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When man or another animal ingests oocysts or tissue cysts, ''T. gondii'' intiates extraintestinal replication. This process is the same for all intermediate hosts, although the form ingested depends on diet. Sporozoites (from oocysts) or bradyzoites (from tissue cysts) 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, most commonly in the brain or skeletal muscle.  

When man or another animal ingests oocysts or tissue cysts, ''T. gondii'' intiates extraintestinal replication. This process is the same for all intermediate hosts, although the form ingested depends on diet. Sporozoites (from oocysts) or bradyzoites (from tissue cysts) 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, most commonly in the brain or skeletal muscle.  

Human exposure to toxoplasmosis is common: it is estimated that aroung 60% of healthy adults worldwide are seropositive to ''Toxoplasma gondii''. The most common route of human infection is ingestion of oocyts in water or food contaminated by cat faeces, although consumption of undercooked meat containing tissue cysts also occurs. An immune response occurs in response to infection, and tissue cysts form in several organs. These cysts may later reactivate in immunocompromised patients, for example those suffering AIDs. If initial infection occurs during pregnancy, or if cysts reactivate at this time, ''Toxoplasma'' may infect a foetus transplacentally. As most mothers are exposed to ''Toxoplasma gondii'' early in life, and are immunocompetent, transplacental infection is seen infrequently. In man, blood transfusions and organ trasplantation can also occur.  

Human exposure to toxoplasmosis is common: it is estimated that aroung 60% of healthy adults worldwide are seropositive to ''Toxoplasma gondii''. The most common route of human infection is ingestion of oocyts in water or food contaminated by cat faeces, although consumption of undercooked meat containing tissue cysts also occurs. Contact with abortion products from infected ewews is also a risk for pregnant women. An immune response occurs in response to infection, and tissue cysts form in several organs. These cysts may later reactivate in immunocompromised patients, for example those suffering AIDs. If initial infection occurs during pregnancy, or if cysts reactivate at this time, ''Toxoplasma'' may infect a foetus transplacentally. As most mothers are exposed to ''Toxoplasma gondii'' early in life, and are immunocompetent, transplacental infection is seen infrequently. In man, transmission via blood transfusions or organ transplantation can occur.  

Despite the various methods of transmission to man, and the high seroprevalence to ''Toxoplasma gondii'', the risk of developing cloinical disease is low and is generally restricted to foetuses infected ''in utero'', and immunosuppressed patients.

Despite the various methods of transmission to man, and the high seroprevalence to ''Toxoplasma gondii'', the risk of developing cloinical disease is low and is generally restricted to foetuses infected ''in utero'', and immunosuppressed patients.