Toxoplasma gondii, the tissue cyst forming coccidium, is one of the polyxenous parasites known to date, which has a facultative heteroxenous life cycle and can infect probably all warm-blooded animals ranging from birds to mammals including human beings. From the zoonotic point of view, T. gondii is one of the most important protozoan parasites causing abortion or a congenital disease in the intermediate hosts.