Two mutations in dihydrofolate reductase combined with one in the dihydropteroate synthase gene predict sulphadoxine-pyrimethamine parasitological failure in Ugandan children with uncomplicated falciparum malaria.

The point mutations in the Plasmodium falciparum dihydrofolate reductase (dhfr) and the dihydropteroate synthase (dhps) genes that are linked to sulphadoxine-pyrimethamine (SP) resistance in vitro have been well characterised. To determine whether a few of these mutations could predict SP treatment failure in vivo, two mutations (Asn-108 and Arg-59) in the dhfr gene and one (Glu-540) in the dhps gene were analysed according to the risk of SP parasitological failure (RI-RIII) at day 28 in pre-treatment isolates in 79 Ugandan children aged 6-59 (mean = 18.4, S.D. = 8.8) months with uncomplicated falciparum malaria. Neither the dhfr-108 (P = 0.3) nor the dhps-540 (P = 0.6) or dhfr-108 + dhps-540 (P = 0.04) mutations were significantly associated with SP parasitological failure. However, the dhfr-108 + dhfr-59 (P = 0.04), the dhfr-59 + dhps-540 (P = 0.04) and the dhfr-108 + dhfr-59 + dhps-540 (P = 0.02) mutations significantly increased the risk for SP parasitological failure. Our findings confirm an earlier report that the dhfr-59 and the dhps-540 mutations could be useful genetic markers for rapid screening of populations at high risk of SP resistance.

Efficacy of sulphadoxine-pyrimethamine alone or combined with amodiaquine or chloroquine for the treatment of uncomplicated falciparum malaria in Ugandan children.

The rapid development of falciparum resistance to sulphadoxine-pyrimethamine (SP) in East and Central Africa has raised concerns as to the efficacy of combining it with another drug. In 2002, we assessed the efficacy of SP alone and combined with amodiaquine (AQ/SP) or chloroquine (CQ/SP) in Ugandan children with uncomplicated falciparum malaria. At day 14, adequate clinical response was 100% (84/84) for AQ/SP, 93% (92/101) for CQ/SP and 91% (73/80) for SP. At day 28, parasitological failure (RI-RIII) occurred in 16% (13/80) of children treated with AQ/SP, in 48% (48/100) of those treated with CQ/SP and in 61% (48/79) of those treated with SP alone. Compared with the AQ/SP arm, the odds for parasitological failure at day 28 were five times higher (95% CI, 2-10) in the CQ/SP group and sevenfold higher (95% CI, 3-17) in that of SP alone. CQ/SP does not offer any significant added benefit over SP alone while AQ/SP is an efficacious low-cost combination. These findings have important policy implications for Uganda and other resource-constrained African countries faced with the problematic choice of a new first-line antimalarial treatment in a context of high CQ resistance.

Intensity of transmission and spread of gene mutations linked to chloroquine and sulphadoxine-pyrimethamine resistance in falciparum malaria.

The number of malaria parasite clones per infection-multiplicity of parasite clones-is affected by the transmission intensity, multiplicity increases with increasing transmission. This affects the frequency of parasites' sexual recombination and, if several mutations in different genes are involved, can break down drug resistant genotypes. Therefore, the effects of malaria transmission intensity on the spread of drug resistance could vary depending on the number of genes involved. Here we show that, compared to low transmission, intermediate-high transmission is associated with a 20-100-fold lower risk for the mutations linked to chloroquine resistance and a 6-17 times higher risk for those linked to sulphadoxine-pyrimethamine resistance. This is consistent with the hypothesis of a multigenic basis for chloroquine resistance and a monogenic basis for that of sulphadoxine-pyrimethamine. Reducing transmission intensity could slow the spread of resistance. However, a reduction below a critical threshold (e.g. when parasite prevalence in children 2-9 years old is around 60-80%) could, paradoxically, accelerate the spread of resistance to chloroquine and possibly to other drug combinations whose basis is multigenic. Our findings have important implications for malaria control because increasing drug resistance has a substantial impact on mortality.