Falciparum malaria resistant to chloroquine and fansidar: implications for prophylaxis

Direct evidence that asparagine at position 108 of the Plasmodium falciparum dihydrofolate reductase is involved in resistance to antifolate drugs in Tanzania

A nested polymerase chain reaction was used to amplify a fragment of the gene for dihydrofolate reductase of Plasmodium falciparum containing codon 108, where a point mutation, causing a serine to asparagine change, occurs in pyrimethamine resistant parasites. The presence of the mutation was detected by restriction enzyme digestion. Parasites in blood samples collected from asymptomatic children before, and 3 weeks after, treatment with pyrimethamine-sulfadoxine or chlorproguanil-dapsone were analysed. Parasites in the samples taken at 3 weeks carried only the asparagine mutant.

Effect of chloroquine on human lymphocyte proliferation

The effect of chloroquine on human blood mononuclear cells was studied. High concentrations of chloroquine in vitro profoundly suppressed the proliferation of mitogen- and antigen-stimulated cells, as indicated by decreased 14C-thymidine incorporation. Lower concentrations of chloroquine increased the response to pokeweed mitogen. The response to concanavalin A and to various antigens was suppressed, especially the response to large particulate antigens. Oral intake of 300 mg of chloroquine base/week did not affect the lymphocyte proliferative responses. 600 mg of base/week decreased the response to large particulate antigens; the response to small antigens was not affected. The mode of action of chloroquine and the possible consequences of the findings for dosage of chloroquine when used for malaria prophylaxis is discussed.