A comparative study on the ultrastructure of plasmodium sporozoites within the oocyst and salivary glands, with particular reference to the incidence of the micropore

The ultrastructure of sporozoites of 5 species of malaria parasites, Plasmodium vivax, P. cynomolgi, P. gallinaceum, P. berghei nigeriensis and P. vinckei chabaudi has been studied both in the o6cyst and the salivary gland of the mosquito. Micropores were readily found in both situations in P. vivax, P. cynomolgi and P. gallinaceum, but none were detected in the rodent species. Usually only 1 micropore was seen in the sporozoite; 2 micropores were seen in single sporozoites of P. cynomolgi, and on one occasion 6 were seen on the surface of the maturing sporoblastoid in P. vivax. Sections of 2,000 sporozoites were examined in each group, the incidence of the micropore was rather over 1%, though it reached 5% in sporozoites of P. cynomolgi in the salivary gland. There was little difference in the incidence of the micropore between the oöcyst and salivary gland. The possible relationship between the absence of a micropore in the sporozoites of the rodent species and the well known poor infectivity of these parasites is discussed.