Chloroquine resistant Plasmodium falciparum: effect of rabbit serum and incubation time on the in vitro (microtechnique) prediction of in vivo resistance.

A study of chloroquine resistance of 54 isolates of Plasmodium falciparum is reported. Sixty-four percent of the isolates tested produced schizonts in vitro (micro-technique), whereas the remaining 36 percent did not. The accuracy of the in vitro test to predict in vivo resistance was increased when the primary parasite isolates were cultured in the presence of rabbit serum and when the cultures were allowed to incubate for more than 48 hours. Thirteen isolates of P. falciparum that showed in vitro resistance were confirmed in vivo resistant. Eleven of these cases were identified as R-I and two as R-II. Only one case of in vivo resistance (R-II) was observed among the 19 isolates that failed to produce schizonts in vitro.

Chloroquine and quinine resistant Plasmodium falciparum on the island of Mindoro, Philippines, 1982.

A field study was conducted on the island of Mindoro, Republic of the Philippines in which over 800 persons were screened for malaria and approximately 8% were found positive. The in vitro microtechnique was used to test for sensitivity to chloroquine, amodiaquine, mefloquine and quinine in 20 slide-confirmed P. falciparum cases. Sixteen of these cases were also followed for in vivo chloroquine sensitivity. Four cases showed in vitro resistance to chloroquine; 2 also showed resistance to quinine. All showed in vitro sensitivity to mefloquine and amodiaquine. The results of in vivo test were consistent with either a sensitive (S) or R-1, resistant response to chloroquine. Taken together, the in vitro and in vivo chloroquine tests indicate 4 cases of chloroquine resistance at the R1 level.

A preliminary survey of malaria in Occidental, Mindoro, Philippines.

A survey of malaria in Northwest Mindoro, Occidental, Mindoro, Philippines is reported. Three species of human plasmodia were identified from 600 blood films examined. The overall prevalence of malaria was 7% (2.8% P. falciparum, 4.3% P. vivax, 0.7% P. malariae). The prevalence of malaria was highest (24%) among children 0 to 15 years of age and only 4 cases (12%) were found among persons over the age of 15. Males and females were equally infected. Study sites with the highest slide-positivity rate were located in the foothill regions which corresponded with the observed presence of two malaria vectors, Anopheles minimus flavirostris and An. maculatus. These sites appeared to be adequate for future studies of drug-resistance, although large numbers of suitable candidates would not be expected.