Evaluating the determinants of the spread of COVID-19 between and within rural communities in Mali, West Africa based on blood-fed mosquitoes

基于吸血蚊子评估西非马里农村社区之间和内部 COVID-19 传播的决定因素

• 批准号: 10927969
• 负责人: Tovi Lehmann
• 金额: $ 115.57万
• 依托单位: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10927969
• 关键词: 2019-nCoV; 3 year old; Affect; Africa; Africa South of the Sahara; African; Age; Americas; Antibodies; Antibody titer measurement; Antigens; Area; Arteries; Asia; Biological Assay; Blood; Blood specimen; COVID-19; COVID-19 monitoring; Cities; Communities; Country; Culicidae; Data; Disease Surveillance; Distant; Environment; Enzyme-Linked Immunosorbent Assay; Epidemiology; Europe; Exposure to; Female; Goals; Home; Hour; Human; Human Bites; Immunoassay; Immunoglobulin G; Individual; Infection; Laboratories; Mali; Marketing; Measures; Monitor; Nucleocapsid; Paper; Persons; Population; Printing; Process; Protocols documentation; Public Health; Publishing; Rest; Role; Route; Rural; Rural Community; SARS-CoV-2 infection; SARS-CoV-2 transmission; Sampling; Schools; Serology; Seroprevalences; Shapes; Site; Specificity; Specimen; System; Techniques; Time; Transportation; United States National Institutes of Health; Virus; Visit; Widespread Disease; Work; antibody detection; antibody test; aspirate; density; epidemiologic data; epidemiology study; experimental study; feeding; frontier; human disease; novel; pandemic disease; pre-pandemic; receptor binding; rural setting; seropositive; serosurveillance; spatiotemporal; vector-borne

The spread of COVID-19 in rural sub-Saharan Africa is poorly understood and reliable data are unlikely to be obtained as a result of low capacity for disease surveillance, compounded by high proportion of young population that present mostly asymptomatic or low-symptomatic infections. To fill this gap and assess how the unique ecological and cultural settings affect it, we have initiated a novel epidemiological study, monitoring COVID-19 infections by sampling blood-fed mosquitoes collected monthly in houses of 20 Malian villages spread across 500km. By May 2022, a total of 48,805 females mosquitoes were collected over 27,900 house visits from 20 villages. We expect at least 30,000 females being blood-fed. Experiments using these and laboratory mosquitoes were carried out in Mali and in NIH to provide a proof of concept to the feasibility of this project as a prerequisite before expansion to the full scope of this work. Immunoglobulin-G antibodies were found to be readily detectable within the mosquito bloodmeals by a bead-based immunoassay through 10 (and up to 30) hours post-feeding, indicating that most mosquitoes collected via indoor aspiration catches (that likely fed the previous night and are now resting), are viable samples for analysis. Using 90 pre-pandemic bloodfed mosquitoes we established antigen specific cutoffs (mean 5*STD) for antibodies against the i) nucleocapsid, ii) the receptor binding domain (RBD), and iii-iv) the two spike domains, to identify mosquitoes that fed on Covid-seropositive and seronegative humans. By requiring at least 2 antibody titers to exceed their cutoffs the estimated sensitivity was 0.90 (+/=0.059) and specificity was 0.92 (+/-0.080), indicating that most blood-fed mosquitoes collected by early morning indoors, have likely fed the previous night, and are viable samples for analysis. Using this assay, we evaluated the change in sero-prevalence of one urban and four rural communities in Mali. Consistent with, albeit somewhat lower than, a conventional serological study in Mali (Sagara et al. 2021), crude sero-positivity of blood sampled via mosquitoes was 6.3% in October/November 2020 over all sites, and increased to 25.1% overall, with the town closest to Bamako (Sotuba) reaching 46.7% in February of 2021. Adjusted to mosquitoes feeding on non-human hosts and to the possibility of multiple mosquitoes feeding on the same individual human changed the results little because most mosquitoes fed on human blood and relatively small number of mosquitoes were analyzed from each house at a period. In finding this a viable technique amenable to conventional immunoassays to measure population-level sero-prevalance, we feel sero-surveillance of human diseases, regardless if they are vector-borne, is attainable, non-invasive sampling option, especially suited to areas with high density of human-biting mosquitoes. Our first paper (Krajacich et al. 2023) summarizing the results of 5 villages at two time points is currently Under Review in Frontiers in Epidemiology after the preprint was published in medRxiv: https://www.medrxiv.org/content/10.1101/2023.06.13.23291267v1. Additionally, our team in Mali has been performing ELISA assays to detect antibodies against the Spike and RBD based on protocols optimized by the group of Patrick Duffy (LMIV). Currently over 4,000 mosquitoes were assayed for both antigens. Based on cutoffs established for these ELISA assays in Mali (Woodford et al. 2021), overall seroprevalence rates increased from 21.9% in October 2020 to 51.2% in January-February 2021 (21=55.4, P<0.001), in accord with sero-prevalence change measured in resident of 3 Malian communities (Sagara et al. 2022). Note that the assortment of villages used in this study was different from the subset used in the four-antigen bead assay (above). Our goal is to complete the assays on 12,000 blood-fed mosquitoes representing multiple time points from October 2020 to September 2022 from 20 rural communities, which will provide the dynamics of spread of COVID-19 in Mali during the first years of the pandemic.

