The visceral lesions in simian malaria with special reference to the splenic reaction

Abstract

A histopathological study of twelve cases of fatal monkey malaria due to infection with P. knowlesi has shown (1) the presence of a vascular mechanism that localizes the parasites in large numbers in the spleen; (2) the presence of a lymphoid reaction in the spleen; and (3) the activation of the reticulo-endothelial system as shown by histiocytic differentiation and active phagocytosis. The severity of the infection appears to be due, not to a failure of the reticulo-endothelial response, but to some other factor which may be the virulence of the parasites for a particular host species. Degenerative swelling of the capillary endothelium with necrosis of the cytoplasmic reticulum around the follicles suggests a toxic factor. Some of the other lesions met with can be explained by the theory of mechanical localization of parasites in the capillaries of the affected part. The lesions met with in monkeys in other organs besides the spleen, suggest that such localizations may be responsible for the varied changes in different organs in human malaria also.