Current Advice on Parasite Control:
Intestinal Parasites - Cyclophyllidean Tapeworms
*Canine and feline cyclophyllidean cestodes are sometimes referred to as “true” tapeworms.
Overview of Life Cycle
- Cyclophyllidean cestodes have indirect life cycles that require specific intermediate hosts. Dogs and cats infected with adult cyclophyllidean tapeworms shed egg-laden proglottids in their feces. When the eggs are consumed by the appropriate intermediate host, larval cysts develop. Dogs and cats are infected when they ingest these larval cysts.
- The infectious egg has hooks that are characteristic of a cyclophyllidean cestode embyro.
Examples of larval cysts of cyclophyllidean cestodes include:
- cysticercoid, a compact form that uses an arthropod intermediate host
- cysticercus, a bladder-like cyst found in some tapeworm species that use a vertebrate intermediate host
- strobilocercus, a more developed form of a cysticercus found in the intermediate host of some tapeworm species
- coenurus, a large, bladder-like cyst found in some tapeworm species (e.g., T. multiceps)
- large, thick-walled unilocular hydatid cyst of E. granulosus
- large, thin-walled alveolar hydatid cyst of E. multilocularis
- Adult cyclophyllidean cestodes are found in the small intestine of an infected dog or cat.
- Proglottids are shed in the feces of an infected dog or cat.
- Disease in dogs and cats due to infection with adult cyclophyllidean cestodes is rare.
- Passage of proglottids may be associated with perianal irritation.
- Rare occurrences of tapeworms leading to impactions or linear-like foreign bodies have been reported.
- The reported prevalence of tapeworms in published studies varies from 4.0% to 60.0% in dogs and 1.8% to 52.7% in cats. A number of factors influence the likelihood that a dog or cat will be infected with tapeworms, including the geographic region and the opportunity the animal may have to ingest an infected intermediate host.
- Prevalence data generated by fecal flotation alone almost certainly underestimate the frequency of infection with cyclophyllidean cestodes because proglottids (and thus eggs) are focally distributed in fecal material and because eggs are heavy and thus do not readily float; a given fecal sample may be negative for tapeworm proglottids or eggs, even in the presence of an infection.
- Dipylidium caninum and Taenia spp. are found throughout North America. Currently, Echinococcus spp. are thought to be largely limited to areas of the northcentral, midwestern, and southwestern United States as well as areas of Canada and Alaska.
Host Associations and Transmission Between Hosts
- Both dogs and cats are susceptible to infection with D. caninum following ingestion of infected fleas or, more rarely, lice (Trichodectes canis).
- Echinococcus multilocularis will infect both dogs and cats following ingestion of rodents with alveolar hydatid cysts.
- Adults of Echinococcus granulosus and T. pisiformis are known to infect only dogs and wild canids. Infection of dogs occurs following ingestion of cysts in ungulate viscera or rabbit tissue, respectively.
- Adults of Taenia taeniaeformis infect only cats and wild felids and are acquired by ingestion of infected rodents.
Prepatent Period and Environmental Factors
- Dogs and cats may begin shedding proglottids of D. caninum, the common flea tapeworm, as soon as 2 to 3 weeks following infection. For Taenia spp. and Echinococcus spp., the prepatent period may be as long as 1 to 2 months.
Site of Infection and Pathogenesis
- Tapeworms are found in the small intestine 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. The common cyclophyllidean cestodes typically do not cause significant disease in dogs and cats, but because they are aesthetically unpleasant and may pose a zoonotic health risk, treatment is warranted.
- There have been reports of young puppies having intestinal impaction from massive D. caninum infections.
- A string-like foreign body reaction requiring surgery in a T. taeniaeformis infected cat has been reported.
- Diagnosis of infection with “true” tapeworms is reached by identifying proglottids in the fecal material or by recognizing eggs on fecal flotation.
- However, because proglottids are not uniformly distributed in the fecal material and eggs do not consistently float, fecal flotation alone is not a reliable means of diagnosing tapeworm infection in dogs and cats.
- Praziquantel, epsiprantel, and fenbendazole are approved for the treatment of certain tapeworm infections in dogs and cats.
- Praziquantel and epsiprantel are considered the treatments of choice because they are highly effective against D. caninum, the most common tapeworm of dogs and cats, as well as Taenia spp.
Praziquantel is approved at 5mg/kg orally or subcunateously for elimination of verious Taenia spp., Echinococcus spp., and D. caninum (dogs and cats).
- Only praziquantel is labeled as effective against Echinococcus spp. (not labeled as effective in all formulations; check “Product Applications for Dogs” for specific label claims).
- Epsiprantel can be administered at 5.5 mg/kg orally (dogs) and 2.75 mg/kg orally (cats) to eliminate infections with T. pisiformis and T. taeniaeformis, respectively, and for D. caninum.
- Fenbendazole at 50 mg/kg orally for three consecutive days will eliminate T. pisiformis (dogs).
- For dogs, praziquantel is formulated with some heartworm preventives to provide broad-spectrum internal parasite control. For cats, praziquantel is formulated with emodepside to provide broad-spectrum internal parasite control (check “Product Applications for Cats” for specific label claims).
- Treatment of tapeworms in dogs and cats must be combined with appropriate management, such as flea control and prevention of ingestion of prey species; in the absence of these changes, re-infection is likely to occur.
Control and Prevention
- In dogs that are allowed outside or that are known to have predatory behavior, a heartworm preventive containing praziquantel will routinely treat Taenia infections. Similarly, monthly treatments will treat infections with D. caninum obtained from the ingestion of fleas.
- Stringent adherence to controlling fleas and lice is required to prevent D. caninum in dogs and cats.
- Prevention of predation and scavenging activity by keeping cats indoors and dogs confined to a leash or in a fenced yard will limit the opportunity for dogs and cats to acquire infection with Taenia spp. or Echinococcus spp. via ingestion of cysts in intermediate hosts.
Public Health Considerations
- To prevent zoonotic infections,in areas where Echinococcus granulosus is endemic, routine monthly deworming of dogs with praziquantel should be strongly considered. In areas where E. multilocularis is known to be present, treatment of dogs and cats every three weeks with praziquantel is recommended.
- Echinococcus spp. infections are rare in humans in North America, and isolated reports of zoonotic infection with larval Taenia spp. of dogs and cats also exist. Although the overall risk of human infection with these parasites in North America appears extremely low, dogs and cats infected with these tapeworms do create a potential zoonotic risk. The eggs shed in the feces of an infected dog or cat are immediately infectious to the intermediate host. People who consume these eggs may develop cestode cysts requiring drainage, surgical removal, and/or extended treatment. In the case of E. multilocularis, surgery is unlikely to be successful, and long-term anthelminthic therapy may be required.
- Infections of children with D. caninum following ingestion of an infected flea are occasionally reported. The disease induced in the child is generally mild, confined to the intestinal tract, and readily treated, but can still be distressing to the family. If this is a concern to owners, the monthly administration of a heartworm preventive containing praziquantel in conjunction with an appropriate flea-control regimen will reduce the risk of the pet dog harboring these tapeworm infections.
- Conboy G. Cestodes of dogs and cats in North America. Vet Clin North Am Small Anim Pract 39:1075-1090, 2012.
- McManus DP, et al. Diagnosis, Treatment, and Management of Echinococcosis. BMJ Jun 11; 344:e3866, 2012.
- Raether W, Hänel H. Epidemiology, clinical manifestations and diagnosis of zoonotic cestode infections: an update. Parasitol Res 91:412-438, 2003.