Formation of merozoites in intraerythrocytic Babesia microti: an ultrastructural study

Abstract

Babesia microti used in this study derives from a human infection and has been maintained in hamsters by intraperitoneal injections of infected blood. The parasite is covered by a single membrane and lies free in the cytoplasm of erythrocytes. It forms numerous pseudopods extending in all directions and to follow the events of merozoite formation it was necessary to resort to serial sections. Through this method it was found that the number of merozoites produced simultaneously by a single parasite is not more than four, and that a large chunk of the nucleus and the cytoplasm remains still available for further reproduction. Each merozoite after pinching off from the parent becomes an independent organism able to leave the host cell. The nucleus divides by budding and the buds retain their connection with the main body of the nucleus until the very end when the merozoite pinches off from the parent cell. This is budding sensu stricto. Since nuclear division does not precede cytoplasmic fission, Babesia is lacking the schizogony stage. The structure of merozoites appears to be much simpler than in other Sporozoa and a number of organelles at the anterior end are missing.