Tapeworms are frequently recognized parasites in both dogs and cats in the United States. Dipylidium caninum and Taenia species are the most commonly reported, but other genera, including Echinococcus, Mesocestoides, Spirometra, and Diphyllobothrium, may be regionally important. These cestodes are widely considered nonpathogenic; however, tapeworms may occasionally cause disease in both pets and people. Careful attention is needed both to prevent tapeworm infections and to ensure prompt, effective treatment when infections do occur.
Susan E. Little, DVM, PhD, DEVPC
All cestodes have indirect life cycles, which require specific intermediate hosts (Table 1). Of the two major groups of cestodes found in dogs and cats (cyclophyllidean and pseudophyllidean), the cyclophyllidean tapeworms, or true tapeworms, are more common. Dogs and cats infected with adult cyclophyllidean tapeworms, such as Dipylidium caninum or Taenia, Mesocestoides, or Echinococcus species, shed egg-laden proglottids in their feces. When the appropriate intermediate host consumes these eggs, larval cysts develop. Dogs and cats are infected when they ingest the intermediate host that contains these larval cysts. These pets may then begin shedding proglottids of D. caninum, the common flea tapeworm, or Mesocestoides species as soon as two or three weeks after infection. For Taenia and Echinococcus species, the prepatent period may be as long as one or two months.1
In contrast, adult pseudophyllidean cestodes, such as Spirometra species or Diphyllobothrium latum, discharge individual operculated eggs through a median genital pore. These eggs hatch upon contact with water and develop in a copepod first intermediate host and a vertebrate second intermediate host before being ingested by a cat or dog definitive host and developing into an adult tapeworm. Dogs and cats may begin shedding pseudophyllidean tapeworm eggs as soon as 10 days after infection. Infections will only occur when dogs and cats ingest larvae in prey species or in undercooked animal tissue in an area where infection is cycling in nature.1
Table 1: Intermediate Hosts of the Common Tapeworms in Dogs and Cats
Adult tapeworms reside in the small intestines of dogs and cats. Motile proglottids may be seen in the perianal region as they exit the animal, in the pet's environment (e.g. on bedding), or in the fecal material itself.
Although the common cestodes of dogs and cats, such as Dipylidium caninum and Taenia species, usually do not cause significant disease in pets,1 tapeworm infections are aesthetically unpleasant. The presence of proglottids on pets or in the home may cause distress to clients and can fracture the human-animal bond. In addition, infection of pets with these parasites poses a zoonotic health risk in the home. In contrast, the less commonly seen Mesocestoides species may occasionally induce peritoneal cestodiasis, and both Spirometra and Diphyllobothrium species have been associated with gastrointestinal disease characterized by vomiting, diarrhea, and weight loss in infected cats and dogs.2 For all of these reasons, control and treatment of tapeworms in pets is warranted.