Variation of incubation time in an in vitro drug susceptibility test of Plasmodium falciparum isolates studied in the Solomon Islands

A study on chloroquine resistance of falciparum malaria was conducted in the Solomon Islands. Both in vitro and clinical tests were performed. In our regular studies of in vitro chloroquine susceptibility tests on Plasmodium falciparum from non-immuners in Japan, the threshold point to differentiate resistant and susceptible isolates was set at a 0. 114 microM chloroquine in the semi-micro culture system, and this point was also applicable in the study of the malaria parasite taken in the highly endemic malarious area with good coincidence with clinical observation. Variation in the incubation time (24-63) to reach the schizont stage of the isolated parasites were noted. It appeared that chloroquine resistant P. falciparum showed traits to reach the schizont stage within a shorter incubation period.