The pathophysiology of Babesia rodhaini infection in intact rats and B.divergens infection in splenectomized calves has been examined. In both infections the anaemia and the pathological changes recorded were closely related to the parasite development and once the parasitaemia declined recovery was apparent.
The roles of the spleen and the reticulo -endothelial system as possible mechanisms of erythrocyte loss in B.rodhaini infections were examined and while this organ and system were responsible for some loss of erythrocytes their contribution to the anaemia was considered to be small.
In both infections the osmotic fragility of the erythrocytes was significantly increased. Studies of B.rodhaini and B.divergens in living blood preparations showed very different modes of parasite activity within erythrocytes but both parasites appeared to maintain a close association with the erythrocyte membrane. The scanning electron microscope revealed considerable morphological alterations on the surface of B.rodhaini -infected erythrocytes and during severe babesiosis in rats the morphological characteristics of the entire erythrocyte population were greatly changed. It was concluded that the anaemia of babesiosis was due not only to the destruction of erythrocytes but probably also to a loss in efficiency of surviving cells.
The serum biochemical and histopathological changes found in both infections were first recorded after the appearance of parasites in the peripheral circulation. The disease in rats was consistently severe while the disease in calves varied in severity. In general the
changes recorded were non -specific and common to other disease states.
A coagulation disturbance leading to thrombosis and frequent splenic infarction was found in rats during B.rodhaini infection. Thrombocytopenia, hyperfibrinogemaemia d raised serum levels of fibrinogen or fibrin degradation products were present from early in infection and these changes were considered to be manifestations of a disseminated intravascular coagulation syndrome. In calves a thrombocytopenia, minor changes in plasma fibrinogen levels and positive protamine paracoagulation tests were found during the course of B.divergens infection. From this evidence, and from reviewing the literature on the pathology of babesiosis, it was concluded that disseminated intravascular coagulation could be an important mechanism in the pathogenesisof babesiosis.