Canis ISSN: 2398-2942

Toxoplasmosis

Contributor(s): Stephen Barr, Bryn Tennant, SandyTrees, Kerry Simpson

Introduction

  • CauseToxoplasma gondii, a protozoan parasite of the cat; dogs, humans, etc are intermediate hosts.
  • Infection via sporulated oocysts from cat feces, undercooked meat or transplacental.
  • Signs: usually subclinical, occasional severe multisystemic or central nervous system (CNS) infection.
  • Diagnosis: typically based on serology.
  • Treatment: clindamycin, additional drugs.
  • Prognosis: good to fair.

Pathogenesis

Etiology

  • Toxoplasma gondii Toxoplasma gondii : coccidian protozoal parasite.
  • Obligate intracellular parasite.

Predisposing factors

General

  • Cat feces in soil.
  • Undercooked meat.
  • Scavenging/hunting.
  • Feline litter tray if not cleaned daily.

Specific

Pathophysiology

  • Ingestion of sporulated oocysts or tissue cysts → organisms invade and multiply in tissues → intracellular pseudocysts → pseudocysts rupture → release numerous tachyzoites → spread throughout body → chronic phase.
  • Bradyzoites divide slowly within parasitic membrane → tissue cyst, especially in muscles and brain.
  • Once tissue cysts form, host has developed immunity → resistant to re-infection with the same strain.
  • Tissue cysts persist for months/years.

Clinical infection

  • This may occur in:
    • Neonates/puppies.
    • Immunosuppressed individuals (reactivation of chronic infection).
    • Association with canine distemper virus infection Canine distemper disease.
    • Release of organisms from tissue cysts → rapid multiplication of tachyzoites → respiratory/gastrointestinal disease, meningoencephalitis, necrotizing polymyositis, polyneuropathy, polyradiculoneuritis.

Timecourse

  • Initial multiplication in tissues lasts 2-3 weeks.
  • Tissue cysts may persist for months/years.

Epidemiology

  • Definitive hosts are felidae.
  • Intermediate hosts: mammals, amphibians, reptiles, fish.
  • Seroprevalence: cats 40% (0-100%), dogs 30-40%, humans 30-60%.
  • Cats ingest oocysts/tissue cysts → enteroepithelial cycle → shed oocysts within 3 days to 3 weeks → sporulate in environment in 1-5 days → ingested by intermediate host.
  • Dogs infected via:
    • Ingestion of sporulated oocysts from cat feces.
    • Ingestion of meat containing pseudocysts or tissue cysts.
    • Transplacental infection (dam develops parasitemia during pregnancy).

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.
  • Wyrosdick H M, Schaefer J J (2015) Toxoplasma gondii: history and diagnostic test development. Anim Health Res Rev 16 (2), 150-162 PubMed.
  • Dubey J P (2009) The evolution of the knowledge of cat and dog coccidia. Parastiology 136 (12), 1469-1475 PubMed.
  • Cook A J, Gilbert R E, Buffolano W, Zufferey J et al (2000) Sources of toxoplasma infection in pregnant women - European multicenter case control study. BMJ 321 (7254), 142-147 PubMed.
  • Thomas W B (1998) Inflammatory diseases of the central nervous system in dogs. Clin Tech Small Anim Pract 13 (3), 167-178 PubMed.
  • Stiles J, Prade R, Greene C (1996) Detection of toxoplasma gondii in feline and canine biological samples by use of the polymerase chain reaction. Am J Vet Res 57 (3), 264-267 PubMed.
  • Dubey J P (1994) Toxoplasmosis. JAVMA 205 (11), 1593-8 PubMed.

Other sources of information

  • Taboada J & Merchant S R (1995) Protozoal and miscellaneous infections. In:T extbook of Veterinary Internal Medicine. Eds: S J Ettinger & E C Feldman. 4th edn. Philadelphia: W B Saunders. pp 384. (Brief but comprehensive review.)


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