Strategies for understanding and reducing the Plasmodium vivax and Plasmodium ovale hypnozoite reservoir in Papua New Guinean children: a randomised placebo-controlled trial and mathematical model

Background: The undetectable hypnozoite reservoir for relapsing Plasmodium vivax and P. ovale malarias presents a major challenge for malaria control and elimination in endemic countries. This study aims to directly determine the contribution of relapses to the burden of P. vivax and P. ovale infection, illness, and transmission in Papua New Guinean children. Methods and Findings: From 17 August 2009 to 20 May 2010, 524 children aged 5–10 y from East Sepik Province in Papua New Guinea (PNG) participated in a randomised double-blind placebo-controlled trial of blood- plus liver-stage drugs (chloroquine [CQ], 3 d; artemether-lumefantrine [AL], 3 d; and primaquine [PQ], 20 d, 10 mg/kg total dose) (261 children) or blood-stage drugs only (CQ, 3 d; AL, 3 d; and placebo [PL], 20 d) (263 children). Participants, study staff, and investigators were blinded to the treatment allocation. Twenty children were excluded during the treatment phase (PQ arm: 14, PL arm: 6), and 504 were followed actively for 9 mo. During the follow-up time, 18 children (PQ arm: 7, PL arm: 11) were lost to follow-up. Main primary and secondary outcome measures were time to first P. vivax infection (by qPCR), time to first clinical episode, force of infection, gametocyte positivity, and time to first P. ovale infection (by PCR). A basic stochastic transmission model was developed to estimate the potential effect of mass drug administration (MDA) for the prevention of recurrent P. vivax infections. Targeting hypnozoites through PQ treatment reduced the risk of having at least one qPCR-detectable P. vivax or P. ovale infection during 8 mo of follow-up (P. vivax: PQ arm 0.63/y versus PL arm 2.62/y, HR = 0.18 [95% CI 0.14, 0.25], p < 0.001; P. ovale: 0.06 versus 0.14, HR = 0.31 [95% CI 0.13, 0.77], p = 0.011) and the risk of having at least one clinical P. vivax episode (HR = 0.25 [95% CI 0.11, 0.61], p = 0.002). PQ also reduced the molecular force of P. vivax blood-stage infection in the first 3 mo of follow-up (PQ arm 1.90/y versus PL arm 7.75/y, incidence rate ratio [IRR] = 0.21 [95% CI 0.15, 0.28], p < 0.001). Children who received PQ were less likely to carry P. vivax gametocytes (IRR = 0.27 [95% CI 0.19, 0.38], p < 0.001). PQ had a comparable effect irrespective of the presence of P. vivax blood-stage infection at the time of treatment (p = 0.14). Modelling revealed that mass screening and treatment with highly sensitive quantitative real-time PCR, or MDA with blood-stage treatment alone, would have only a transient effect on P. vivax transmission levels, while MDA that includes liver-stage treatment is predicted to be a highly effective strategy for P. vivax elimination. The inclusion of a directly observed 20-d treatment regime maximises the efficiency of hypnozoite clearance but limits the generalisability of results to real-world MDA programmes. Conclusions: These results suggest that relapses cause approximately four of every five P. vivax infections and at least three of every five P. ovale infections in PNG children and are important in sustaining transmission. MDA campaigns combining blood- and liver-stage treatment are predicted to be a highly efficacious intervention for reducing P. vivax and P. ovale transmission.

研究背景：导致间日疟原虫（Plasmodium vivax）和卵形疟原虫（Plasmodium ovale）疟疾复发的不可检测休眠子（hypnozoite）库，是流行国家开展疟疾防控与消除工作面临的重大挑战。本研究旨在直接明确复发行为对巴布亚新几内亚（Papua New Guinea, PNG）儿童感染间日疟原虫、卵形疟原虫后的疾病负担及传播的贡献程度。方法与研究结果：2009年8月17日至2010年5月20日期间，来自巴布亚新几内亚东塞皮克省的524名5~10岁儿童参与了一项随机双盲安慰剂对照试验，受试儿童被分为两组：红内期联合红外期药物治疗组（261名儿童），给药方案为氯喹（chloroquine, CQ）3天疗程、蒿甲醚-苯芴醇（artemether-lumefantrine, AL）3天疗程以及伯氨喹（primaquine, PQ）20天疗程（总剂量10mg/kg）；单纯红内期药物治疗组（263名儿童），给药方案为氯喹3天疗程、蒿甲醚-苯芴醇3天疗程以及安慰剂（placebo, PL）20天疗程。研究参与者、研究人员及试验研究者均对治疗分组分配情况设盲。治疗阶段共有20名儿童被排除出试验（伯氨喹组14名，安慰剂组6名），最终504名儿童接受了为期9个月的主动随访。随访期间共有18名儿童失访（伯氨喹组7名，安慰剂组11名）。本研究的主要及次要结局指标包括：首次检测到间日疟原虫感染的时间（采用实时定量聚合酶链反应（qPCR））、首次临床发作时间、感染压力、配子体阳性率以及首次检测到卵形疟原虫感染的时间（采用聚合酶链反应（PCR））。本研究构建了基础随机传播模型，以评估大规模药物治疗（mass drug administration, MDA）对预防复发性间日疟原虫感染的潜在效果。通过伯氨喹治疗靶向清除休眠子，可降低受试者在8个月随访期间至少发生1次qPCR检测阳性的间日疟原虫或卵形疟原虫感染的风险（间日疟原虫：伯氨喹组0.63次/年，安慰剂组2.62次/年，风险比（HR）=0.18，95%置信区间（CI）0.14~0.25，p<0.001；卵形疟原虫：0.06次/年 vs 0.14次/年，HR=0.31，95%CI 0.13~0.77，p=0.011），同时可降低至少发生1次临床间日疟发作的风险（HR=0.25，95%CI 0.11~0.61，p=0.002）。伯氨喹还可降低受试者在随访前3个月内的间日疟原虫红内期感染的分子感染压力（伯氨喹组1.90次/年，安慰剂组7.75次/年，发病比率（IRR）=0.21，95%CI 0.15~0.28，p<0.001）。接受伯氨喹治疗的儿童携带间日疟原虫配子体的概率更低（IRR=0.27，95%CI 0.19~0.38，p<0.001）。无论受试者在治疗时是否存在间日疟原虫红内期感染，伯氨喹的治疗效果均无显著差异（p=0.14）。模型分析显示，采用高灵敏度实时定量聚合酶链反应进行大规模筛查与治疗，或仅采用红内期药物治疗的大规模药物治疗，仅会对间日疟原虫的传播水平产生短暂影响；而包含红外期治疗的大规模药物治疗，则被预测为实现间日疟原虫消除的高效策略。采用直接督导下的20天治疗方案可最大化休眠子清除效率，但也限制了本研究结果在真实世界大规模药物治疗项目中的推广性。研究结论：本研究结果表明，在巴布亚新几内亚儿童中，约每5例间日疟原虫感染中就有4例由复发导致，每5例卵形疟原虫感染中至少有3例由复发导致，复发行为在维持疟疾传播过程中发挥重要作用。包含红内期与红外期治疗的大规模药物治疗策略，被预测为降低间日疟原虫和卵形疟原虫传播的高效干预手段。