Molecular Monitoring of Plasmodium falciparum Resistance to Sulfadoxine-pyrimethamine in Western Kenya, 14 Years after its Withdrawal

Abstract

Background: The application of chloroquine (CQ) as an antimalarial drug for over half a century and subsequent development of CQ-resistant Plasmodium strains has led to its withdrawal and replacement with sulphadoxine-pyrimethamine (SP). In 2004, SP was replaced with artemisininbased combination therapy (ACT) as a first-line against uncomplicated malaria in Kenya with SP being recommended for intermittent preventive in pregnancy (IPTp). Several mutations of Plasmodium falciparum have been implicated in SP resistance but it is unclear if the prevalence of these mutations is decreasing or increasing after it was restricted to expectant mothers. This study was design to assess the current status pfdhfr and pfdhps gene mutation which encodes enzymes targeting SP. Method: Blood from a finger prick was collected onto a filter paper from P. falciparum positive children attending health facility in Chulaimbo between May and November 2015. Using chelex-100 extraction DNA, genotyping was done for mutations on codon 51, 59 and 108 of pfdhr and 437 and 540 of pfdhps genes using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technology. Results: All the 76 P. falciparum isolates were successfully genotyped for the detection of Pfdhfr and Pfdhps mutations associated with SP resistance. The P. falciparum isolates were found to carry the mutant type N51I with a prevalence of 94% while C59R and S108N had 92% each. The prevalence of mutation at Pfdhps codons A437G and K540E stood at 94% and 91% respectively. Conclusion: The present study observed that there is no statistical significant on codon 51I and 437G (χ2 =3.3099 df=1 p>0.05) change in the proportion of resistant genotypes. However, there was a statistical significant on codon 59R and 108N (χ2 =4.338 df=1 p<0.05) and 540E (χ2 =5.391 df=1 p<0.05) indicating a slow but steady decreased resistance despite its withdrawal. In addition, the evidence of quintuple mutations in the study population is threatening the future of SP especially in intermittent preventive treatment prophylaxis (IPTp) programs and also future combination with another antimalarial drug. These findings highlight the need for continual monitoring of parasites genotypes as indicators of therapeutic efficacy of antimalarial. Keywords: Sulfadoxine-pyrimethamine; Drug resistance; Plasmodium falciparum; pfdhfr; pfdhps