False-colour transmission electron micrograph of the trophozoite, or proliferative form, of the sporozoan Toxoplasma gondii. They appear as the large dark stained bodies enclosing numerous organelles. T. gondii causes toxoplasmosis in humans & is especially dangerous to pregnant women. Cats are the definitive host and all mammals including sheep & cattle may become infected. Only cats excrete the oocysts in their faeces, which contaminate the soil & cause the infection in humans & animals. Infection in man also occurs through undercooked meat, or direct contact. Magnification: x3000 at 35mm size.