人们对撒哈拉以南非洲农村地区 COVID-19 的传播知之甚少，而且由于疾病监测能力低下，不太可能获得可靠的数据，再加上年轻人口中大多数无症状或低症状感染的比例很高，因此不太可能获得可靠的数据。为了填补这一空白并评估独特的生态和文化环境对其有何影响，我们启动了一项新颖的流行病学研究，通过每月在绵延 500 公里的 20 个马里村庄的房屋中采集的吸血蚊子样本来监测 COVID-19 感染情况。截至 2022 年 5 月，我们对 20 个村庄进行了 27,900 次入户走访，共收集了 48,805 只雌蚊。我们预计至少有 30,000 名雌性接受血液喂养。在马里和美国国立卫生研究院进行了使用这些蚊子和实验室蚊子的实验，为该项目的可行性提供概念证明，作为扩展到这项工作的全部范围之前的先决条件。 通过基于珠子的免疫测定，在喂食后 10（最多 30）小时内，可以很容易地在蚊子血粉中检测到免疫球蛋白-G 抗体，这表明大多数蚊子是通过室内抽吸捕获物收集的（可能是前一天晚上喂食的，现在正在休息），是用于分析的可行样本。使用 90 只大流行前的吸血蚊子，我们针对 i) 核衣壳、ii) 受体结合结构域 (RBD) 和 iii-iv) 两个尖峰结构域的抗体建立了抗原特异性截止值（平均 5*STD），以识别具有以下特征的蚊子：以新冠病毒血清阳性和血清阴性的人类为食。通过要求至少 2 个抗体滴度超过其临界值，估计的敏感性为 0.90 (+/-0.059)，特异性为 0.92 (+/-0.080)，表明清晨在室内收集的大多数吸血蚊子可能已经喂食了前一天晚上，并且是用于分析的可行样本。 利用这一测定，我们评估了马里一个城市和四个农村社区的血清流行率变化。与马里的一项传统血清学研究（Sagara 等人，2021 年）一致（尽管略低），2020 年 10 月/11 月所有地点通过蚊子采集的血液样本的粗血清阳性率为 6.3%，总体上升至 25.1%，到 2021 年 2 月，最靠近巴马科 (Sotuba) 的城镇达到 46.7%。根据以蚊子为食的蚊子进行了调整非人类宿主以及以同一个人为食的多种蚊子的可能性对结果影响不大，因为大多数蚊子以人类血液为食，并且在一段时间内对每个房屋进行分析的蚊子数量相对较少。在发现这种可行的技术适合传统免疫测定法来测量人群水平的血清流行率时，我们认为对人类疾病的血清监测，无论它们是否是媒介传播的，都是可以实现的、非侵入性采样选择，特别适合于有疾病的地区。叮咬人类的蚊子密度很高。我们的第一篇论文（Krajacich 等人，2023 年）总结了 5 个村庄在两个时间点的结果，预印本在 medRxiv 上发表后，目前正在流行病学前沿进行审查：https://www.medrxiv.org/content/10.1101/ 2023.06.13.23291267v1。 此外，我们在马里的团队一直在根据 Patrick Duffy (LMIV) 小组优化的方案进行 ELISA 检测，以检测针对 Spike 和 RBD 的抗体。目前，对 4,000 多只蚊子进行了这两种抗原的检测。根据在马里为这些 ELISA 测定确定的临界值（Woodford 等人，2021 年），总体血清阳性率从 2020 年 10 月的 21.9% 增加到 2021 年 1 月至 2 月的 51.2%（21=55.4，P<0.001），与血清一致- 在 3 个马里社区居民中测量的患病率变化（Sagara 等，2017） 2022）。请注意，本研究中使用的村庄分类与四抗原珠测定（上文）中使用的子集不同。我们的目标是完成对 2020 年 10 月至 2022 年 9 月多个时间点的 12,000 只吸血蚊子的检测，这些蚊子来自 20 个农村社区，这将提供大流行最初几年马里的 COVID-19 传播动态。