Gametocytogenesis by malaria parasites in continuous culture

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Abstract
Asexual proliferation of malaria parasites proceeds by multiplication of the parasites within red cells. Following rupture of the host cells the released merozoites re-invade other red cells. On re-invasion, a proportion of merozoites become, not asexual parasites but gametocytes, the sexual stages infective to the mosquito vectors. Conversion of asexual parasites to gametocytes occurs not only during natural infections but also in continuous in vitro culture as reported first by Trager and Jensen1–4 and by others5,6. We showed previously that the proportion of early intra-erythrocytic stages (ring stages) of Plasmodium falciparum which developed into gametocytes in culture was influenced by culture conditions7. Gametocyte formation was rare in conditions supporting rapid proliferation but frequent when parasite densities were static. We now show that nearly 100% of ring stages develop into gametocytes in response to 1 mM cyclic AMP in static cultures whereas in rapidly growing cultures few rings become gametocytes in response to cyclic AMP.