I. The Characteristics of Untreated Sporozoite-Induced and Trophozoite-Induced Infections

Abstract

This report summarizes the results of a longitudinal study of the characteristics of untreated infections with trophozoites and sporozoites of the M, B, and Ro strains of P. cynomolgi. The pre-initial-peak phases of infections with trophozoites of these strains were remarkably similar. These phases of sporozoite-induced infections were also similar except that infections with the B and Ro strains had a shorter incubation period and reached the initial peak more promptly than infections with the M strain. The post-initial-peak phase of the primary attack in infections with the M strain was significantly shorter than that phase of infections with either the B or Ro strain and was characterized by parasitemias of lesser intensity and fewer secondary peaks. The total duration of infections with trophozoites of either the M or B strain from onset of patency to self-cure was markedly shorter than the duration of infections with sporozoites of these strains. The duration of infections with sporozoites of the B strain was significantly longer than the duration of infections with the M strain. Monkey-to-monkey variations in the features of the post-initial-peak phase of infections, including the frequency of secondary attacks and the total duration of disease, were substantial. Although malaria morbidity was a common feature of primary attacks, the incidence of malaria deaths was low in infections with all three strains.