Toxoplasmosis Life Cycle Flashcards
What protozoan parasite causes toxoplasmosis?
Toxoplasma gondii (an apicomplexan)
What is T. gondii’s reservoir?
A bradyzoite (cyst) in many animals and birds
What is T. gondii’s definitive host?
Cat (sheds oocysts from intestinal stage)
What are the modes of transmission of T. gondii?
Faecal-oral from cat (oocysts from faeces)
Oral (bradyzoite cysts in raw meat)
Transplacental during acute infection
Sexually transmitted? male–> female (tachyzoites present in seminal fluid)
Draw zoonosis stage of life cycle
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Draw life cycle of T. gondii infection
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Why do domestic cats <1yrs excrete the most oocysts?
They haven’t had time to develop an immunity
Describe the life cycle of T. gondii in the human host
Sporozoite invasion of gut epithelial macrophages results in proliferation of the parasites within the macrophage
When mature, the macrophage releases tachyzoites which will invade other macrophages and tissue cells
The invasion of host cells by T. gondii is parasite-driven and needs actin-based motility of the parasite, rather than the host cell cytoskeleton i.e. it’s not taken up by phagocytosis
Also there is no fusion of the parasitophorous vacuole with lysosomes, which means it survives in the host immune cell
It is then carried in the blood stream to other tissue cells which the tachyzoites invade
In tissue cells, the parasite can encyst and proliferate forming numerous bradyzoites which are infective if ingested by a predator
The parasite has a particular tropism for brain tissue
What are tachyzoites?
Intracellular parasites. Are pear-shaped organisms enclosed in a parasite membrane to form a cyst
Who is most at risk of toxoplasmosis?
Immunodeficient individuals and unborn babies
What is meant by the extended phenotype?
Parasitic manipulations of host physiology or behaviour to aid transmission
Why do some European countries have a higher T. gondii prevalence than others?
Countries where raw meat is popular have a higher prevalence than other countries e.g. in France, as much as half of the population may be infected
