[Plasmodium yoeli 265 BY--new possibilities in the study of the resting stages of the malarial parasites].

When Swiss mice were experimentally infected with P. yoelii yoelii 264 BY sporozoites through bites of the mosquito Anopheles stephensi, there were no blood parasites in most (85%) animals after a short (on day 4-5) incubation period. The hepatic parenchymal cells from the animals without primary infection manifestation (following 2 months of the infection) or with the disease self-arrested (on day 26 of postinfection) were the first to display 5-11-microunits mononuclear parasites that are likely to be similar to the hypnozoites of some malaria parasite strains in man and primates. This suggests that rodent malaria parasites, as P. vivax, might cause infection with prolonged incubation and true relapses previously unknown for these parasites. Therefore, P. yoelii is a promising accessible model for studying the persistence phenomenon of malarial parasites at the tissue level.