Cyclical transmissions of Plasmodium berghei by the bite of experimentally infected Anopheles quadrimaculatus and A. stephensi and by inoculation of sporozoites were carried out in 179 laboratory-bred animals. No differences were observed between the duration of the prepatent periods in sporozite-induced infections in Thamnomys surdaster, the natural mammalian host, and in experimental hosts, the white mouse, the golden hamster and the young albino rat.
The route of sporozoite inoculation did not alter the duration of the prepatent period. Parasitemia was observed as early as 65 hours after sporozoite inoculation. Seventy-seven percent of animals showed prepatent periods of 4 to 6 days, but incubation periods of 7, 8, 9, and 10 days were also observed.
The number of sporozoites inoculated did not alter the prepatent period. The duration of prepatency was similar (6 days) following intracardial inoculation of 360 and 72,000 sporozoites.
A negative non-infective phase of the blood during prepatency after sporozoite inoculation was demonstrated. This period lasted from 2 hours after sporozoite inoculation to 51 hours.
Pre-erythrocytic tissue schizonts of P. berghei were discovered in stained liver sections of a young hamster, two tree rats (Thamnomys), and one young albino rat inoculated with massive doses of sporozoites and killed 51–72 hours after initial sporozoite inoculation. The morphology of the pre-erythrocytic tissue schizonts of P. berghei in the parenchyma cells of the liver is described and their growth and pattern of development compared with other known mammalian tissue forms.