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==Introduction==

==Introduction==

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 oocysts in water or food contaminated by cat faeces, although consumption of undercooked meat containing tissue cysts also occurs. Contact with abortion products from infected ewes is 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 from AIDS. If initial infection occurs during pregnancy, or if cysts reactivate at this time, ''Toxoplasma'' may infect the foetus transplacentally. As most mothers are exposed to ''Toxoplasma gondii'' early in life, and are immunocompetent, transplacental infection is seen infrequently. Transmission via blood transfusions or organ transplantation can also occur in man.

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 oocysts in water or food contaminated by cat faeces, although consumption of undercooked meat containing tissue cysts also occurs. Contact with abortion products from infected ewes is 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 from AIDS. If initial infection occurs during pregnancy, or if cysts reactivate at this time, ''Toxoplasma'' may infect the foetus transplacentally. As most mothers are exposed to ''Toxoplasma gondii'' early in life, and are immunocompetent, transplacental infection is seen infrequently. Transmission via blood transfusions or organ transplantation can also occur in man.

==Signalment==

==Signalment==

CNS signs are the most common presentation in immunocompromised patients suffering ''Toxoplasma'' infection or re-activation. Signs are due to intracranial mass lesions or encephalitis, and can include headaches, seizures, pyrexia, coma and focal neurological deficits. Ocular involvement is also possible and usually results from re-activation of a congenital infection. Inflammation of the choroid causes pain and visual disturbances. Occasionally, in severely immunocompromised patients, disease can be seen outwith the CNS and the eye. In these incidences, affected tissues and therefore clinical signs can be variable. For example, patients may suffer pneumonitis, myocarditis, high fevers or polymyositis, which may prove fatal without treatment.

CNS signs are the most common presentation in immunocompromised patients suffering ''Toxoplasma'' infection or re-activation. Signs are due to intracranial mass lesions or encephalitis, and can include headaches, seizures, pyrexia, coma and focal neurological deficits. Ocular involvement is also possible and usually results from re-activation of a congenital infection. Inflammation of the choroid causes pain and visual disturbances. Occasionally, in severely immunocompromised patients, disease can be seen outwith the CNS and the eye. In these incidences, affected tissues and therefore clinical signs can be variable. For example, patients may suffer pneumonitis, myocarditis, high fevers or polymyositis, which may prove fatal without treatment.

When infection is acquired for the first time during pregnancy, congenital toxoplasmosis can arise. This may also occur if a mother infected before conception becomes immunosuppressed during pregnancy. Foetuses infected congenitally may be aborted, stillborn, or born with toxoplasmosis. Infections later in gestation are more likely to give rise to a live but infected neonate. When neonates are born with toxoplasmosis disease can be severe, particularly if transplacental infection occured early in pregnancy. Signs can include rashes, icterus and hepatosplenomegaly as well as retinochoroiditis, cerebral calcifications, hydrocephalus/microcephaly, and psychomotor retardation. These last four signs together are characteristic of congenital toxoplasmosis. Infants infected during the third trimester are less severely affected and tend to appear normal at birth. However, signs may develop months to years later, and can include seizures, retinochoroiditis and intellectual disability.

When infection is acquired for the first time during pregnancy, congenital toxoplasmosis can arise. This may also occur if a mother infected before conception becomes immunosuppressed during pregnancy. Foetuses infected congenitally may be aborted, stillborn, or born with toxoplasmosis. Infections later in gestation are more likely to give rise to a live but infected neonate. When neonates are born with toxoplasmosis disease can be severe, particularly if transplacental infection occurred early in pregnancy. Signs can include rashes, icterus and hepatosplenomegaly as well as retinochoroiditis, cerebral calcifications, hydrocephalus/microcephaly, and psychomotor retardation. These last four signs together are characteristic of congenital toxoplasmosis. Infants infected during the third trimester are less severely affected and tend to appear normal at birth. However, signs may develop months to years later, and can include seizures, retinochoroiditis and intellectual disability.

==Laboratory Tests==

==Laboratory Tests==

==Links==

==Links==

*[http://www.cdc.gov/toxoplasmosis/ Center for Disease Control and Prevention: Toxoplasmosis Factsheets]

*[http://www.cdc.gov/toxoplasmosis/ Center for Disease Control and Prevention: Toxoplasmosis Factsheets]

*[http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1195733799638 Health Protection Agency: Toxoplasmosis]

*[http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1195733799638 Health Protection Agency: Toxoplasmosis]

==References==

==References==

[[Category:Zoonoses]]

[[Category:Zoonoses]]

[[Category:To_Do_-_Review]]

[[Category:Expert_Review]]