Physiological and morphological characters in two pyrimethamine-resistant lines of Plasmodium berghei SP11 after cryopreservation.

The authors describe the characters in two pyrimethamine-resistant lines of Plasmodium berghei berghei SP 11-RR after long storage at very low temperatures. In one case the line had maintained its original virulence but lost its resistance to pyrimethamine. Gametocytogenesis increased and cyclical transmission was successful. Furthermore, parasites crossed the blood-brain barrier and provoked cerebral malaria. In the other case no physiological changes could be detected. The authors conclude that, after cryopreservation, biological behaviour should always be carefully observed.