Plasmodium falciparum mutant haplotype infection during pregnancy associated with reduced birthweight, Tanzania

Abstract

Intermittent preventive treatment during pregnancy with sulfadoxine-pyrimethamine (IPTp-SP) is a key strategy in the control of pregnancy-associated malaria. However, this strategy is compromised by widespread drug resistance from single-nucleotide polymorphisms in the Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthetase genes. During September 2008-October 2010, we monitored a cohort of 924 pregnant women in an area of Tanzania with declining malaria transmission. P. falciparum parasites were genotyped, and the effect of infecting haplotypes on birthweight was assessed. Of the genotyped parasites, 9.3%, 46.3%, and 44.4% had quadruple or less, quintuple, and sextuple mutated haplotypes, respectively. Mutant haplotypes were unrelated to SP doses. Compared with infections with the less-mutated haplotypes, infections with the sextuple haplotype mutation were associated with lower (359 g) birthweights. Continued use of the suboptimal IPTp-SP regimen should be reevaluated, and alternative strategies (e.g., intermittent screening and treatment or intermittent treatment with safe and effective alternative drugs) should be evaluated.

Keywords: Plasmodium falciparum; Tanzania; dihydrofolate reductase; dihydropteroate synthetase; drug resistance; haplotype; intermittent preventive treatment; low birth weight; malaria; mutations; parasites; polymorphisms; pregnancy; sextuple; sulfadoxine-pyrimethamine.

Figure 1

Pfdhfr/Pfdhps haplotyping results for Plasmodium falciparum parasite isolates from 54 parasite isolates in 49 pregnant women, Korogwe District, Tanga Region, Tanzania, September 2008–October 2010. A) Proportion of single nucleotide polymorphisms (SNPs) conferring sulfadoxine–pyrimethamine resistance on the P. falciparum dihydrofolate reductase gene (Pfdhfr) at codons C50, N51I, C59R, S108N, and L164I, resulting in allelic haplotypes CNCSI (wild-type), CICNI (double Pfdhfr mutant), CNRNI (double Pfdhfr mutant), and CIRNI (triple Pfdhfr mutant). B) Proportion of SNPs conferring sulfadoxine–pyrimethamine resistance on the P. falciparum dihydropteroate synthetase (Pfdhps) gene at codons S436A, A437G, K540E, A613S/T, and A581G with allelic haplotypes AKAA (wild-type), AGEAA (double Pfdhps mutant), SGEAA (double Pfdhps mutant), and SGEGA (triple Pfdhps mutant). C) Proportions of Pfdhfr/Pfdhps quadruple or less, quintuple, and sextuple mutant haplotypes from the cohort of pregnant women. The derivations of the allelic haplotypes were based on a combination of 2 or 3 Pfdhfr SNPs with 2 or 3 Pfdhps SNPs forming quadruple (4 SNPs), quintuple (5 SNPs), and sextuple (6 SNPs) haplotypes. Quadruple haplotype or less included 4 SNPs (quadruple) and triple Pfdhfr (CIRNI, n = 1) or double dhps (SGEAA, n = 1) with wild-type dhfr (CNCSI, n = 1) or wild-type dhps (AKAA, n = 1). Less than 4 haplotypes had 1 triple or double mutation in 1 gene combined with a wild-type mutation in the other gene.

Figure 2

Proportion of mutant Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthetase haplotypes among pregnant women, Korogwe District, Tanga Region, Tanzania, September 2008–October 2010. Proportions are shown by gestational age; partial weeks are indicated by the number of days. Numbers above and below data points are the number of mutant haplotypes; total numbers (n) are shown below the graph.