Canis ISSN: 2398-2942

Ascaridosis

Synonym(s): Ascaridosis; Toxocarosis; Toxascarosis; Roundworm

Contributor(s): Maggie Fisher, Ken Harkin, Peter Irwin

Introduction

  • Cause: ascaridosis includes infection with Toxocara canis and Toxascaris leonina.
  • T. canisis the ascarid most implicated as a zoonosis - cause of visceral larva migrans, ocular larva migrans and covert toxocarosis in humans.
  • Signs: most likely in young pups with a heavy T. canis infection → pot-belly, thin.Occasional intestinal obstruction with heavy burdens.
  • Intestinal ascarid burdens may be present in older dogs but unlikely to be associated with clinical signs.
  • Diagnosis: signs, fecal egg counts.
  • Treatment: anthelmintic.
  • Prognosis: good if appropriate treatment.

Pathogenesis

Etiology

  • Large intestinal burden ofT. canisin the small intestine of pups.

Predisposing factors

General
  • Poor worm control.
  • Endemic high level ofT. canisinfection in dogs and in the kennel environment.

Pathophysiology

  • SeeToxocara canislife cycle Lifecycle Toxocara canis - diagram.
  • 3 main sources of infection for young pups:
    • Transmammary transmission of larvae that have been resting in the bitch's tissues as somatic larvae.
    • Transmission in the milk - normally a minor route accounting for less than 5% of infection unless the bitch was infected in late pregnancy.
    • Embryonated eggs containing L3 larvae (previously considered to be L2) in the nest/run environment.
  • T. canislarvae carry out hepatotracheal migration in pups.
  • Rapidly develop to adult worms in the small intestine.
  • First worms mature by approximately 2.5 weeks of age.
  • Small number of worms well-tolerated.
  • Presence associated with villous atrophy, malabsorption, increased thickness of intestinal muscle layers Toxocara canis.
  • Larger worm burden: pot-bellied appearance and more marked malabsorption, etc.
  • The larger the worm burden the higher the risk of intestinal obstruction or death.
  • Villous atrophy within the small intestine leading to malabsorption Malabsorption.

Timecourse

  • Acute signs may be seen in pups from the time that substantial numbers ofT. canisenter and mature in the intestine.
  • The higher the burden the earlier clinical signs will be seen.
  • Normally unweaned pups (3-8 weeks approximately).
  • Ill-thrift may be seen in pups particularly in this age range.

Epidemiology

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schnieder T, Laabs E M, Welz C (2011) Larval development of Toxocara canis in dogs. Vet Parasitol 175, 193-206 PubMed.
  • Carter C N (1980) Worms also kill. Vet Rec 106 (10), 233 PubMed.
  • Stoye M (1979) Ascarid and hookworm infections in the dog - biology, epizootology and control. Berl Munch Tierarztl Wochenschr 92 (23), 464-472 (Article in German) PubMed.

Other sources of information

  • Deplazes P & Fisher M (2013)ESCCAP -Toxocara2012.Vet Parasitol Special Issue193/4.
  • Holland CV & Smith H V (2006)Toxocarathe enigmatic parasite.CABI Publishing, Wallingford, UK. ISBN 1-84593-026-6.
  • Lewis J W & Maizels R M (1993)Toxocara and toxocariasis - Clinical, epidemiological and molecular perspectives.British Society for Parasitology and the Institute of BiologyISBN 0-900490-30-6.


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