A scanning electron microscopic study of the sporogonic development of Plasmodium falciparum in Anopheles stephensi.

The full development of Plasmodium falciparum in Anopheles stephensi mosquitoes was studied by scanning electron microscopy. Ookinetic development was described from in vitro cultures. Growing oocysts beneath the basal lamina of the midgut wall mechanically stretch this lamina until it is torn and displaced by day 7. In young oocysts the wall appears smooth. In older oocysts wrinkles in the wall are visible after routine fixation. Osmium tetroxide postfixation greatly reduced the occurrence of these wrinkles. Intracapsular development of sporozoites was visualized after mechanical manipulation of the oocysts during sample preparation. In contrast to P. berghei, no ectopic development was seen in P. falciparum in the mosquito midgut. The mechanism of sporozoite escape from the oocyst appears to be similar to that described for rodent malaria. Fracturing of salivary glands provided the first view by scanning electron microscopy of sporozoites located in proximal and distal gland cells and in the draining duct.