Serial studies on the evolution of drug resistance in malaria in an area of east Africa: findings from 1979 up to 1986.

Observations, previously reported for 1979-82, have been continued up to 1986 on the development of drug resistance in P. falciparum in the North Mara area of Tanzania, where a chloroquine chemosuppression campaign was attempted from 1977 to 1982. The WHO micro in-vitro test for chloroquine and other drugs was used. Because of the large number of tests done, each test was characterized by the mean minimum inhibitory concentrations (MIC) of drug needed to prevent schizont development instead of counting the numbers of schizonts. The MIC for chloroquine has risen progressively each year but changes in the findings of in-vivo tests were less dramatic possibly due to the effects of immunity. Resistance to amodiaquine has followed that to chloroquine at a lower level, and in the last years the MIC for quinine has risen. Sporadic resistance to mefloquine was found and, by in-vivo test, to sulphadoxine-pyrimethamine. Possible factors in the evolution of drug resistance are discussed together with implications for the future.