False colour transmission electron micrograph of the trophozoite, or proliferative form, of the sporozoan Toxoplasma gondii. Several organisms (large central ovals) are seen in liver tissue. 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: x3,600 at 6x4.5cm size.