This report documents praziquantel-resistant Dipylidium sp. that was effectively treated with nitrosconate and highlights the novel use of capsule endoscopy for assessing parasite burden. Throughout this case report, the efficacy of anthelmintic therapy was evaluated by repeated testing. Monitoring the stool, grossly and through fecal flotation and Giardia ELISA, ruled out other differential diagnoses and assessed if treatment effectively resolved the Dipylidium sp. infection. Additionally, capsule endoscopy provided direct visualization of adult tapeworm scolices, with segments attached to the small intestinal mucosa or remaining proglottids.
Limitations of this case report include the inability to assess the efficacy of environmental decontamination done at the patient's home. Flea infestations are difficult to eliminate in a household, especially when the infestation source, usually a pet, continually re-introduces fleas. Although an over-the-counter “flea bomb” was used, it is a possibility that insufficient environmental decontamination may confound the repeated appearance of tapeworm segments in the stool. Although helpful in visualizing the small intestine, images obtained from capsule endoscopy were occasionally obscured by intestinal content, making visualization difficult.
Dipylidium caninum is the most common tapeworm in dogs and cats, with a prevalence ranging from 4.0–60.0% [5], with some reports as low as 0.3% [7]. The recommended treatment of this tapeworm is 5 mg/kg of praziquantel [4]; however, the exact dosage often varies, as products sold contain fixed amounts of the drug and are labeled for specific weight ranges. This drug tends to have mild to no adverse effects (anorexia, vomiting, lethargy, diarrhea). It is commonly given at higher doses or repeated weekly, or even daily, to treat some infections. One study found that dogs treated with six times the recommended therapeutic dose only occasionally vomited [2]. Typically, Dipylidium caninum infections cause little to no clinical signs in dogs and cats. On the rare occasion that dipylidiasis causes clinical signs, abdominal pain, vomiting, diarrhea, and mild anal pruritus may be encountered.
Several challenges were encountered in this case. In tapeworm infections involving flea infestations, re-infection is common, as fleas continually hatch in the environment, and a patient may ingest these new fleas after treatment. Thus, praziquantel resistance may be mistakenly assigned to situations where the infection was only temporarily eliminated. Additionally, there is a pre-patent period of approximately 2.5 weeks after infection before dogs and cats begin to shed proglottids that can be seen in feces [5].