Laboratório de Malária, Centro de Pesquisas René Rachou, FIOCRUZ, Av, Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brazil.
Malar J. 2014 Feb 28;13:73. doi: 10.1186/1475-2875-13-73.
Chloroquine (CQ), a cost effective antimalarial drug with a relatively good safety profile and therapeutic index, is no longer used by itself to treat patients with Plasmodium falciparum due to CQ-resistant strains. P. vivax, representing over 90% of malaria cases in Brazil, despite reported resistance, is treated with CQ as well as with primaquine to block malaria transmission and avoid late P. vivax malaria relapses. Resistance to CQ and other antimalarial drugs influences malaria control, thus monitoring resistance phenotype by parasite genotyping is helpful in endemic areas.
A total of 47 P. vivax and nine P. falciparum fresh isolates were genetically characterized and tested for CQ, mefloquine (MQ) and artesunate (ART) susceptibility in vitro. The genes mdr1 and pfcrt, likely related to CQ resistance, were analyzed in all isolates. Drug susceptibility was determined using short-term parasite cultures of ring stages for 48 to 72 hour and thick blood smears counts. Each parasite isolate was tested with the antimalarials to measure the geometric mean of 50% inhibitory concentration.
The low numbers of P. falciparum isolates reflect the species prevalence in Brazil; most displayed low sensitivity to CQ (IC50 70 nM). However, CQ resistance was rare among P. vivax isolates (IC50 of 32 nM). The majority of P. vivax and P. falciparum isolates were sensitive to ART and MQ. One hundred percent of P. falciparum isolates carried non-synonymous mutations in the pfmdr1 gene in codons 184, 1042 and 1246, 84% in codons 1034 and none in codon 86, a well-known resistance mutation. For the pfcrt gene, mutations were observed in codons 72 and 76 in all P. falciparum isolates. One P. falciparum isolate from Angola, Africa, showing sensitivity to the antimalarials, presented no mutations. In P. vivax, mutations of pvmdr1 and the multidrug resistance gene 1 marker at codon F976 were absent.
All P. falciparum Brazilian isolates showed CQ resistance and presented non-synonymous mutations in pfmdr1 and pfcrt. CQ resistant genotypes were not present among P. vivax isolates and the IC50 values were low in all samples of the Brazilian West Amazon.
氯喹（CQ）是一种具有相对良好的安全性和治疗指数的廉价抗疟药物，由于出现耐氯喹疟原虫株，不再单独用于治疗恶性疟原虫感染。尽管有报道称存在耐药性，但巴西超过 90%的疟疾病例是由间日疟原虫引起的，仍用 CQ 联合伯氨喹来阻断疟疾传播并避免迟发性间日疟复发。CQ 和其他抗疟药物的耐药性影响疟疾的控制，因此通过寄生虫基因分型监测耐药表型有助于在流行地区进行。
对 47 株间日疟原虫和 9 株恶性疟原虫新鲜分离株进行基因特征分析，并在体外检测 CQ、甲氟喹（MQ）和青蒿琥酯（ART）敏感性。对所有分离株进行 mdr1 和 pfcrt 基因分析，这些基因可能与 CQ 耐药有关。采用环期短时间寄生虫培养法（48 至 72 小时）和厚血涂片计数来测定药物敏感性。用各种抗疟药物对每个寄生虫分离株进行检测，以测量 50%抑制浓度的几何平均值。
恶性疟原虫分离株数量较少，反映了巴西该物种的流行情况；大多数恶性疟原虫分离株对 CQ 敏感性较低（IC50 为 70 nM）。然而，间日疟原虫分离株的 CQ 耐药性罕见（IC50 为 32 nM）。大多数间日疟原虫和恶性疟原虫分离株对 ART 和 MQ 敏感。100%的恶性疟原虫分离株在 pfmdr1 基因的 184、1042 和 1246 密码子处发生非同义突变，84%在 1034 密码子处发生突变，而在 86 密码子处无突变，这是一个众所周知的耐药突变。在 pfcrt 基因中，所有恶性疟原虫分离株在 72 和 76 密码子处均发生突变。来自非洲安哥拉的 1 株恶性疟原虫分离株对这些抗疟药物敏感，但没有突变。在间日疟原虫中，pvmdr1 和多药耐药基因 1 标记物的 F976 密码子突变缺失。
所有巴西恶性疟原虫分离株均表现出 CQ 耐药性，并在 pfmdr1 和 pfcrt 基因中发生非同义突变。间日疟原虫分离株不存在 CQ 耐药基因型，巴西西亚马逊地区所有样本的 IC50 值均较低。
