Taenia spp.

Synopsis

CAPC Recommends

• Treating intestinal Taenia spp. infections in dogs with appropriate anthelmintics.
• Reducing opportunities for dogs to catch prey, which can result in reinfection.
• Using PCR tests offered at diagnostic labs to molecularly differentiate Taenia spp. eggs from Echinococcus spp. eggs when appropriate.

Species

Species

Canine
Taenia crassiceps
Taenia hydatigena
Taenia multiceps
Taenia pisiformis
Taenia serialis

Overview of Life Cycle

• Taenia spp. are cyclophyllidean cestodes with indirect life cycles that require specific intermediate hosts. Dogs infected with adult cyclophyllidean tapeworms shed egg-laden proglottids in their feces. When the appropriate vertebrate intermediate host consumes the eggs, larval cysts develop. Dogs are infected when they ingest these larval cysts while preying on or scavenging infected vertebrates.

Stages

• Taenia spp. eggs contain an embryo with six hooks (hexacanth embryo) and are morphologically indistinguishable from those of Echinococcus spp. - often referred to as Taeniid type eggs.
• Examples of metacestodes of Taenia spp. in the intermediate host include:
  • cysticercus, a small, bladder-like cyst
  • coenurus, a large, bladder-like cyst
  • strobilocercus, a more developed form of a cysticercus with an extended segmented body

Metacestodes and intermediate hosts of selected Taenia spp.

T. crassiceps

• Definitive Host: Dog
• Metacestode: Cysticercus
• Intermediate Host: Rodents
• Location in Intermediate Host: Viscera

T. hydatigena

• Definitive Host: Dog
• Metacestode: Cysticercus
• Intermediate Host: Wild ruminants, horses, and pigs
• Location in Intermediate Host: Viscera

T. multiceps

• Definitive Host: Dog
• Metacestode: Coenurus
• Intermediate Host: Sheep
• Location in Intermediate Host: Brain and spinal cord

T. pisiformis

• Definitive Host: Dog
• Metacestode: Cysticercus
• Intermediate Host: Rabbits
• Location in Intermediate Host: Viscera

T. serialis

• Definitive Host: Dog
• Metacestode: Coenurus
• Intermediate Host: Rabbits and Rodents
• Location in Intermediate Host: Subcutaneous and intramuscular connective tissue

• Adult Taenia species are found in the small intestine of an infected dog.
  • The scolex of the Taenia species common in dogs in North America has two rows of hooks for attachment to the small intestine mucosa.
• Proglottids are shed in the feces of an infected dog. When proglottids rupture, eggs may be shed.

Disease

• Disease in dogs and cats due to infection with adult Taenia species is rare.

• Passage of proglottids may be associated with perianal irritation.

• Occasional intestinal impactions with Taenia spp. necessitating surgical removal of a mass of tapeworms from the small intestine have been reported.

• Rare reports of aberrant infection with metacestodes of Taenia spp. leading to severe disease in dogs also exist.

Prevalence

• Taenia species are commonly found in dogs throughout North America.

• A number of factors influence the likelihood that a dog 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 because proglottids (and thus eggs) are focally distributed in fecal material; a given fecal sample may be negative for tapeworm proglottids or eggs, even in the presence of an infection.

Host Associations and Transmission Between Hosts

• Adults of Taenia pisiformis are known to infect only dogs and wild canids. Infection of dogs occurs following ingestion of cysticerci in rabbit tissue.
• Other Taenia species are considered less common in domestic dogs in North America although they are occasionally reported (see Stages)
• In the absence of predation or opportunities for scavenging, infection with Taenia spp. will not occur.

Prepatent Period and Environmental Factors

• Dogs begin shedding proglottids of T. pisiformis between 1.5-2 months following infection

• Eggs can remain viable for up to a year in ideal conditions, low temperature and high humidity, but are susceptible to desiccation under high temperature/ low humidity conditions. Under harsh conditions, eggs may only persist in the environment for 1 week.

Site of Infection and Pathogenesis

• Taenia spp. typically do not cause significant disease in dogs, but because they are aesthetically unpleasant to pet owners, treatment is warranted.

Diagnosis

• Diagnosis of infection is reached by identifying proglottids in the fecal material, eggs on centrifugal fecal flotation, or PCR.
• Fecal flotation with centrifugation
  • Diagnosis of patent Taenia infections via centrifugal fecal flotation can be challenging as eggs are quite dense. Click here to see Fecal Examination Procedures. Examine for characteristic taeniid eggs.
  • Centrifugation is also available using AI assisted reading.
  • The use of sugar solution and centrifugation can increase the sensitivity of Taenia egg detection.
  • Eggs of Taenia sp. cannot be differentiated morphologically from those of Echinococcus sp.
  • Due to the similarity to Echinococcus eggs and its zoonotic potential, extreme caution should be use when processing samples.
  • 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 infections in dogs and cats.
  • Proglottids of Taenia spp. have a characteristic rectangular shape with a single, lateral genital pore.
    • Proglottids of Echinococcus spp. are microscopic, and therefore releasing taeniid eggs from a macroscopic, rectangular proglottid is useful in differentiating the two parasites.
  • Taenia species eggs are 25-40 μm in diameter and are brown with a thick, striated shell wall. The developing embryo has 6 hooks.
• PCR is available at commercial diagnostic laboratories which can be used for differentiation of Taenia spp. eggs from Echinococcus spp. eggs.
  • Nucleic acid is stable in the feces for 10 days at 4ºC.

Treatment

• Praziquantel and epsiprantel are approved for the treatment of Taenia spp. infections in dogs. Febendazole is also approved for the treatment of Taenia pisiformis in dogs.

• For dogs, praziquantel is formulated with some heartworm preventives to provide broad-spectrum internal parasite control. 

• Treatment of Taenia spp. in dogs must be combined with management changes to prevent ingestion of vertebrate 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 infections with Taenia spp. and other cyclophyllidean cestodes. 

• Prevention of predation and scavenging activity by keeping dogs confined to a leash or in a fenced yard will limit the opportunity for dogs to acquire infection with Taenia spp.

Public Health Considerations

• Isolated reports of zoonotic infection with larval Taenia spp. of dogs exist. However, the overall risk of human infection with Taenia spp. in North America appears extremely low.

• Other Taenia species of significant public health concern include T. saginata and T. solium, but neither are parasites of domestic cats and dogs. Humans are the definitive host for both of these species, and they become infected via the ingestion of cysticerci in beef or pork, respectively.

Selected References

• Conboy G. Cestodes of dogs and cats in North America. Vet Clin North Am Small Anim Pract 39:1075-1090, 2009.

• Raether W, Hänel H. Epidemiology, clinical manifestations and diagnosis of zoonotic cestode infections: an update. Parasitol Res 91:412-438, 2003.