An electron microscopic study of intravascular agglutination in the cerebral cortex due to Babesia argentina infection

The progressive changes in brain capillaries of calves infected with Babesia argentina are described. Initially, the parasitaemia was low (about 5 per cent) and infected red cells had an essentially normal appearance. Terminally, the parasitaemia was > 90 per cent and by this time infected cells were stellate in appearance, connected by fine strands to other infected cells, and to the capillary endothelium which also showed pathological changes. Uninfected cells appeared normal at all stages of the infection. In severe cases most infected cells were haemolysed. The presumed stickiness of infected cells was probably due to changes in the erythrocyte membrane. Parasites were larger than normal and usually possessed two or three nuclei, containing aggregations of chromatin