Table_1_Application of 23 Novel Serological Markers for Identifying Recent Exposure to Plasmodium vivax Parasites in an Endemic Population of Western Thailand.XLSX

Thailand is aiming for malaria elimination by the year 2030. However, the high proportion of asymptomatic infections and the presence of the hidden hypnozoite stage of Plasmodium vivax are impeding these efforts. We hypothesized that a validated surveillance tool utilizing serological markers of recent exposure to P. vivax infection could help to identify areas of ongoing transmission. The objective of this exploratory study was to assess the ability of P. vivax serological exposure markers to detect residual transmission “hot-spots” in Western Thailand. Total IgG levels were measured against a panel of 23 candidate P. vivax serological exposure markers using a multiplexed bead-based assay. A total of 4,255 plasma samples from a cross-sectional survey conducted in 2012 of endemic areas in the Kanchanaburi and Ratchaburi provinces were assayed. We compared IgG levels with multiple epidemiological factors that are associated with an increased risk of P. vivax infection in Thailand, including age, gender, and spatial location, as well as Plasmodium infection status itself. IgG levels to all proteins were significantly higher in the presence of a P. vivax infection (n = 144) (T-test, p < 0.0001). Overall seropositivity rates varied from 2.5% (PVX_097625, merozoite surface protein 8) to 16.8% (PVX_082670, merozoite surface protein 7), with 43% of individuals seropositive to at least 1 protein. Higher IgG levels were associated with older age (>18 years, p < 0.05) and males (17/23 proteins, p < 0.05), supporting the paradigm that men have a higher risk of infection than females in this setting. We used a Random Forests algorithm to predict which individuals had exposure to P. vivax parasites in the last 9-months, based on their IgG antibody levels to a panel of eight previously validated P. vivax proteins. Spatial clustering was observed at the village and regional level, with a moderate correlation between PCR prevalence and sero-prevalence as predicted by the algorithm. Our data provides proof-of-concept for application of such surrogate markers as evidence of recent exposure in low transmission areas. These data can be used to better identify geographical areas with asymptomatic infection burdens that can be targeted in elimination campaigns.

泰国计划于2030年实现疟疾消除（malaria elimination）。然而，无症状感染的高占比以及间日疟原虫（Plasmodium vivax）潜藏的休眠子（hypnozoite）阶段，正阻碍这一目标的推进。我们提出假说：一款经验证的、利用间日疟原虫近期感染血清学标志物的监测工具，或可助力识别持续传播的区域。本探索性研究旨在评估间日疟原虫血清学暴露标志物检测泰国西部残留传播“热点区域”的能力。研究采用基于微球的多重检测技术（multiplexed bead-based assay），针对一组23种候选间日疟原虫血清学暴露标志物检测总IgG水平。本研究共纳入2012年在泰国甘烹碧府（Kanchanaburi）和叻丕府（Ratchaburi）疟疾流行区开展的横断面调查（cross-sectional survey）所收集的4255份血浆样本进行检测。我们将IgG水平与多项与泰国间日疟原虫感染风险升高相关的流行病学因素进行了对比，包括年龄、性别、空间位置以及疟原虫感染状态本身。在间日疟原虫感染个体（n=144）中，所有靶蛋白对应的IgG水平均显著升高（T检验，p<0.0001）。总体血清阳性率（seropositivity rates）介于2.5%（PVX_097625，裂殖子表面蛋白8（merozoite surface protein 8））至16.8%（PVX_082670，裂殖子表面蛋白7（merozoite surface protein 7））之间，其中43%的个体至少对1种蛋白呈血清阳性。更高的IgG水平与年龄较大（>18岁，p<0.05）和男性（17/23种蛋白，p<0.05）相关，印证了该研究场景下男性感染风险高于女性的学术范式。我们基于8种已验证的间日疟原虫蛋白的IgG抗体水平，采用随机森林（Random Forests）算法预测个体在过去9个月内是否暴露于间日疟原虫。研究在村落和区域层面观察到空间聚集现象，算法预测的聚合酶链式反应（PCR）患病率与血清阳性率之间存在中等程度的相关性。本研究为这类替代标志物作为低传播区域近期暴露证据的应用提供了概念验证。这些数据可用于更精准地识别存在无症状感染负担的地理区域，从而为疟疾消除行动中的靶向干预提供支撑。