What is the life cycle for Toxoplasma (T) gondii?

Updated: Mar 08, 2019
  • Author: Murat Hökelek, MD, PhD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

T gondii has 2 distinct life cycles. The sexual cycle occurs only in cats, the definitive host. The asexual cycle occurs in other mammals (including humans) and various strains of birds. It consists of 2 forms: tachyzoites (the rapidly dividing form observed in the acute phase of infection) and bradyzoites (the slowly growing form observed in tissue cysts).

A cat becomes infected with T gondii by eating contaminated raw meat, wild birds, or mice. The organism’s sexual cycle then begins in the cat’s gastrointestinal (GI) tract. Macrogametocytes and microgametocytes develop from ingested bradyzoites and fuse to form zygotes. The zygotes then become encapsulated within a rigid wall and are shed as oocysts. The zygote sporulates and divides to form sporozoites within the oocyst. Sporozoites become infectious 24 hours or more after the cat sheds the oocyst via feces.


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