Penetration of the mosquito midgut wall by the ookinetes of Plasmodium yoelii nigeriensis.

The penetration route of ookinetes of Plasmodium yoelii nigeriensis in the midgut of a mosquito, Anopheles omorii, was investigated by electron microscopy. Within 15-18 h after an infective blood meal, ookinetes could be seen in the midgut lumen, in the process of entering the midgut wall, or lodged between the basement membrane and the basal lamina. The morphology of the ookinetes and their transformation into early oocysts were found to be similar to those previously reported. Ookinetes penetrated the midgut wall by the intercellular route; however, the intracellular occurrence of the parasite was also observed. Vacuoles appeared around the penetrating ookinetes during the penetration process, but no change in the electron density of the rhoptry-microneme complex was noted.