Observation of the in vitro production of male gametes of the human malaria parasite Plasmodium falciparum through the process of exflagellation

Exflagellation is the term given to the production of male gametes by sporozoans, in particular the Plasmodium parasite that causes malaria in a wide range of vertebrates including humans. In the malaria life cycle this key event occurs naturally within the midgut of a female Anopheles mosquito a few minutes after it takes a blood meal infected with Plasmodium gametocytes. This phenomenon also happens spontaneously in vitro and thus may be observed in cultures of fresh parasitized blood under the light microscope (1000 x magnification under oil immersion). We report the rare observation in vitro of male (micro)gametogenesis by the major human malaria parasite P. falciparum. While this process may be recorded by video, by which its explosively energetic nature can readily be appreciated, it is not straightforward to capture by still photography because the parasite oscillates vigorously and thus moves continually in and out of the microscope’s two-dimensional plane of focus.