Toxoplasma gondii--an environmental contaminant.

Toxoplasma gondii, the causal agent of toxoplasmosis, is a ubiquitous protozoan parasite which has the potential to infect man and all warm-blooded animals. It has as its definitive host the cat. Infections acquired by the human adult are generally subclinical. However, if acquired for the first time during pregnancy, the parasite can invade the developing foetus. Under these circumstances infection can result in abortion, stillbirth or production of live-born offspring with severe multiple organ involvement. Alternatively, offspring can be symptomless at birth but may manifest neurological and ocular sequelae of toxoplasmosis in later life. The degree of clinical involvement is thought to be dependent upon the time of acquisition of infection by the pregnant female. Recent investigations have been concerned with behavioural aspects of predator-prey relationships between cats and rodents. Since these aspects affect the spread of toxoplasmosis in the environment, they have strong epidemiological and ecological implications. Toxoplasma infection in the environment, they have strong epidemiological and ecological implications. Toxoplasma infection in mice is associated with subtle alterations in exploratory behaviour which are almost certainly maladaptive, rendering infected mice more susceptible to predation by cats. Consequently the behavioural abnormalities in mice associated with Toxoplasma infection would be of major importance for the continuation of the life-cycle of the parasite. Ingestion of Toxoplasma-infected mice leads to oocyst production in cats and this opens up the well-known pathway whereby Toxoplasma infection reaches the human species.