Sensitivity of Plasmodium falciparum isolates to chloroquine in Kisumu and Malindi, Kenya.

The chloroquine sensitivity of Plasmodium falciparum isolates from infected persons living in Kisumu and Malindi, Kenya, was determined in vivo and vitro. There was no evidence of chloroquine resistance in 217 patients with P. faliparum infections who underwent standard W.H.O. 7-day in vivo tests. In 71 extended 35-day in vivo tests parasitemia recurred in 14 patients on days 21, 28, or 35. Parasites isolated from these 14 persons during the following period were tested in vitro. Eight tests were successful and showed the isolates to be chloroquine sensitive in vitro, suggesting that the recurrence of parasitemia resulted from reinfection rather than resistance. Macro in vitro tests were done on an additional 67 infected persons, 11 of whom also had sensitive 7-day in vivo tests. Chloroquine resistance was not demonstrated in vitro. In Malindi 100% of isolates were inhibited by a chloroquine concentration of less than or equal to 0.75 nmol/ml blood and 80% by less than or equal to 0.5 nmol as compared with 69% and 27.3% respectively of those from Kisumu. These data from individuals living in malarious areas of Kenya contrast with continuing reports of proven chloroquine-resistant P. falciparum malaria in non-immune visitors who acquired their infections in Kenya.

Field evaluation in Kenya of a 48-hour in vitro test for Plasmodium falciparum sensitivity to chloroquine.

A 48-hour in vitro test for determining the chloroquine sensitivity of Plasmodium falciparum isolates was evaluated in Kisumu and Malindi, Kenya. P. falciparum isolates from 14 children, aged 5 to 13 years, were studied. In vivo and 48-hour in vitro tests were done on all 14. Successful Rieckmann macro and micro in vitro tests for chloroquine sensitivity were completed in nine isolates each. All 14 infections cleared within 3 days of beginning chloroquine treatment, and none recrudesced during a 7-day (8 patients) or 28-day (6 patients) follow-up period. The three in vitro tests gave comparable results. Although all isolates tested were chloroquine sensitive in vitro, different response patterns were observed. In the 48-hour test, 10 isolates were inhibited at chloroquine concentration less than or equal to 0.03 nmol/ml medium. These isolates were inhibited by less than or equal to 0.5 nmol of chloroquine per ml blood in the Rieckmann macro test and by 2-6 pmol/well in the micro test. The other four isolates had response patterns intermediate between those of previously reported sensitive and resistant strains. Complete inhibition did not occur until chloroquine concentrations of greater than or equal to 0.03 nmol/ml medium in the 48-hour test, greater than or equal to 0.5 nmol/ml blood in the macro test, and 6 pmol/well in the micro test. The results demonstrate that the 48-hour test is a useful addition to existing in vivo and in vitro methods for determining the chloroquine sensitivity of P. falciparum in the field.

Sensitivity of Plasmodium falciparum to chloroquine in Busia District, Kenya.

Individuals infected with Plasmodium falciparum were randomly divided into two groups; one group was treated with a single dose of 10 mg chloroquine base per kg. body-weight and the other with 25 mg base of chloroquine per kg body-weight given over three days, followed by an observation period of seven days. By Day 3 of observation complete parasite clearance had occurred in all the 125 triple dose recipients and 113 of 114 (99.1%) of those who had the single dose. 94.4% of 36 isolates tested in vitro by the macrotechnique were sensitive to drug concentration of 0.75 nmol/ml blood or less. On isolate was relatively less sensitive and required a concentration of chloroquine of 1.50 nmol/ml to inhibit schizont growth. However, the same isolate responded well to 25 mg base of chloroquine. These findings have demonstrated that, at present, isolates of P. falciparum in Busia District are sensitive to the standard dose of 10 mg chloroquine base and there is no reason therefore to resort to alternative antimalaria drugs. These should be reserved for special cases only.

Morbidity in urinary schistosomiasis in relation to the intensity of infection in Kisumu, Kenya.

A study of the morbidity due to schistosomiasis haematobium was undertaken in 121 children ranging in age from 5 to 19 years, from Kanyamedha Primary School, Kisumu. Of this sample 81% of the males and 42% of the females had Schistosoma haematobium. Proteinuria was detected in 23% of the uninfected children; 54% of those with light infection; 80% of those with moderate infection and 94% of those with heavy infection. Similarly, haematuria was detected in 18% of the apparently uninfected individuals, 64% of those lightly infected, and 76% and 94% of those with moderate and heavy infections, respectively. Three of the 20 children given intravenous pyelography had renal and bladder complications, characterized by hydronephrosis, bladder granuloma, bladder calcification and hydroureter.

In vitro response of Plasmodium falciparum to chloroquine in the Nandi district, Kenya.

Thirty-six isolates of Plasmodium falciparum from Nandi district, Kenya, which were tested for their sensitivity to chloroquine using the WHO in vitro macrotechnique, yielded a total of 29 successful tests, one of which showed overt resistance with schizont maturation at chloroquine levels of > 1.5 x 10(-6) mol/l. The majority of isolates showed reduced sensitivity to chloroquine, and the EC(99) was 1.7218 x 10(-6) mol/l. These findings are indicative of widespread in vitro resistance of a low degree which may remain largely unnoticed in immune individuals. However, in nonimmune subjects one may expect also in vivo resistance because the parasites will not be completely cleared after a normally curative dose of chloroquine.