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Antimicrobial Agents and Chemotherapy, April 2003, p. 1347-1354, Vol. 47, No. 4
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.4.1347-1354.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Molecular Determination of Point Mutation Haplotypes in the Dihydrofolate Reductase and Dihydropteroate Synthase of Plasmodium falciparum in Three Districts of Northern Tanzania

Richard J. Pearce,1* Chris Drakeley,1,2 Daniel Chandramohan,1 Frank Mosha,2,3 and Cally Roper1

Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, United Kingdom,1 Kilimanjaro Christian Medical Centre and,3 The Joint Malaria Programme (JMP) Moshi, Tanzania2

Received 24 September 2002/ Returned for modification 12 November 2002/ Accepted 28 January 2003

The antimalarial combination of sulfadoxine and pyrimethamine (SP) was introduced as first-line treatment for uncomplicated malaria in Tanzania during 2001 following 18 years of second-line use. The genetic determinants of in vitro resistance to the two drugs individually are shown to be point mutations at seven sites in the dihydrofolate reductase gene (dhfr) conferring resistance to pyrimethamine and five sites in the dihydropteroate synthase (dhps) gene conferring resistance to sulfadoxine. Different combinations of mutations within each gene confer differing degrees of insensitivity, but information about the frequency with which allelic haplotypes occur has been lacking because of the complicating effects of multiple infection. Here we used a novel high-throughput sequence-specific oligonucleotide probe-based approach to examine the present resistance status of three Plasmodium falciparum populations in northern Tanzania. By using surveys of asymptomatic infections and screening for the presence of all known point mutations in dhfr and dhps genes, we showed that just five dhfr and three dhps allelic haplotypes are present. High frequencies of both triple-mutant dhfr and double-mutant dhps mutant alleles were found in addition to significant interregional heterogeneity in allele frequency. In vivo studies have shown that the cooccurrence of three dhfr mutations and two dhps mutations in an infection prior to treatment is statistically predictive of treatment failure. We have combined data for both loci to determine the frequency of two-locus genotypes. The triple-dhfr/double-dhps genotype is present in all three regions with frequencies ranging between 30 and 63%, indicating that treatment failure rates are likely to be high.


* Corresponding author. Mailing address: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St., London WC1E 7HT, United Kingdom. Phone: (44) 207 927 2416. Fax: (44) 207 636 8739. E-mail: Richard.Pearce{at}lshtm.ac.uk.


Antimicrobial Agents and Chemotherapy, April 2003, p. 1347-1354, Vol. 47, No. 4
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.4.1347-1354.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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