Trends in drug resistance codons in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase genes in Kenyan parasites from 2008 to 2012

Abstract

BackgroundSulphadoxine-pyrimethamine (SP), an antifolate, was replaced by artemether-lumefantrine as the first-line malaria drug treatment in Kenya in 2004 due to the wide spread of resistance. However, SP still remains the recommended drug for intermittent preventive treatment in pregnant women and infants (IPTP/I) owing to its safety profile. This study assessed the prevalence of mutations in dihydrofolate reductase (Pfdhfr) and dihydropteroate synthase (Pfdhps) genes associated with SP resistance in samples collected in Kenya between 2008 and 2012.MethodsField isolates collected from Kisumu, Kisii, Kericho and Malindi district hospitals were assessed for genetic polymorphism at various loci within Pfdhfr and Pfdhps genes by sequencing.ResultsAmong the Pfdhfr mutations, codons N51I, C59R, S108N showed highest prevalence in all the field sites at 95.5%, 84.1% and 98.6% respectively. Pfdhfr S108N prevalence was highest in Kisii at 100%. A temporal trend analysis showed steady prevalence of mutations over time except for codon Pfdhps 581 which showed an increase in mixed genotypes. Triple Pfdhfr N51I/C59R/S108N and double Pfdhps A437G/ K540E had high prevalence rates of 86.6% and 87.9% respectively. The Pfdhfr/Pfdhps quintuple, N51I/C59R/S108N/A437G/K540E mutant which has been shown to be the most clinically relevant marker for SP resistance was observed in 75.7% of the samples.ConclusionSP resistance is still persistently high in western Kenya, which is likely due to fixation of key mutations in the Pfdhfr and Pfdhps genes as well as drug pressure from other antifolate drugs being used for the treatment of malaria and other infections. In addition, there is emergence and increasing prevalence of new mutations in Kenyan parasite population. Since SP is used for IPTP/I, molecular surveillance and in vitro susceptibility assays must be sustained to provide information on the emergence and spread of SP resistance.

Increasing Prevalence of a Novel Triple-Mutant Dihydropteroate Synthase Genotype in Plasmodium falciparum in Western Kenya

“…Similarly, at least five SNPs in Pfdhps are reported to be involved in resistance to sulfadoxine, including S436A/F, A437G, K540E, A581G, and A613S/T. In Africa, the most commonly observed genotype conferring pyrimethamine resistance is the Pfdhfr triple-mutant genotype C 50 I 51 R 59 N 108 I 164 (reviewed in references 1 and 5), which was recently found at frequencies of as high as 80% in East Africa (6). The addition of a fourth mutation, I164L, has been shown to lead to a highly resistant phenotype (7,8), but this I164L mutation is observed only at a low prevalence in western Kenya (6,9,10).…”

“…In Africa, the most commonly observed genotype conferring pyrimethamine resistance is the Pfdhfr triple-mutant genotype C 50 I 51 R 59 N 108 I 164 (reviewed in references 1 and 5), which was recently found at frequencies of as high as 80% in East Africa (6). The addition of a fourth mutation, I164L, has been shown to lead to a highly resistant phenotype (7,8), but this I164L mutation is observed only at a low prevalence in western Kenya (6,9,10). In Pfdhps, two different patterns of resistance have been reported in Africa: the 437G and 540E mutations are commonly reported in East Africa, while in West and Central Africa, the 436A and 437G mutations are common (11)(12)(13).…”

“…Recent studies in East Africa have reported the emergence of triple Pfdhps mutants involving the addition of an SNP at codon 581 or 613 to the double-mutant A437G/K540E genotype (8,(14)(15)(16)(17). These additional Pfdhps mutations, A581G or A613S/T, have been reported to be present at a low prevalence in P. falciparum isolates collected from western Kenya (6,10). However, a novel mutation at codon 436 (S436H) was found in western Kenya (6,10) and, to the best of our knowledge, has not been reported elsewhere.…”

Clinical efficacy of artemisinin-lumefantrine and status of antifolate drug resistance markers in western Kenya

“…Though the southern parts of Tanzania have lower levels of SP resistance, the northwestern part bordering Kenya and Uganda has higher levels of SP resistance [60]. Similarly, an increase of Pfdhps 540E from 33.1% in 1996 to 99.2% in 2009 was reported in Kenya [57].…”

“…This may suggest that the Pfdhfr allele has evolved independently due to the drug pressure in geographically different regions of the world. A study in western Kenya from pregnant women between 2008 and 2009 was found to harbor more than 90% Pfdhps double mutants and more than 80% of quintuple mutations [57]. In Mozambique, SP resistance quintuple mutation was reported to be above 75% in 2008 while triple mutation had reached 100% fixation [14].…”