Molecular monitoring of Plasmodium falciparum resistance to sulfadoxine-pyrimethamine in western Kenya, 14 years after its withdrawal

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 artemisinin-based combination therapy (ACT) as a first-line against uncomplicated malaria in Kenya. The sudden surge in ACT resistant against P. falciparum in Cambodia and neighboring countries had become a stumbling block in the management and control of this preventable and curable disease. The resistance associated with P. falciparum is linked to multiple mutations in the parasite’s dihydrofolate reductase and dihydropteroate synthase genes. This study assesses the prevalence of pfdhfr and pfdhps gene mutation which encodes enzymes targeting SP. Method: Briefly, blood taken from a finger prick was collected on 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. The enzymes used to digest the respective codons were Tsp5091, Amxn I, Alu I, Ava II and Fok I respectively. 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 that are likely to become fixed in the study population is threatening the future of SP especially in intermittent preventive treatment prophylaxis (IPTp) programs.