Canis ISSN: 2398-2942

Echinococcosis

Contributor(s): Maggie Fisher, Alex Morrow, Bryn Tennant

Introduction

  • A serious zoonotic infection with adult tapeworms or the larval hydatid cysts of the genus Echinococcus.
  • Cause: dogs are the principal or occasional definitive host of a number of species of Echinococcus.
  • Three main species, E. granulosusE. multilocularis and E. vogeli, infect dogs in different parts of the world.
  • For some time it has been recognized that different strains of E. granulosusexist and several of these have recently been reclassified as distinct species (see geographic distribution).
  • Signs: humans become infected with the metacestode stage resulting in the formation of hydatid cysts in various organs.
  • Dogs infected with the adult tapeworm show few, if any, clinical signs.
  • Diagnosis: in the definitive host fecal examination using PCR, Coproantigen or microscopy.
  • In humans a variety of diagnostic tests are used including serology.
  • Treatment: praziquantel eliminates infection with adult worms in the dog.

Pathogenesis

Etiology

  • Two main species, Echinococcus granulosus Echinococcus granulosus and E. multilocularis Echinococcus multilocularis , with a third species E. vogeli having a more restricted distribution.
  • The domestic dog is the principal definitive host of E. granulosus and an occasional definitive host of the other two species mentioned.
  • Intermediate hosts of:
    • E. granulosus are ungulates (and humans).
    • E. multilocularis are rodents (and humans).
    • E. vogeli are paca and other rodents.
  • Wild carnivores can be a source of infection for domestic animals and humans.

Specific

  • Feeding uncooked meat or offal containing viable cysts.
  • Dogs scavenging or predation.

Pathophysiology

Definitive host

  • Dogs acquire infection by ingesting the metacestode stage or hydatid (E.granulosus) or alveolar (E. multilocularis) cysts, containing infective proscolices, in an intermediate host.
  • The pathogenic effect of adult tapeworms in the definitive host, including the domestic dog, is low irrespective of challenge.
  • Enteritis may occur occasionally in heavily infested dogs.

Intermediate hosts

  • Intermediate hosts, including man, are infected by ingestion of eggs passed in dog feces.
  • In intermediate hosts Echinococcus hatch in the lumen of the intestine, penetrate the intestinal wall → hepatic portal system → liver → form cysts. The liver is the primary predilection site.
  • With E. multilocularis undifferentiated germinal cells occasionally break free from the cyst and metastasize to other organs, especially the lungs and brain.
  • The cysts of E.multilocularis are not restricted by a fibrous capsule and thus progressively expand into surrounding host tissue through the growth of tubular processes.
  • Cysts develop slowly in the intermediate host (becoming infective in 2-4 years in the case of E granulosus and 40-60 days for E. multilocularis) but in rodents the cyst can eventually kill them.

Timecourse

  • Under suitable conditions the proscolices can survive for 1-2 weeks after the death of the intermediate host.
  • Onset of egg production ranges from 28-35 days after infection with E. multilocularis and about 7 weeks after infection with E. granulosus.

Epidemiology

  • Eggs excreted by infected dogs are fully embryonated and are immediately infective for intermediate hosts.
  • E. multilocularis and E. granulosus eggs can remain infective in the environment for at least 6 months.
  • Insects, such as blowflies, and birds may be important in dispersing eggs from feces.

Diagnosis

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Treatment

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Prevention

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Corsini M et al (2015) Clinical presentation, diagnosis, therapy and outcome of alveolar echinococcosis in dogs. Vet Rec 177, 569 PubMed.
  • Buishi I et al (2005) Reemergence of canine Echinococcus granulosus infection, Wales. Emerg Infect Dis 11 (4), 568-571 PubMed.
  • Lloyd S et al (1998) Use of sentinal lambs to survey the effect of an education programme on control of transmission of Echinococcus granulosus in South Powys, Wales. Bulletin of the World Health Organisation 76 (5), 469-473 PubMed.
  • Cabrera P A, Parietti S, Haran G, Benavidez U, Lloyd S, Perera G, Valledor S, Gemmell M A & Botto T (1996) Rates of reinfection with Echinococcus granulosus, Taenia hydatigena, Taenia ovis and other cestodes in a rural dog population in Uruguay. Intern J Parastol 26 (1), 79-83 PubMed.
  • Lloyd S, Martin S C, Walters T M H & Soulsby E J L (1991) Use of sentinel lambs for early monitiring of the South Powys Hydatidosis Control Scheme - prevalence of Echinococcus granulosus and some other heminths. Vet Rec 129 (4), 73-76 PubMed.

Other sources of information

  • Eckert J et al (2002) WHO/IE Manual on echinococcosis in humans and animals: a public health control. Ed S R Palmer, Lord Soulsby & D I H Simpson. Oxford University Press. pp 689-716. (Comprehensive reveiws of the epidemiology and public health aspects.)
  • www.wales.nhs.uk Hydatid disease (Echinococcosis) background information on hydatid disease and overview of the current situation in Wales.
  • Welsh Assemby Government Website: overview of the current hydatid control programme in Wales, questionnaire for the public, downloadable leaflet and poster.
  • www.esccap.org; website for European Scientific Counsel: Companion Animal Parasites, guidelines for worm control in cats and dogs.
  • Gemmell M A & Roberts M G (1998) Cystic Echinococcosis (Echinococcus granulosus). In: Zoonoses. Biology, clinical practice and public health control Ed. S R Palmer, Lord Soulsby & D I H Simpson. Oxford University Press. pp 665-688.
  • Thompson R C A & Lymbery A J (eds) (1995) Echinococcus and Hyatid Disease.Wallingford, CAB International. pp 477 (Complete overview).
  • Echert J (1998) Alveolar Echinococcosis (Echinococcus multilocularis) and other forms of Echinococcosis (Echinococcus vogeli and Echinococcus oligarthrus). In: Zoonoses. biology, clinical practice and public health control Ed. S R Palmer, Lord Soulsby & D I H Simpson. Oxford university Press. pp 689-716. (Comprehensive reviews of the epidemiology and public health aspects.)


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