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Sulfadoxine-pyrimethamine (SP), the current first line antimalarial drug in Tanzania, is compromised by
evolution and spread of mutations in the parasite's dhfr and dhps genes. In the present study we established the baseline
frequencies of Plasmodium falciparum dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) mutant
genotypes and their potential for predicting the in vivo efficacy of SP in Mlandizi, Tanzania. The efficacy of SP treatment
was by following 116 children with uncomplicated falciparum malaria for 14 days after treatment. Infected blood samples
were collected on filter paper at days 0, 3, 7 and 14. Parasite genomic DNA was extracted and point mutations at positions
51, 59, 108 and 164 of the dhfr gene and at 581, 540 and 437 of the dhps gene were analysed by nested Polymerase Chain
Reaction/ Restriction Fragment Length Polymorphism. Out of 116 children enrolled, 98 (86%) of eligible children
demonstrated an adequate clinical response by day 14. There were 7.3 % early and 6.7% late therapeutic failures. At day
0, only 8.0% (4/50) the parasites showed no mutation at the dhfr locus; for dhps this was 73%. Triple mutant dhfr alleles
(Ile 51, Arg 59, Asn 108) occurred in 47%, double mutant dhps (Gly 437, Glu 540) alleles in 7.9%. No mutation was
detected at codon 164 of the dhfr gene. The presence of triple dhfr mutant alleles was related to clinical failure, but did not
show significant association (Fisher exact test, P=0.166, OR 2.15 0.77<OR>6.20). The higher rates of mutation on the dhfr
do not spell a bright future for SP treatment in Tanzania. It is rational to think of an alternative first line antimalarial drug,
while retaining SP for malaria intermittent treatment in pregnancy. |
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