Cultivation techniques for the erythrocytic stages of malaria parasites.

The study of the biochemistry, physiology, and immunology of plasmodia has been restricted by the difficulty of maintaining the parasites in isolation from the host. Some success has been achieved in cultivating them in vitro, using tissue cultures and chick embryo techniques to study exoerythrocytic states and the sporogonic cycle, but no completely successful method has been found for studying the asexual and sexual stages of plasmodia in circulating red blood cells. The relative slowness with which techniques for continuous in vitro cultivation have been developed is the result of inadequate knowledge of the biochemistry of the parasites and of the blood and its constituents. However, radioactive labelling techniques applied to P. knowlesi cultures are beginning to yield data of fundamental importance. Existing methods for the short-term in vitro cultivation of plasmodia are potentially very useful for analysing malarial antigens, for developing vaccines, and for screening and studying antimalarial drugs. Investigations of the physicochemical requirements for the in vitro preservation of red blood cells are required, and more emphasis should be given to the study of plasmodia with longer cycles. Differences between the metabolism of plasmodia in vivo and in vitro should be studied and the growth factors in normal plasma identified. Studies of the membrane of the parasites and of the red blood cells, of the immune response, and of extracellular methods for the cultivation of plasmodia should be extended.