ISSN 2398-2977      

Toxoplasma gondii


Susan Dawson

Synonym(s): T. gondii




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


  • Gr:toxon- bow;plasma- mold, image, formation.

Active Forms

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Clinical Effects



  • Definitive host is the cat.
  • Intermediate hosts include any mammal or bird.
  • Oocysts are found in the environment.


  • Cats ingest infected intermediate host, usually rodents, containing tissue tachyzoites or bradyzoites   →   oocysts produced in feline intestine in 3-10 days   →   shed in feces   →   ingested by intermediate host   →   sporozoites penetrate intestinal wall   →   hematogenous spread of tachyzoites   →   cysts containing bradyzoites.


  • 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. gondiihas 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. Death may occur at this stage. Animal to animal spread does not occur in the acute phase.
  • In the subacute form of the disease blood and tissues are quickly cleared of tachyzoites by antibodies. The liver, spleen and lungs are also cleared quickly but the brain and heart are cleared 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.
  • Some strains are more virulent than others.
  • Prenatally acquired toxoplasmosis more severe than post-natally acquired.

Other Host Effects

  • Most infections withT. gondiiare probably asymptomatic.


Control via chemotherapies

  • Pyrimethamine with trimethoprim/sulfonamides drugs   Trimethoprim  or clindamycins .


  • Vaccines available for sheep.

Other countermeasures

  • Feed cats only dried, canned or cooked food.


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Further Reading


Other sources of information

  • Recent references from PubMed and VetMedResource.
  • Turner C B and Savva D (1991) Detection of Toxoplasma gondii in equine eyes. Vet Rec 129 (6), 128 PubMed.
  • Turner C B & Savva D (1990) Evidence of Toxoplasma gondii in an equine placenta. Vet Rec 127 (4), 96 PubMed.

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