At a temperature of 26°C. oocysts of P. berghei in A. quadrimaculatus fed on infected white mice contained sporozoites by the 6th day, with a peak number of oocysts containing sporozoites on the 9th day. The decrease in proportion of sporozoite-bearing oocysts after this time indicated that migration of the sporozoites to the salivary glands would normally take place at this time. However, infected glands were never found. Development of P. berghei to the oocyst stage was also obtained in two additional species of Anopheles not previously reported. Two species of culicine mosquitoes showed no evidence of infection with P. berghei.
Attempts to obtain sporozoite-induced infections in mice, rats, and hamsters by intravenous and intraperitoneal inoculation of stomachs with large numbers of mature oocysts, salivary glands or entire mosquitoes were unsuccessful.
The rodent host used as a source of the infecting blood meal appeared to be an important factor in the percentage of mosquitoes infected and oocyst development. A higher percentage of A. quadrimaculatus became infected and the number of oocysts per infected mosquito stomach was greater when mice were used as the source of the infecting meal than was the case when the same species of mosquito was fed on rats or hamsters. In addition, sporozoites developed more readily in mosquitoes whose infective blood source was mice.
The time of feeding with respect to the parasitemia peak in the rodent host had a most pronounced effect on the percentage of mosquitoes infected. Rodents in the early stages of the disease were more infective for mosquitoes than were rodents at or past the parasitemia peak.
The course of the Kasapa strain of P. berghei was determined for a small series of mice inoculated intravenously and hamsters inoculated intraperitoneally with a counted number of parasites. With 3 different sizes of inoculum the patency of the infection in white mice was delayed with the smallest dose, although the average day of death was about the same for the three groups. A ten-fold difference in inoculum seemed to exert little influence on the duration and course of the parasitemia in intraperitoneally inoculated hamsters.