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Sheep are often kept in an environment that is significantly contaminated with oocysts, and infection follows ingestion of infected food, primarily contaminated pasture. Fields treated with manure or bedding from buildings to which cats have access result in high levels of ovine toxoplasmosis, and insecure storage of supplementary feeds also poses a risk.
 
Sheep are often kept in an environment that is significantly contaminated with oocysts, and infection follows ingestion of infected food, primarily contaminated pasture. Fields treated with manure or bedding from buildings to which cats have access result in high levels of ovine toxoplasmosis, and insecure storage of supplementary feeds also poses a risk.
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Members of the cat family are the definitive hosts of
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As the definitive hosts of ''Toxoplasma gondii'', cats become infected when they hunt and eat infected wild rodents and birds. Between days 3 and 14 post-infection, cats shed over 100 million of oocysts in their faeces. Only 200 oocysts are required to cause abortion in naive pregnant sheep
the parasite and tend to become infected for the first
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time when they start hunting and eating wild rodents
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and birds already infected with T. gondii. Following
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consumption of T. gondii cysts, the parasites excyst
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in the gut of the cat and invade and infect host cells.
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Sexual development of the parasite takes place in the
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gut of the cat resulting in the production of oocysts
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which are shed in the faeces. Shedding usually occurs
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around 3–10 days after initial infection and may
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continue for 2–3 weeks (Dubey and Beattie, 1988).
   
During this period a cat may shed over 100 million
 
During this period a cat may shed over 100 million
 
oocysts and experimental studies in sheep have shown
 
oocysts and experimental studies in sheep have shown
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