In Vitro Cultivation of Plasmodium Falciparum at High Parasitemia

For the routine in vitro cultivation of Plasmodium falciparum, the initial parasitemia is usually adjusted to 1% to 2%. Large quantities of parasites in mature stages are desirable for most biochemical studies. Since only ring stages of the parasites normally appear in the peripheral blood of P. falciparum-infected Aotus monkeys, we have attempted to culture large quantities of parasites to older stages by a modification of the usual in vitro culture methods employed in this laboratory. This modification involves: 1) using moderately high parasitemia in the starting material; 2) addition of TES (N-tris[hydroxymethyl]methyl-2-aminoethansulfonic acid) as a supplementary buffer in our modified Harvard medium; 3) increasing the ratio of blood to culture medium from 1:9 to 1:18; and 4) using 250- and 500-ml flasks as culture vessels. The results obtained in a series of experiments using the modified technique indicate that we can produce mature stages of P. falciparum with parasitemia as high as 75%.