Plasmodium vinckei vinckei, P. v. lentum and P. yoelii yoelii: chronobiology of the asexual cycle in the blood.

The biological rhythms of Plasmodium vinckei vinckei, P. v. lentum and P. yoelii yoelii i.e. synchronicity, duration of the erythrocytic cycle, timing of the schizogony and of the penetration of merozoites into red blood cells, were studied in the Swiss white mouse. Two different methods of synchronisation were used: the freezing-thawing of parasitized blood and the inoculation of a single parasitic stage, separated from the other stages by centrifugation through a Percoll-Glucose gradient. The duration of the schizogonic cycle of P. v. vinckei and P. v. lentum, two highly synchronous subspecies, was 24 hours. With P. v. vinckei the timing of the schizogony was independent of the circadian rhythm of the host and was set by the time of inoculation. With P. v. lentum the timing of the schizogony and merozoites penetration into red blood cells depended both, on the hosts rhythm and the time of inoculation of frozen-thawed blood: schizogony occurred at 18:00 if the inoculum was injected at 06:00 or 12:00 and at 06:00 if injected at 18:00 or 00:01. P. y. yoelii a naturally asynchronous parasite was synchronized by means of a Percoll-Glucose gradient. The duration of its intraerythrocytic cycle was found to be 18 hours, similar to that of the other subspecies of P. yoelii.