[Study of gametocytes from the Plasmodium "vivax" group: morphology, development in Anopheles and infectivity of Plasmodium yoelii microgametocytes].

The study of the gametocytes of Plasmodium yoelii enabled the differentiation of 4 morphological types: O, I, II and III (in a chronological order) and amongst each of these types the differentiation of healthy and altered gametocytes. These morphological data represent a tool for investigations on the biology of the gametocytes of the "vivax" group. Preliminary experiments bring informations on the evolution of gametocytes and the mechanisms of their infectivity. 1--In experimentaly infected white mice gametocytes of P.y. nigeriensis are infective up to the 3rd-4th day, those of P. y. yoelii until the 5th-6th days. These periods can be shorter when the infection is very virulent or longer when chronical. 2--The drop in infectivity coincides with the increase in number of the altered gametocytes. 3--The loss of infectivity is connected with the condition of the blood: when parasitaemiae are high, it becomes rapidly unsuitable to a normal evolution of the gametocytes: thus, non infective gametocytes acquire a good infectivity in less than two hours when transfered to a clean mouse. 4--The gametocytic composition of the blood taken up by the Anopheles in the capillaries can be very different from that taken at the tail of a Rodent. In the young parasitaemiae, when the Rodents are most infective to the Mosquitoes, there is a considerable enrichment in gametocytes O-I of the blood ingested by the Anopheles as compared to that taken from the Rodents by the usual techniques. This phenomenon could perhaps be explained by the larger size of gametocytes O and I and their retention in the capillaries of the host. 5--The strong infectivity of gametocytes O and I is confirmed by the fact that no infection develops in the Mosquitoes when no such gametocytes are present in the ingested blood. 6--The ageeing of gametocytes appears to be very rapid for gametocytes arising from exo-erythrocytic schizontes reach stage II, 29 hours and stage III, 35 hours, after the rupture of the very first schizonts.