Toxoplasma gondii causes the disease toxoplasmosis. T. gondii is a small parasite and very commonly infects humans. It is acquired from stages of the parasite that persist in a latent encysted form in meat and when a stage of the parasite that is excreted by members of the cat family contaminates the environment and humans or other animals ingest them. An acutely infected cat excretes 20 million oocysts of the parasite over about two weeks. Even one is infectious. The oocyst can remain infectious in warm moist soil for up to a year and in water for up to six months.
The parasite causes eye and brain damage in a baby, if untreated, when a mother is infected for the first time while pregnant and passes the parasite to her child. The incidence of such congenital infection varies with locale and is not well- defined. For example, congenital infection is estimated to affect approximately 1 in 5000 babies born in the US, 1 in 3000 born in France, and 1 in 300 born in Panama.
The acute infection in older children and adults may be without symptoms, cause flu like illness or enlarged lymph nodes. Eye disease or destruction of other tissues by the parasite, such as infection and inflammation of the heart or brain, occurs in some older children and adults who acquire the infection. However, these manifestations are not frequent.
This latent parasite occurs very commonly in people, infecting approximately a third of all humans, or approximately 2 billion people worldwide. This latent parasite can cause disease if a person becomes immune compromised from conditions such as malignancies, autoimmune diseases, AIDS, and transplantation and their treatments. It can also recrudesce and cause later eye disease in congenitally infected children and in some older children and adults who acquired the parasite after birth. The effect of a chronic brain infection in 2 billion people, or some of them who might by genetically susceptible to a more extensive inflammatory process on subsequent neurodegenerative diseases, is unknown.
Treatment can prevent transmission of the parasite from mother to child as well as treat and prevent adverse consequences of the infection if diagnosed and treated early.