Canis ISSN: 2398-2942

Taenia ovis

Synonym(s): T. ovis

Contributor(s): Dwight Bowman

Introduction

Classification

Taxonomy

  • Class: Cestoda.
  • Family: Taeniidae.
  • Genus: Taenia.

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Clinical Effects

Epidemiology

Habitat

  • Adult tapeworm in small intestine of rural dogs that are fed or scavenge raw sheep meat, and in other Canidae.
  • Segments and eggs in environment.
  • Metacestode (cysticercus) in muscles of sheep.

Lifecycle

  • See lifecycle diagram Lifecycle Taenia ovis - diagram :
    • Adult tapeworm.
    • Gravid proglottid.
    • Egg.
    • Metacestode (cysticercus).

Transmission

Transmission to sheep
  • Segments migrate out of anus and fall to the ground Taenia spp segment migrating spontaneously from the anus.
  • Segments passed in feces migrate out onto grass or soil.
  • As segments migrate they leave a trail of thousands of eggs in a gelatinous film over the surface of grass, etc Taenia spp egg film from migrating segment.
  • Eggs left by segments on feces can be eaten by flies and deposited over pasture.
  • Eggs eaten with herbage by sheep.
Transmission to dog
  • Metacestode (cysticercus) in muscles of sheep eaten when dog is scavenging or fed sheep meat.

Pathological effects

  • Very little protective immunity develops in the dog population.
  • Protection in sheep is rapidly induced by prior infection. Protection is largely antibody- and complement-mediated and persists for about 3-9 months in the absence of reinfection.
  • Cysts die in up to 6-9 months and are invaded by inflammatory cells with eosinophilic caseation and calcification.

In dog

  • The presence of tapeworms (1 or many) usually has little effect on the health of a well-fed dog.
  • Irritation of a segment spontaneously migrating from the anus can cause 'scooting'.
  • Very large numbers of worms in young, poorly-nourished dogs could reduce growth rates Tapeworm in a dogs intestine.
  • Very rarely, obstruction of the intestine from many hundreds of worms can occur.

In sheep

  • Cysts have a predilection site for the heart, diaphragm and masseters, but occur all over the carcass. Dead cysts are caseous or calcified, cream or greenish, eosinophilic lesions up to 0.5-1 cm long.

Control

Control via animal

  • Anthelmintic treatment of dog.
  • Dogs should be well-fed and prevented from scavenging, and should not be fed sheep meat.
  • Uncooked sheep meat should not be fed to dogs.

Control via chemotherapies

  • Drugs with efficacy against Taenia pisiformis or Taenia hydatigena should be used.
  • Praziquantel Praziquantel.
  • Epsiprantel.
  • Nitroscanate Nitroscanate (not available in US).
  • Fenbendazole Fenbendazole.
  • Mebendazole Mebendazole (not available in US).
  • Dichlorophene not recommended.

Vaccination

  • Not available outside of Australia and New Zealand.
  • A host-protective antigen encoded by an incomplete DNA, known as 45W, has been identified. A T. ovis fusion protein GST-45W(B/X) has been expressed in exclusion bodies in genetically modified Escherichia coli. The vaccine has been grown in commercial quantities and registered in Australia and New Zealand. Other protective antigens To18 and To16.17 have been identified.

Other countermeasures

  • Where examined, Taenia hydatigena Taenia hydatigena and Taenia ovis Taenia ovis are in a highly stable, hyperendemic steady state. The reproduction rate for these is 4.0-5.0. This is because sheep readily acquire immunity to infection after eating as few as 10 eggs (with cross-immunity between the 2 tapeworms).
  • Taenia species have a high biotic potential producing millions of eggs, so sheep become infected with 1 or 2 cysts of either tapeworm very early in life, develop immunity and cross-immunity, and this immunity is continuously boosted through the life of the sheep. As a result very few Taenia ovis cysts occur in the sheep population.
  • Anthelmintic treatments instituted for Echinococcus granulosus are never sufficient to eradicate Taenia species because of their high biotic potential but, in New Zealand, the 6-weekly treatments were sufficient to reduce the numbers of worms in dogs, eventually reaching levels where sheep were no longer necessarily infected early enough in life to develop immunity and immunity was not continuously boosted.
  • The Taenia tapeworms had been pushed to an unstable endemic steady state so that numbers of cysts in the muscles of sheep rose with age through continual reinfection in the absence of the boosting of immunity.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Dempster R P, Robinson C M & Harrison G B L (1996) Parasite vaccine development - large scale recovery of immunogenic Taenia ovis fusion protein GST-45W(B/X) from Escherichia coli inclusion bodies. Parasitol Res 82, 291-296.
  • Lawson J R (1994) Hydatid disease and sheep measles - the history of their control and economics of a recent change in control policy. NZ J Zoology 21, 83-89.

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