Kinetics of the invasion and egress processes of Babesia divergens, observed by time-lapse video microscopy.

Based on confocal fluorescence and bright field video microscopy, we present detailed observations on the processes of invasion and egress of erythrocytes by the apicomplexan parasite Babesia divergens. Time-lapse images reveal numerous unexpected findings associated with the dynamics of B. divergens and its ability to manipulate the erythrocyte during both processes in its asexual cycle under in vitro conditions. Despite the speed at which these processes occur and the small size of the parasite, we capture infective merozoites moving vigorously and causing striking deformations in the erythrocyte's plasma membrane during an active invasion. We also observed intraerythrocytic dynamic stages as paired pyriforms, double paired pyriforms, tetrads, unattached pyriform sister cells and multiple parasite stages resulting in the release of large numbers of merozoites over a short period. Of considerable interest is that time-lapse images reveal a novel mechanism of egress used by B. divergens to exit the human erythrocyte. The release occurs when B. divergens parasites establish contacts with the plasma membrane of the erythrocyte from within, before exiting the cell. Visualization and analysis of the images enabled us to obtain useful information and broaden our knowledge of complex and crucial events involved with parasitisation of human erythrocytes by B. divergens.