Toxoplasma parasites. Coloured transmission electron micrograph (TEM) of Toxoplasma gondii parasites inside a human cell. T. gondii is a species of parasitic protozoa that can be carried by all known mammals. It causes toxoplasmosis, a usually minor and self-limiting disease. It can, however, have serious or even fatal effects on an unborn foetus if the mother contracts toxoplasmosis during pregnancy. Magnification: x9160 when printed 10 centimetres wide.