Plasmodium falciparum Mutant Haplotype Infection during Pregnancy Associated with Reduced Birthweight, Tanzania - Vol. 19 No. 9 - September 2013 - Emerging Infectious Disease journal - CDC
Table of Contents
Volume 19, Number 9–September 2013
Volume 19, Number 9—September 2013
Plasmodium falciparum Mutant Haplotype Infection during Pregnancy Associated with Reduced Birthweight, Tanzania
Pregnancy-associated malaria is a leading cause of maternal anemia and low birthweight (1). Measures to prevent pregnancy-associated malaria include insecticide-treated nets, treatment with effective antimalarial drugs, and administration of intermittent preventive treatment during pregnancy with sulfadoxine–pyrimethamine (IPTp-SP) (2). IPTp-SP is given at least twice during pregnancy, with doses 1 month apart (3,4). Studies have shown that IPTp-SP reduces the incidence of anemia, clinical malaria, low birthweight, and parasite prevalence at delivery (3,5–9).
AbstractIntermittent 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.
SP acts by inhibiting the Plasmodium falciparum dihydropteroate synthetase and dihydrofolate reductase enzymes, respectively (10,11). However, resistance to the combined drug (SP) is widespread among the P. falciparum population in sub-Saharan Africa; this resistance is caused by accumulation of point mutations in the P. falciparum dihydropteroate synthetase (Pfdhfr) and dihydrofolate reductase (Pfdhps) genes (12,13). An increased number of point mutations in these genes is associated with augmented resistance to SP in vivo (14). There is sufficient evidence to support that the triple Pfdhfr mutation asparagine 51 to isoleucine (N51I), cysteine 59 to arginine (C59R), and serine 108 to asparagine (S108N) in combination with double Pfdhps mutant alanine 437 to glycine (A437G) and lysine 540 to glutamic acid (K540E)—forming quintuple mutant haplotypes—confer a high risk for treatment failure in malaria-infected children and nonpregnant adults who receive SP treatment (14). In addition, recent reports have shown that an increase in Pfdhps mutations at alanine 581 to glycine (A581G), further escalating the risk for even higher levels of resistance (15).
Because P. falciparum parasite resistance to SP is high, most likely because of the high prevalence of quintuple mutant haplotypes, use of the drug to treat uncomplicated malaria has been abandoned in many parts of eastern Africa. In Tanzania, SP was replaced in 2006 by artemether-lumefantrine for the management of uncomplicated malaria (4). The high prevalence (> 50%) of the K540E mutation, which is found almost exclusively as the quintuple mutant haplotype, has also resulted in poor SP efficacy when used as intermittent preventive treatment in infants (16). However, other studies have indicated that IPTp-SP is still efficacious in some areas with high resistance (17). Nonetheless, with increased P. falciparum resistance, the usefulness of IPTp-SP might be compromised (18–20).
It has not been known whether there is an association between P. falciparum sextuple mutant haplotypes and poor pregnancy outcome. To determine if there is a relationship, we conducted a prospective cohort study in northeastern Tanzania in an area with declining malaria transmission (21). The study received ethical approval from the Tanzania Medical Research Coordinating Committee (reference no. NIMR/HQ/R.8a/Vol. IX/688). All procedures were conducted in accordance with the Declaration of Helsinki and Good Clinical and Laboratory Practices. All participants gave written informed consent.