Characteristics of positive tests.

BackgroundLymphatic filariasis (LF) is a parasitic disease-causing severe pain, disfiguring, and disabling clinical conditions such as lymphoedema and hydrocoele that are associated with morbidity and stigma. The disease has been targeted for global elimination with the annual mass drug administration (MDA) strategy. We have evaluated the need to implement mass drug administration against W. bancrofti infection in urban zones of Monrovia using both serology and molecular Xenomonitoring (XM).MethodologyConfirmatory mapping protocols recommended by WHO were carried out in the four health districts of Monrovia. Schools were selected using probability proportionate to size (PPS) and eligible children aged 9–14 years were tested for circulating filarial antigen (CFA) using an Alere Filariasis Test Strip (FTS). Health Districts were assessed as requiring MDA if they exceeded the critical cut off of 3 positive tests corresponding to CFA ≥ 2%. Two health districts were selected for entomological investigations based on pre-disposing risk factors for mosquitoes. Mosquito collection was carried out using exit traps (ETs) and gravid trap (GTs) for 6 months. Mosquitos were tested for W. bancrofti DNA using qPCR.Principal findingsNinety-six children in the sample had a positive serology test result, with a mean CFA prevalence of 5.3% (95% CI: 4.4 - 6.5%). All four health districts exceeded the critical cut off of 3 cases and in Somalia Drive there were 59 positive tests. In Central Monrovia which had 4 cases, 2 of them are likely locally imported from Somalia Drive where the children reported living. A total of 19,355 potential vector mosquitoes were collected, of which 84.4% (16,335) were Culex and 16.6% (3,020) An. gambiae. All mosquitoes were analyzed, and none were found to be infected with W. bancrofti.ConclusionMDA is required in three health districts of Monrovia. Confirmatory mapping protocols require adaptation for urban settings. The sampling strategy for the XM was unable to identify transmission in this case and requires further research to optimise it for informing MDA implementation decisions.

背景：淋巴丝虫病（Lymphatic filariasis, LF）是一种寄生虫病，可引发剧烈疼痛、毁容性及致残性临床病症，例如淋巴水肿与鞘膜积液，这类病症会伴随发病负担与社会污名。该疾病已被纳入全球消除计划，采用年度集体药物发放（mass drug administration, MDA）策略。本研究通过血清学与分子生物学媒传监测（Xenomonitoring, XM）两种手段，评估了蒙罗维亚城区针对班氏吴策线虫（Wuchereria bancrofti, W. bancrofti）感染实施集体药物发放的必要性。

方法：本研究遵循世界卫生组织（World Health Organization, WHO）推荐的确证制图流程，在蒙罗维亚的四个卫生区开展工作。采用按规模比例抽样（probability proportionate to size, PPS）方法选取学校，对年龄9~14岁的合格儿童使用Alere丝虫病检测试纸（Alere Filariasis Test Strip, FTS）检测循环丝虫抗原（circulating filarial antigen, CFA）。若某卫生区的阳性检测数超过临界阈值（对应CFA阳性率≥2%的3例阳性样本），则判定该区域需要实施MDA。基于蚊虫传播的易感风险因素，选取两个卫生区开展昆虫学调查。使用出口诱捕器（exit traps, ETs）与孕蚊诱捕器（gravid trap, GTs）进行了为期6个月的蚊虫采集。采用实时定量聚合酶链反应（quantitative PCR, qPCR）检测蚊虫体内的班氏吴策线虫DNA。

主要结果：本次研究样本中共96名儿童血清学检测呈阳性，平均CFA阳性率为5.3%（95%置信区间：4.4~6.5%）。四个卫生区的阳性检测数均超过3例的临界阈值，其中索马里大道区域共检出59例阳性样本。蒙罗维亚中部区域检出4例阳性，其中2例大概率为输入性病例，患儿自述居住地为索马里大道区域。本次研究共采集到19355只潜在媒介蚊虫，其中84.4%（16335只）为库蚊，16.6%（3020只）为冈比亚按蚊（Anopheles gambiae, An. gambiae）。对所有蚊虫进行检测后，未检出班氏吴策线虫感染阳性的样本。

结论：蒙罗维亚的三个卫生区需实施MDA。确证制图流程需针对城区环境进行优化调整。本次媒传监测的采样策略未能检出本研究中的传播事件，需开展进一步研究以优化该策略，为MDA实施决策提供依据。