By far the most serious form of the infection, however, is congenital toxoplasmosis, which is acquired by the foetus during a mild infection of the mother. The baby may be stillborn, or it may suffer from hepatosplenomegaly, purpura, jaundice, lesions of the central nervous system, or destroyed areas of the retina. These conditions may be present at birth or may appear weeks or months afterwards. Once tissue has been destroyed - for example, in the brain or the eye - the effects do not regress.
Many species of wildlife and domestic cat and certain other members of the family Felidae are the only hosts in which the parasite will complete the sexual stage of the life cycle. The cat is an important source for the widespread dissemination of the organism in the environment. Infection in cats and other animals is transmitted either by ingestion of oocysts in faeces, in soil, or by consumption of infected animals which have toxoplasma cysts in their tissues. Infection is quite common in cattle, sheep, goats, swine and chickens. Serological surveys in several countries have shown that the average positive reaction rate recorded for the food animal species ranged from 22 to 39%, with sheep being the highest.