Chapter 337. Dipylidiasis

Dogs and cats are often infected with the dog tapeworm, Dipylidium caninum. Gravid proglottids may actively migrate from the animal’s anus or from fecal material and disintegrate, spreading tapeworm eggs in the environment. Larvae of dog and cat fleas (more rarely the dog louse and the human flea) ingest the eggs and act as intermediate hosts, with the tapeworm larvae maturing in the flea. When a dog or cat ingests an infected adult flea, the larvae are released, and the adult tapeworm develops in the animal’s small intestine about 1 month after infection. A single flea may contain multiple tapeworm larvae, and infection with more than 1 tapeworm is possible.1,2

Humans can acquire the infection by accidental ingestion of an infected flea. Dipylidiasis in humans is much more common in young children and infants than in adolescents and adults; infection in a 5-week-old infant has been described. As in animals, the larvae in the child grow to maturity in the small intestine, and gravid segments of the adult tapeworm continually detach singly or in chains and migrate out of the anus, independently of stool.2,3

Clinical Manifestations, Diagnosis, and Treatment

The infection is often asymptomatic, but some patients may show loss of appetite, indigestion, abdominal pain, diarrhea, anal pruritus, poor weight gain, and irritability. Clinically, an initial diagnostic suspicion may arise from the description of the worm given by the parent or caretaker. Eosinophilia and urticaria have also been described, but are not consistent findings.4

The diagnosis is made by the identification of excreted proglottids or the finding of characteristic egg packets in stool. Routine fecal examinations may be falsely negative, because the eggs disintegrate rapidly, are not routinely released in the intestine, and proglottids migrate out of fresh fecal specimens. The first sign of infection is often the appearance of the proglottids on the stool or in the infant’s diaper. A common error is to assume that these motile objects are pinworms or fly larvae. The parent should be asked to collect the proglottids in saline (alcohol or other fixatives make the proglottids opaque and brittle) and bring them to the laboratory. Compression of the proglottid between glass microscope slides will reveal the bilateral genital pores.1,3

While human infection is self-limited unless there is repeated exposure from the environment, praziquantel is effective when given in a single dose of 5 to 10 mg/kg. Patients should be informed that the drug is considered investigational by the FDA if used for this purpose. Niclosamide is also effective but is no longer available in the United States.3,4