SPOROGONIC DEVELOPMENT OF CULTURED PLASMODIUM-FALCIPARUM IN 6 SPECIESOF LABORATORY-REARED ANOPHELES MOSQUITOS

Sporogonic development of cultured Plasmodium falciparum was compared in six species of Anopheles mosquitoes. A reference species, A. gambia e, was selected as the standard for comparison. Estimates of absolute densities were determined for each lifestage. From these data, four as pects of parasite population dynamics were analyzed quantitatively: 1) successive losses in abundance as parasites developed from gametocyte to ookinete to oocyst stages, 2) oocyst production of sporozoites, 3) correlation between various lifestage parameters, and 4) parasite dis tribution. Parasite populations in A. gambiae incurred a 316-fold loss in abundance during the transition from macrogametocyte to ookinete s tage, a 100-fold loss from ookinete to oocyst stage, yielding a total loss of approximately 31,600-fold (i.e., losses are multiplicative). C omparative susceptibilities in order were A, freeborni much greater th an A. gambiae, A. arabiensis, A. dirus > A. stephensi, A. albimanus. T he key transition(s) determining overall susceptibility differed among species. Despite species differences in oocyst densities and infectio n rates, salivary gland sporozoite production per oocyst (approximatel y 640) was the same among species. The most consistent association amo ng lifestage parameters was a positive correlation between densities a nd infection rates of homologous lifestages. A curvilinear relationshi p between ookinete and oocyst densities in A. gambiae indicated a thre shold density was required for ookinete conversion to oocysts (approxi mately 30 ookinetes per mosquito). The same relationship in A. freebor ni was linear, with no distinct threshold, Ookinete and oocyst populat ions were negative binomially distributed in all species. Indices of h eterogeneity in mosquito susceptibility to infection indicated that ge ne frequencies determining susceptibility fluctuated with time in all species, except A. freeborni where susceptibility remained homogenous throughout the study. This approach provides a framework for identifyi ng mechanisms of susceptibility and evaluating Plasmodium sporogonic d evelopment in naturally occurring vector species in nature.