[Ultrastructural observation on the oocyst development and sporozoite formation of Plasmodium vivax]

The oocyst development of Plasmodium vivax was heralded by the appearance of cytoplasmic vacuoles and membraneous clefts. These clefts broke up oocyst cytoplasm into many sporoblasts. The onset of transformation from oocyst to sporozoite was heralded by forming pellicular complex, at some point of pelliculum of sporoblast dense inner membrane and subpellicular microtubules formed beneath the plasmalemma. The pellicular complex bulged out to form sporozoite buds appearing as small domes. Following enlargement of sporozoite buds the apical ends of the buds became conical in longitudinal sections with the newly formed apical rings at their truncated apices and then, newly formed dense inner membranes and subpellicular microtubules gradually extended backwards and finally enclosed the sporozoites. Beneath the inner membrane there were a total of 10-12 subpellicular microtubules arranged irregularly as 5 + 6, 6 + 5, 6 + 6, 7 + 4, 8 + 3, 10 + 1 and 11 + 1. During the formation of sporozoite, intranuclear spindle appeared in the nucleus, suggesting that the second meiosis in the life cycle of Plasmodium vivax occurred in developing sporozoites.