Decreased sensitivity to chloroquine and quinine of some Plasmodium falciparum strains from Senegal in September 1984.

The in vitro sensitivity of 135 Plasmodium falciparum isolates collected in the areas of Thies and Kaolack, Senegal, were studied in September 1984, by means of the 48 hr microtest with 3H-hypoxanthine incorporation. Results are available in 110 of 135 cases studied (81%). The isolates collected around Kaolack were found on average less sensitive to chloroquine than those from Thies (mean EC50 28 and 17 nmol/l of medium, respectively, P less than 0.05) and in 1 isolate a high degree of resistance was found (EC50 178 nmol/l). Some of those isolates also were studied using the WHO standard microtest and similar results were recorded. With both assays probit regression lines show EC99 in Kaolack greater than 114 nmol/l. These data suggest that in 1984 chloroquine resistance was possibly emerging in the extreme west of Africa. Sensitivity to quinine could be evaluated in 15 of 24 isolates tested. One of them, originating from Thies, was highly resistant to this drug (EC50 760 nmol/l) and 2 additional isolates with EC50s of 370 and 274 nmol have decreased sensitivity. These results suggest that quinine, as well as chloroquine, sensitivity should be monitored in the African region.