because proglottids migrate to the surface of the stool sample and may be mistaken as fly larvae, “maggots,” or vegetable matter. The first sign of infection is often the appearance of the proglottids in the stool or in the infant’s diaper. The parent should be asked to collect the proglottids in saline ...

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