In Vitro Culture of Plasmodium Parasites

Because it has been 25 yr since the successful cultivation of Plasmodium falciparum (1 ), most researchers do not remember how difficult it was to work with malaria parasites, especially in vitro. Before the development of current methods, malaria parasite cultures were always short-term, lasting only a few days with decreasing numbers until the parasites died out. Not only was it extremely inconvenient to constantly begin new cultures, but investigators worked with parasites that were abnormal in the sense that the overall population was dying. Sixty-four years passed between the initial studies of Bass and Johns (2 ) and the successful development of continuous cultures of P. falciparum. During that time, many reported advances were able to extend the time of cultivation by only a few days but always with the inevitable terminal results. Most of the early investigators on in vitro cultivation used the bird malaria parasite P. lophurae or the simian parasite P. knowlesi , but the first successful cultivation of any malarial parasite was P. falciparum , the most important of the human malaria species. Using essentially the same procedures, other species of malarial parasites now have been cultured, including P. fragile, P. inui , and P. cynomolgi , but these species offer no real advantages over the use of P. falciparum. Methods for the cultivation of P. vivax have been reported but these cultures apparently require a continuous source of human reticulocytes which limits the suitability and presents a nearly insurmountable barrier to all but a few laboratories (3 ). A recent review of the impact of continuous cultures of P. falciparum underscores the tremendous contributions of this technique on malaria research (4 ).