Pearce Richard J, Drakeley Chris, Chandramohan Daniel, Mosha Frank, Roper Cally
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, United Kingdom.
Antimicrob Agents Chemother. 2003 Apr;47(4):1347-54. doi: 10.1128/AAC.47.4.1347-1354.2003.
The antimalarial combination of sulfadoxine and pyrimethamine (SP) was introduced as first-line treatment for uncomplicated malaria in Tanzania during 2001 following 18 years of second-line use. The genetic determinants of in vitro resistance to the two drugs individually are shown to be point mutations at seven sites in the dihydrofolate reductase gene (dhfr) conferring resistance to pyrimethamine and five sites in the dihydropteroate synthase (dhps) gene conferring resistance to sulfadoxine. Different combinations of mutations within each gene confer differing degrees of insensitivity, but information about the frequency with which allelic haplotypes occur has been lacking because of the complicating effects of multiple infection. Here we used a novel high-throughput sequence-specific oligonucleotide probe-based approach to examine the present resistance status of three Plasmodium falciparum populations in northern Tanzania. By using surveys of asymptomatic infections and screening for the presence of all known point mutations in dhfr and dhps genes, we showed that just five dhfr and three dhps allelic haplotypes are present. High frequencies of both triple-mutant dhfr and double-mutant dhps mutant alleles were found in addition to significant interregional heterogeneity in allele frequency. In vivo studies have shown that the cooccurrence of three dhfr mutations and two dhps mutations in an infection prior to treatment is statistically predictive of treatment failure. We have combined data for both loci to determine the frequency of two-locus genotypes. The triple-dhfr/double-dhps genotype is present in all three regions with frequencies ranging between 30 and 63%, indicating that treatment failure rates are likely to be high.
在坦桑尼亚,经过18年的二线使用后,2001年引入了磺胺多辛和乙胺嘧啶(SP)的抗疟联合用药作为非复杂性疟疾的一线治疗方法。体外对这两种药物的耐药性的遗传决定因素显示为二氢叶酸还原酶基因(dhfr)中7个位点的点突变赋予对乙胺嘧啶的耐药性,以及二氢蝶酸合酶(dhps)基因中5个位点的点突变赋予对磺胺多辛的耐药性。每个基因内不同的突变组合赋予不同程度的不敏感性,但由于多重感染的复杂影响,关于等位基因单倍型出现频率的信息一直缺乏。在这里,我们使用了一种基于高通量序列特异性寡核苷酸探针的新方法来检查坦桑尼亚北部三个恶性疟原虫种群目前的耐药状况。通过对无症状感染进行调查并筛查dhfr和dhps基因中所有已知点突变的存在情况,我们发现仅存在5种dhfr和3种dhps等位基因单倍型。除了等位基因频率存在显著的区域间异质性外,还发现了高频率的三突变dhfr和双突变dhps突变等位基因。体内研究表明,治疗前感染中三个dhfr突变和两个dhps突变同时出现具有统计学上的治疗失败预测性。我们合并了两个位点的数据以确定两位点基因型的频率。三dhfr/双dhps基因型在所有三个区域均存在,频率在30%至63%之间,这表明治疗失败率可能很高。