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→Transmission to Sheep
When sheep ingest oocysts, ''T.gondii'' intiates extraintestinal replication. This process is the same for all hosts, and also occurs when carnivores ingest tissue cysts in other animals. Sporozoites (or bradyzoites, if cysts are consumed) are released in the intestine to infect the intestinal epithelium where they replicate. This produces tachyzoites, which reproduce asexually within the infected cell. When the infected cell ruptures, tachyzoites are released and disseminate via blood and lymph to infect other tissues. Tachyzoites then replicate intracellularly again and the process continues until the host becomes immune or dies. If the infected cell does not burst, tachyzoites eventually encyst as bradyzoites and persist for the life of the host. Cyst are most commonly found in the brain or skeletal muscle, and are a source of infection for carnivorous hosts.
When sheep ingest oocysts, ''T.gondii'' intiates extraintestinal replication. This process is the same for all hosts, and also occurs when carnivores ingest tissue cysts in other animals. Sporozoites (or bradyzoites, if cysts are consumed) are released in the intestine to infect the intestinal epithelium where they replicate. This produces tachyzoites, which reproduce asexually within the infected cell. When the infected cell ruptures, tachyzoites are released and disseminate via blood and lymph to infect other tissues. Tachyzoites then replicate intracellularly again and the process continues until the host becomes immune or dies. If the infected cell does not burst, tachyzoites eventually encyst as bradyzoites and persist for the life of the host. Cyst are most commonly found in the brain or skeletal muscle, and are a source of infection for carnivorous hosts.
==Transmission to Sheep==
===Oocysts in the Environment===
Infected cats shed oocysts continuously between days 3 and 14 post-infection. During this time, hundreds of millions of oocysts may be shed. The main sources of feline toxoplasma infection are chronically infected birds and rodents. Rodents are particularly important since they can pass ''T. gondii'' infection to their offspring without causing clinical disease. This means that a farm may develop a reservoir of ''T. gondii'' tissue cysts with the potential to cause feline infection and massive oocyst excretion. In turn, environments may easily become contaminated with a high oocyst burden when a cat is introduced.
Infected cats shed oocysts continuously between days 3 and 14 post-infection. During this time, hundreds of millions of oocysts may be shed. The main sources of feline toxoplasma infection are chronically infected birds and rodents. Rodents are particularly important since they can pass ''T. gondii'' infection to their offspring without causing clinical disease. This means that a farm may develop a reservoir of ''T. gondii'' tissue cysts with the potential to cause feline infection and massive oocyst excretion. In turn, environments may easily become contaminated with a high oocyst burden when a cat is introduced.
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.
Members of the cat family are the definitive hosts of
Members of the cat family are the definitive hosts of
the parasite and tend to become infected for the first
the parasite and tend to become infected for the first
there is widespread environmental contamination
there is widespread environmental contamination
with T. gondii oocysts (Dabritz et al. 2007).
with T. gondii oocysts (Dabritz et al. 2007).
Congenital transmission
===Congenital Transmission===
Primary infection during pregnancy. As sheep are
Primary infection during pregnancy. As sheep are
not carnivores, consumption of tissues infected with
not carnivores, consumption of tissues infected with
may occur as a result of recrudescence of an
may occur as a result of recrudescence of an
endogenous infection (Trees and Williams, 2005).
endogenous infection (Trees and Williams, 2005).
Recrudescence of an endogenous infection. While recrudescence
===Recrudescence of Endogenous Infection===
While recrudescence
of a persistent endogenous infection is
of a persistent endogenous infection is
a very common route of congenital infection with
a very common route of congenital infection with