Experimental toxoplasmosis in chimpanzees

Toxoplasmosis: comparative species susceptibility and host immune response

The protozoan parasite Toxoplasma gondii is capable of infecting all warm blooded animals; however, the consequences of infection are very variable between different species of animal. Marsupials and New World monkeys, which have evolved largely separately from the cat, the definitive host of the parasite, are among the most vulnerable species where infection with T. gondii can prove fatal. In more resistant species such as humans and sheep, infection is generally unapparent, provoking only mild symptoms; thereafter the host remains infected for life. However, when the immune system is compromised, such as in the immunologically immature fetus, infection with the parasite can have very serious consequences. Much of the work examining host immune responses has been done using experimentally infected mice. While there are many advantages in using this experimental model, care should be taken in extrapolating results from mice to other species. Mice are extremely vulnerable to the consequences of infection with T. gondii., and their use to further our understanding of congenital toxoplasmosis may not be ideal, as fetal infection can occur in successive pregnancies. This is not the case in rats or sheep; they are more resistant to the disease and therefore may provide a more relevant model for human congenital toxoplasmosis. Studies of host immune responses have emphasised the importance of the cytokine interferon gamma (IFN gamma) in resistance to T. gondii. The efficiency of induction of this cytokine may be critical for determining the outcome of the host-parasite relationship.

An epidemic of toxoplasmosis in a captive colony of squirrel monkeys (Saimiri sciureus)

An epidemic of acute, disseminated toxoplasmosis caused 30 per cent mortality and an apparent 100 per cent morbidity in a captive colony of squirrel monkeys (Saimiri sciureus). The source of the infection could not be elucidated. Although most deaths were due to pulmonary oedema, one monkey probably died of heart and liver failure. These findings support the view that New World monkeys are unusually sensitive to Toxoplasma gondii infection. The similarity of the disease in these monkeys with that in immunocompromised human beings is an observation worthy of further investigation.

Intestinal coccidiosis in a patient with alpha-chain disease

During an ultrastructural study of small-intestinal mucosa from a patient suffering from alpha-chain disease organisms were identified within the epithelial cytoplasm which showed the fine structural features of the coccidian group. Though coccidiosis is well recognized as causing a diarrhoeal and often lethal illness in animals it has been neglected as a cause of disease in man. Thus this finding may be significant and warrants further investigation into its possible role in the pathogenesis of alpha-chain disease.