Variations in structure and function during the life cycle of malarial parasites.

The fine structure of malarial parasites is reviewed and the function of the intracellular organelles is discussed. When the erythrocytic, exoerythrocytic, and mosquito stages of plasmodia are compared, substantial differences are seen. The major differences involve the amount of surface coat of the motile forms, the structure and function of the mitochondria, and the ingestion and digestion of nutrients. Significant structural differences are also observed between comparable stages of mammalian and avian parasites. These differences indicate that malarial parasites adapt themselves to the different environments in which the parasite resides.When host cell changes induced by malarial parasite infection are reviewed, alterations characteristic of the infecting plasmodia are observed in erythrocytes. Erythrocyte changes include caveola-vesicle complexes, excrescences, and clefts. The caveola-vesicle complexes possess malarial antigens and exhibit pinocytotic activities. The excrescences form focal junctions with adjacent cells and may be responsible for infected erythrocyte sequestration in organs. The significance of these host cell changes specific to certain species of malarial parasite is still unknown.