Sporozoite invasion of Plasmodium berghei, rodent malaria parasite, to the salivary glands of the vector mosquito, Anopheles stephensi: an electron microscopic study.

The sporozoite penetration process of a rodent malaria parasite, Plasmodium berghei, into the salivary glands of the vector mosquito, Anopheles stephensi and sporozoite distribution in the cytoplasm and secretory cavity in the distal region of salivary glands were observed with a scanning electron microscope and a transmission electron microscope. In noninfected mosquitoes, many swellings were observed on the outer surface of the median lobes of salivary glands, whereas many shallow depressions were observed on the lateral lobes. In infected mosquitoes, sporozoites were concentrated on the distal region of median and lateral lobes of salivary glands and penetration occurred from the anterior end into both lobes. Sporozoites were about 10 μm long with one end flat and the other round. Small holes through which sporozoites might have passed were observed on the surface of both median and lateral lobes. A white powder like substance, which might come from the holes, covered the surface of both lobes. Sporozoites invading the cytoplasm of the salivary gland cells were surrounded with vacuoles. These sporozoites invaded the secretory cavity and lodged to form bundles.