Plasmodium berghei: characteristics of a selected population of small free blood stage parasites.

The characteristics of a selected population of small blood stage parasites obtained by differential centrifugation of a population of P. berghei parasites freed by continuous flow sonication are described. About 10% of these free parasites are merozoites, many others are transitional forms having some merozoite characteristics. The parasite preparations are infectious and sufficiently resistant to incubation at 37 degrees C to be useful experimentally. Disc gel electrophoresis analysis indicates that these small parasites differ in composition from an unselected intraerythrocytic P. berghei population.