Plasmodium berghei: Adaptation of a mouse-adapted strain to the Mongolian jird (Meriones unguiculatus); infectivity and immunogenicity

A strain of Plasmodium berghei (K 173) was initially found to be almost noninfective but highly immunogenic for the Mongolian jird (Meriones unguiculatus. The parasite was adapted to this host through serial passage of infected blood. The adapted parasite is 97% lethal to jirds. During adaptation, antigenic changes or shifts in the antigenic profile were found to have occurred, as shown by differences in precipitins raised in rabbits by the original and the adapted strain, as well as by an increased preparent period indicative of an 100-fold loss of infectivity for the mouse after adaptation. Immunogenicity was found to depend upon the continued survival of some (noninfective) parasites in the host, and appears to be determined by antigens different from those responsible for infectivity. Vaccination with nonviable antigens led to the production of some protective antibody, but also to blocking antibody and the retardation of the development of immunity.