The ultrastructure of cultured Plasmodium gallinaceum ookinetes: a comparison of intact stages with forms damaged by extracts from blood fed, susceptible Aedes aegypti.

The ultrastructure of intact, mature and immature ookinetes of Plasmodium gallinaceum is compared with corresponding stages which have been damaged by Aedes aegypti extracts prepared during blood digestion. The study reveals some new details of ookinete ultrastructure. In particular the composition, development and mode of formation of the pellicle of plasmodial ookinetes is shown to be similar to that of other sporozoans. The pellicle is composed of three membranes, develops in the growing protrusion of the retort-shaped early ookinete and its inner layer is probably formed by fusion of peripheral vesicles. Staining with ruthenium red indicates the presence of a surface coat. Furthermore Golgi-like structures and lysosomes can be observed. After exposure to A. aegypti extracts the parasites exhibit signs of severe cell damage and degeneration, such as disintegration and vacuolization of the cytoplasm. Damage of the plasma membrane is demonstrated by its permeability for ruthenium red. Cell damage is particularly prominent in those cell parts which are not covered by the pellicle and therefore suggests a protective function for this structure.