Sensitivity of Plasmodium falciparum to chloroquine in Busia District, Kenya

Human malaria in immunocompromised mice: new in vivo model for chemotherapy studies

We have recently designed a new Plasmodium falciparum mouse model and documented its potential for the study of immune effector mechanisms. In order to determine its value for drug studies, we evaluated its response to existing antimalarial drugs compared to that observed in humans. Immunocompromised BXN (bg/bg xid/xid nu/nu) mice were infected with either the sensitive NF54 strain or the multiresistant T24 strain and then treated with chloroquine, quinine, mefloquine, or dihydroartemisinin. A parallelism was observed between previously reported human responses and P. falciparum-parasitized human red blood cell (huRBC)--BXN mouse responses to classical antimalarial drugs, measured in terms of speed of decrease in parasitemia and of morphological alterations of the parasites. Mice infected with the sensitive strain were successfully cured after treatment with either chloroquine or mefloquine. In contrast, mice infected with the multiresistant strain failed to be cured by chloroquine or quinine but thereafter responded to dihydroartemisinin treatment. The speed of parasite clearance and the morphological alterations induced differed for each drug and matched previously reported observations, hence stressing the relevance of the model. These data thus suggest that P. falciparum-huRBC-BXN mice can provide a valuable in vivo system and should be included in the short list of animals that can be used for the evaluation of P. falciparum responses to drugs.

Using evidence to change antimalarial drug policy in Kenya

Chloroquine resistance was first detected in Kenya in 1978 and escalated during the 1980s. Chloroquine remained the treatment of choice for uncomplicated malaria infections until revised guidelines were launched in 1998 despite a plethora of scientific evidence on failure. This review analyses the range and quality of the evidence base that was used to change the drug policy in Kenya from chloroquine to SP and examines the process of consensus building and decision making. Our review illustrates the difficulties in translating sensitivity data with gross geographical, temporal and methodological variations into national treatment policy. The process was complicated by limited options, unknown adverse effects of replacement therapies, cost, as well as limited guidance on factors pertinent to changing the drug policy for malaria. Although > 50% of the studies showed parasitological failures by 1995, there was a general lack of consensus on the principles for assessing drug failures, the inclusion criteria for the study subjects and the relative benefits of parasitological and clinical assessments. A change in international recommendations for assessment of drug efficacy in 1996 from parasitological to clinical response further perplexed the decisions. There is an urgent need for international standards and evidence-based guidelines to provide a framework to assist the process by which decision-makers in malaria-endemic countries can make rational choices for antimalarial drug policy change.

Response of falciparum malaria in vivo to a standard regimen of chloroquine in Kisumu District, Western Kenya

The sensitivity of Plasmodium falciparum to chloroquine was studied in 140 children in two locations in Western Kenya. The standard WHO in vivo field test was used and chloroquine phosphate 25 mg base/kg administered in divided doses over three days. In one area 13.2% of cases had recrudescent parasitaemias, while in the other area 8.2% of infections were resistant, with 3.5% having an RII pattern. The remaining isolates were sensitive to chloroquine. Further in vivo and in vitro tests in the region are needed to document the extent and level of resistance.

The chemotherapy of rodent malaria XXXV. Further studies on the retardation of drug resistance by the use of a triple combination of mefloquine, pyrimethamine and sulfadoxine in mice infected with P. berghei and 'P. berghei NS'

In the face of an increasing prevalence of Plasmodium falciparum resistant to chloroquine and to pyrimethamine-sulphonamide or -sulphone mixtures, the need for a new, effective blood schizontocide for treatment of acute malaria is urgent. The only such compound that is almost ready for release is mefloquine (M) but there is already a danger that parasites may become resistant to this compound if it is used extensively alone. Earlier studies using a rodent model indicated that mefloquine could be 'protected' by administering it with a pyrimethamine-sulfadoxine (PS) mixture, but the experimental technique used was open to criticism. The present experiments, using a relapse technique to develop drug resistance, more closely parallel the way antimalarials are likely to be deployed in human communities. They confirm that the development of resistance to the individual components in the P. berghei N line is delayed by the triple combination, and more so in the slightly chloroquine-resistant 'P. berghei NS' line. The combination did not prevent the development of resistance in a line initially resistant to PS, but the level reached was much less than those seen when P. berghei N or 'P. berghei NS' were exposed to MPS or to M alone. It was concluded that the use of a triple combination of M, P and S against P. falciparum would be of value in 'protecting' these compounds, and thus gain time while new agents against malaria are being developed.