What is the morphology of oocysts of toxoplasma gondii?

Answer 1

Cellular stages

Fixed T. gondii tachyzoites visualized with immunofluorescence

During different periods of its lifecycle, individual parasites convert into various cellular stages, with each stage characterized by a distinct cellular morphology, biochemistry, and behavior. These stages include the tachyzoites, merozoites, bradyzoites (found in tissue cysts), and sporozoites (found in oocysts).

Tachyzoites

Motile, and quickly multiplying, tachyzoites are responsible for expanding the population of the parasite in the host.[

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When a host consumes a tissue cyst (containing bradyzoites) or an oocyst (containing sporozoites), the bradyzoites or sporozoites stage-convert into tachyzoites upon infecting the intestinal epithelium of the host.[

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During the initial, acute period of infection, tachyzoites spread throughout the body via the blood stream.[

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During the later, latent (chronic) stages of infection, tachyzoites stage-convert to bradyzoites to form tissue cysts.Merozoites

An unstained T. gondii tissue cyst, bradyzoites can be seen within

Like tachyzoites, merozoites divide quickly, and are responsible for expanding the population of the parasite inside the cat intestine prior to sexual reproduction.[

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When a feline definitive host consumes a tissue cyst (containing bradyzoites), bradyzoites convert into merozoites inside intestinal epithelial cells. Following a brief period of rapid population growth in the intestinal epithelium, merozoites convert into the noninfectious sexual stages of the parasite to undergo sexual reproduction, eventually resulting in the formation of zygote-containing oocysts.[

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Bradyzoites

Bradyzoites are the slowly dividing stage of the parasite that make up tissue cysts. When an uninfected host consumes a tissue cyst, bradyzoites released from the cyst infect intestinal epithelial cells before converting to the proliferative tachyzoite stage.[

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Following the initial period of proliferation throughout the host body, tachyzoites then convert back to bradyzoites, which reproduce inside host cells to form tissue cysts in the new host.Sporozoites

Sporozoites are the stage of the parasite residing within oocysts. When a human or other warm-blooded host consumes an oocyst, sporozoites are released from it, infecting epithelilal cells before converting to the proliferative tachyzoite stage.[

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