Epidemiological significance of repeated infections with homologous and heterologous strains and species of Plasmodium.

During many years of experience with the use of induced malaria for the therapy of neurosyphilis, it has been possible to observe the course of malarial infections in patients with known previous history of infection by the same and different strains and species of Plasmodium. This report presents the effect of prior infection on subsequent infection in regard to immune response of the host, clinical symptoms, parasitaemia, transmissibility and chemotherapeutic measures. These studies have shown that in no case was it impossible to induce additional infections in patients. However, in all homologous-species reinoculations, there were significant modifications of the infections, which were enhanced if both exposures were to the same strain. Variable results (ranging from no apparent effect to a fairly substantial modification) were seen after reinoculation of patients with a heterologous species of Plasmodium.The use of immunofluorescent methods may provide a clearer understanding of the mechanism of partial immunity as it affects reinfection. The relationship of this partial immunity to the epidemiology and chemotherapy of the disease in endemic areas is of importance, in that these infections in semi-immune persons provide a continuing and unapparent source of reinfection of the community.