Declining trend of <i>Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps)</i> mutant alleles after the withdrawal of Sulfadoxine-Pyrimethamine in North Western Ethiopia

Antimalarial drug resistance is one of the major challenges in global efforts of malaria control and elimination. In 1998, chloroquine was abandoned and replaced with sulfadoxine/pyrimethamine, which in turn was replaced with artemether/lumefantrine for the treatment of uncomplicated falciparum malaria in 2004. Sulfadoxine/pyrimethamine resistance is associated with mutations in dihydrofolate reductase (Pfdhfr) and dihydropteroate synthase (Pfdhps) genes. The prevalence of mutation in Pfdhfr and Pfdhps genes were evaluated and compared for a total of 159 isolates collected in two different time points, 2005 and 2007/08, from Pawe hospital, in North Western Ethiopia. The frequency of triple Pfdhfr mutation decreased significantly from 50.8% (32/63) to 15.9% (10/63) (P<0.001), while Pfdhps double mutation remained high and changed only marginally from 69.2% (45/65) to 55.4% (40/65) (P = 0.08). The combined Pfdhfr/Pfdhps quintuple mutation, which is strongly associated with sulfadoxine/pyrimethamine resistance, was significantly decreased from 40.7% (24/59) to 13.6% (8/59) (P<0.0001). On the whole, significant decline in mutant alleles and re-emergence of wild type alleles were observed. The change in the frequency is explained by the reduction of residual drug-resistant parasites caused by the strong drug pressure imposed when sulfadoxine/pyrimethamine was the first-line drug, followed by lower fitness of these resistant parasites in the absence of drug pressure. Despite the decrease in the frequency of mutant alleles, higher percentages of mutation remain prevalent in the study area in 2007/08 in both Pfdhfr and Pfdhps genes. Therefore, further multi-centered studies in different parts of the country will be required to assess the re-emergence of sulfadoxine/pyrimethamine sensitive parasites and to monitor and prevent the establishment of multi drug resistant parasites in this region.抗疟药物耐药性是全球疟疾防控与消除工作面临的核心挑战之一。1998年，氯喹（chloroquine）被停用，改用磺胺多辛/乙胺嘧啶（sulfadoxine/pyrimethamine）取而代之；2004年，后者又被青蒿琥酯/阿莫地喹（artemether/lumefantrine）替代，用于治疗无并发症恶性疟（uncomplicated falciparum malaria）。 磺胺多辛/乙胺嘧啶耐药性与恶性疟原虫二氢叶酸还原酶（dihydrofolate reductase, Pfdhfr）基因及恶性疟原虫二氢蝶酸合酶（dihydropteroate synthase, Pfdhps）基因突变密切相关。本研究对埃塞俄比亚西北部帕韦医院在2005年与2007/2008年两个时间点采集的共159株疟原虫分离株，开展了Pfdhfr与Pfdhps基因突变频率的检测与对比分析。 结果显示，三重Pfdhfr基因突变频率从50.8%（32/63）显著下降至15.9%（10/63）（P<0.001）；而Pfdhps双重基因突变率始终维持在较高水平，仅从69.2%（45/65）小幅波动至55.4%（40/65）（P=0.08）。与磺胺多辛/乙胺嘧啶耐药性强相关的Pfdhfr/Pfdhps五重联合基因突变率，从40.7%（24/59）显著下降至13.6%（8/59）（P<0.0001）。 整体而言，本研究观察到突变等位基因频率显著下降，野生型等位基因重现。该频率变化可归因于两点：其一，当磺胺多辛/乙胺嘧啶作为一线治疗药物时，强药物压力导致的残留耐药寄生虫种群减少；其二，此类耐药寄生虫在无药物压力环境下的适应度降低。 尽管突变等位基因频率有所下降，但2007/2008年时，该研究区域内Pfdhfr与Pfdhps基因的突变率仍处于较高水平。因此，仍需在埃塞俄比亚全国不同地区开展多中心研究，以评估磺胺多辛/乙胺嘧啶敏感性寄生虫的重现情况，并监测与预防多重耐药寄生虫在该区域的定植与扩散。