Echinococcus spp

From Dog
Scolex of E. granulosus from hydatid cyst[1]
Adult E. granulosus[2]
Multiple hydatid cysts removed from a human patient[3]

Echinococcus are a small (1 - 4 mm) parasitic zoonotic tapeworm of dogs and cats found worldwide.

The life cycle of this tapeworm is sustained between a definitive host (foxes[4], dogs, cats, coyotes, wolves and other wild canids) and intermediate herbivore hosts (sheep, cattle, voles, shrews, field mice, etc)[5].

The life cycle involves extra-intestinal migration in the intermediate host (usually sheep or cattle[6]) and formation of an hydatid cyst.

When the dog eats the intermediate host, ingests the hydatid cyst, the protoscolices attach to the small intestinal wall and the worms begin to form proglottids. Gravid proglottids, containing the eggs, detach from the end of the worm and spill their eggs into the lumen of the intestine. The eggs, with characteristic hooks visible on the oncosphere, pass out in the feces. The prepatent period is less than 40 days[7].

Humans get infected by accidental ingestion of eggs from petting, or via fecal contamination of food or utensils. Metacercariae develop into cystic lesions, principally in liver and lungs, after several years[8]. Both canine echinococcosis and human hydatidosis are commonly found in rural farming communities, though there are some reports of human and dog infection in urban areas[9].

Species which have been reported in dogs include:

  • Echinococcus granulosus
  • Echinococcus multilocularis
  • Echinococcus vogeli
  • Echinococcus oligarthrus
  • Echinococcus alveolaris[10]

Most infected dogs are asymptomatic, however cystic hydatid disease does occur, with cyst found in the liver, spleen and sometimes lungs[11]. These cysts become large irregular, fluid-filled masses which grow like a malignant tumor with metastases[12].

A causal link has been associated between echinococcosis and the subsequent development of leukemic T-cell lymphoma in dogs[13].

Diagnosis is based on coprological identification of eggs, but copro-antigen ELISA[14] and species-specific copro-PCR assays are also available for epidemiological surveys[15][16].

Praziquantel is the definitive drug of choice, given at 5 mg/kg via oral or parenteral routes[17], with monthly treatment in endemic regions.

References

  1. Red Orbit
  2. Stanford Uni
  3. IsPub
  4. Murphy TM et al (2012) Freedom from Echinococcus multilocularis: An Irish perspective. Vet Parasitol 190(1-2):196-203
  5. Nonaka N et al (2008) The first instance of a cat excreting Echinococcus multilocularis eggs in Japan. Parasitol Int 57(4):519-520
  6. Tappeh KH et al (2012) Comparison of four methods for DNA extraction from Echinococcus granulosus protoscoleces. Turkiye Parazitol Derg 36(2):100-104
  7. Reperant LA et al (2009) Rodents as shared indicators for zoonotic parasites of carnivores in urban environments. Parasitology 136(3):329-337
  8. Brunetti E & Junghanss T (2009) Update on cystic hydatid disease. Curr Opin Infect Dis 22:497–502
  9. Reyes MM et al (2012) Human and canine echinococcosis infection in informal, unlicensed abattoirs in Lima, Peru. PLoS Negl Trop Dis 6(4):e1462
  10. Stief B & Enge A (2011) Proliferative peritonitis with larval and cystic parasitic stages in a dog. Vet Pathol 48(4):911-914
  11. Brosinski K et al (2012) What is your diagnosis? Peritoneal fluid from a dog with abdominal pain. Vet Clin Pathol 41(2):297-298
  12. Dyachenko V et al (2008) Echinococcus multilocularis infections in domestic dogs and cats from Germany and other European countries. Vet Parasitol 157(3-4):244-253
  13. van Riel A et al (2007) A dog with alveolar echinococcosis: the larval stage of the fox tapeworm. Tijdschr Diergeneeskd 132(21):828-831
  14. Hartnack S et al (2013) Latent-class methods to evaluate diagnostics tests for echinococcus infections in dogs. PLoS Negl Trop Dis 7(2):e2068
  15. Salant H et al (2012) The Development of a Loop-Mediated Isothermal Amplification Method (LAMP) for Echinococcus granulosis Coprodetection. Am J Trop Med Hyg Sep 17
  16. Sherifi K et al (2011) Detection of patent infections of Echinococcus granulosus ("sheep-strain", G1) in naturally infected dogs in Kosovo. Berl Munch Tierarztl Wochenschr 124(11-12):518-521
  17. Tüzer E et al (2010) Efficacy of Praziquantel Injectable Solution Against Feline and Canine Tapeworms. Turkiye Parazitol Derg 34(1):17-20