Felis ISSN 2398-2950

Toxoplasma gondii

Synonym(s): T. gondii

Contributor(s): Ibulaimu Kakoma

Introduction

Classification

Taxonomy

  • Phylum:Apicomplexa.
  • Class:Sporozoea.
  • Subclass:Coccidia.
  • Order:Eucoccidiidae.
  • Suborder:Eimeriina.
  • Family:Sarcocystidae.
  • Genus:Toxoplasma; single species -Toxoplasma gondii.

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Clinical Effects

Epidemiology

Habitat

  • Definitive host are all species of felids.
  • Intermediate hosts include any mammal or bird.
  • Oocysts are found in the environment.

Lifecycle

  • Felids (definitive hosts) become infected by ingesting animals, usually rodents, infected withT. gondii.
  • Parasites multiply in the intestinal epithelium of cats to produce oocycts in 3-10 days, which are shed in feces.
  • Sporulated oocysts are ingested from the environment by the intermediate host.
  • Tachyzoites spread by the hematogenous route and multiply asexually in cells (the acute phase).
  • Antibody limits the invasiveness of tachyzoites and results in formation of slow-growing cysts containing bradyzoites, usually in muscle cells.

Transmission

  • By ingestion of bradyzoites, tachyzoites or oocysts.
  • Transplacental transmission of tachyzoites (sheep and humans).

Pathological effects

  • Immunosuppression is probably responsible for asymptomatic chronic infection in man.
  • T. gondii has the ability to survive in macrophages which would otherwise kill extracellular organisms. It induces phagocytosis and blocks the delivery of liposomal contents to the vacuole in which it is contained.
  • In the acute form of the disease the organisms enter via the gastrointestinal tract and are disseminated via the lymphatics and portal blood. Multiplication occurs in the tachyzoite form and areas of necrosis occur. Organisms may appear in secretions and excretions and death may occur at this stage. Animal to animal spread does not appear to occur in the acute phase.
  • In the subacute form of the disease the blood and tissues are quickly cleared of tachyzoites by antibodies. The liver, spleen and lungs are also cleared quickly but the brain and heart tend to remain infected until late.
  • Persistence of bradyzoites in cysts occurs in chronic infections. They have been found in pigeons, rats and mice up to 3 years after infection.
  • Strain-specific variation in virulence reported.
  • Prenatally acquired toxoplasmosis more severe than post-natally acquired.

Other Host Effects

  • Most infections with T. gondii are probably asymptomatic.

Control

Control via chemotherapies

Vaccination

  • Vaccines available for sheep.

Other countermeasures

  • Feed cats only dried, canned or cooked food.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Cook A J, Gilbert R E, Buffolano W, Zufferey J et al (2000) Sources of toxoplasma infection in pregnant women - European multicentre case control study. BMJ, 142-147.
  • Burney D P et al (1998) Polymerase chain reaction for the detection of Toxoplasma gondii within aqueous humor of experimentally-inoculated cats. Vet Parasitol 79(3), 181-186.
  • Dubey J P (1998) Advances in the lifecycle of Toxoplasma gondiiInt J Parasitol 28(7), 1019-1024.
  • Dubey J P (1998) Toxoplasma gondii oocyst survival under defined temperatures. J Parasitol 84(4), 862-865.
  • 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, 264-267.

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