Parasitic tachyzoites (Toxoplasma gondii), light micrograph with fluorescent antibody staining. These organisms are the cause of toxoplasmosis in humans. Cats are the main host but all animals can become infected. Cats excrete oocysts in their faeces, contaminating soil and causing infections. Infection can also occur through ingestion of undercooked meat and by direct contamination. This organism is extremely common worldwide and in most cases can pass without symptoms. However pregnant women are highly susceptible and still birth and congenital deformities can occur.