Previous evaluations of the timing of developing stages in the erythrocytic cycle of the simian malaria parasite, Plasmodium cynomolgi, a frequently used model for relapsing malaria in man, have depended on procurement of blood samples at 4- or 6-hourly intervals. This brief report describes the blood cycle as determined from hourly bleedings, thus providing a more discriminating sequence usable for immunochemical or biochemical study of specific stages. The approximate timing of development for five defined stages in the asexual cycle was determined to be 12–14 hours for young trophozoites, 22–24 hours for developing trophozoites, 5–7 hours for mature trophozoites, 5–6 hours for early schizonts, and 3–5 hours for late schizonts. It was also demonstrated that the rate of erythrocytic multiple infection declined in proportion to the maturity of the parasite. Young and developing trophozoites presented the most numerous cases of multiple infection whereas very few schizonts were seen multiply infecting a host cell.
Present address: Scripps Clinic and Research Foundation, La Jolla, California 92037.