Performance of novel onchocerciasis rapid diagnostic tests in a field setting in South Sudan

Introduction Onchocerciasis is a neglected tropical disease caused by Onchocerca volvulus and is primarily controlled through mass drug administration (MDA) of ivermectin. Current diagnostic tests perform sub-optimally for onchocerciasis elimination programs. According to the WHO, a test needs a sensitivity of ≥60% and a specificity of ≥99.8% for mapping, and a sensitivity of ≥89% and a specificity of ≥99.8% for MDA stopping decisions. We assessed the performance of the commercially available Ov16 SD Bioline rapid diagnostic test (RDT) and three novel RDTs: DDTD biplex type A, type C, and the monoplex type GADx. Methods The study included 319 pregnant/post-partum women in Maridi, an onchocerciasis-endemic area in South Sudan. Locally trained healthcare workers conducted RDT with whole blood and skin snip testing. Ov16 SD Bioline RDT was also performed using dried blood spots (DBS). Diagnostic performances were evaluated using three individual reference tests (anti-Ov16 ELISA, O-150 qPCR, skin snip microscopy) and two composite reference standards. DBS were tested for Mansonella spp. using qPCR to account for potential false positives. Results Anti-Ov16 ELISA detected O. volvulus antibodies in 49.6% (123/248) participants, while O. volvulus infection was documented by skin snip microscopy in 31.9% (46/144) participants and in 41.8% (50/141) by qPCR. Mansonella spp. infection prevalence was 13.4% (34/253). Monoplex RTDs (Ov16 SD Bioline, GADx) detected O. volvulus antibodies in >60%, while the biplex tests (DDTD A and C) detected 50% seropositivity. Estimated sensitivities of RDTs ranged from 69.4% (Ov16 SD Bioline) to 48.9% (DDTD A), while specificity ranged from 73.2% (DDTD C) to 42.5% (Ov16 SD Bioline). Conclusion O. volvulus and Mansonella spp. prevalence was high among pregnant and post-partum women in Maridi. The novel RDTs demonstrated sensitivities within the range of the commercially available Ov16 SD Bioline RDT, meeting the WHO threshold for onchocerciasis mapping but not for MDA stopping decisions. No RDT met the specificity threshold of 99.8%, although some exhibited slightly higher specificity than Ov16 SD Bioline RDT. This suboptimal specificity raises concerns, underscoring the need for better diagnostic tools to support onchocerciasis elimination efforts.引言 盘尾丝虫病（Onchocerciasis）是一种由旋盘尾丝虫（Onchocerca volvulus）引发的被忽视热带病，当前主要通过伊维菌素大规模药物给药（mass drug administration, MDA）开展防控。现有诊断检测方法在盘尾丝虫病消除项目中的表现未达理想水平。据世界卫生组织（World Health Organization, WHO）规定，用于流行区划界的检测试剂需满足灵敏度≥60%、特异度≥99.8%，而用于判定是否停止大规模药物给药的检测试剂则需灵敏度≥89%、特异度≥99.8%。本研究评估了市售Ov16 SD Bioline快速诊断检测（rapid diagnostic test, RDT）及三款新型快速诊断检测试剂的性能：DDTD双联A型、DDTD双联C型，以及单联GADx试剂。 方法 本研究纳入了南苏丹盘尾丝虫病流行区马里迪的319名妊娠/产后女性。经当地培训的医护人员采用全血样本开展快速诊断检测，并实施皮肤微丝蚴检测；同时采用干血斑（dried blood spots, DBS）样本进行Ov16 SD Bioline快速诊断检测。本研究采用三项独立参考检测方法——抗Ov16酶联免疫吸附试验（anti-Ov16 enzyme-linked immunosorbent assay, anti-Ov16 ELISA）、O-150实时荧光定量聚合酶链式反应（O-150 quantitative polymerase chain reaction, O-150 qPCR）及皮肤微丝蚴镜检——以及两项复合参考标准，对诊断性能进行评估。此外，研究采用实时荧光定量聚合酶链式反应对干血斑样本进行曼森线虫属（Mansonella spp.）检测，以排查潜在假阳性结果。 结果 抗Ov16酶联免疫吸附试验在49.6%（123/248）的受试者中检出旋盘尾丝虫抗体；皮肤微丝蚴镜检在31.9%（46/144）的受试者中确诊旋盘尾丝虫感染，实时荧光定量聚合酶链式反应则在41.8%（50/141）的受试者中检出该感染。曼森线虫属感染的患病率为13.4%（34/253）。单联快速诊断检测试剂（Ov16 SD Bioline、GADx）在超过60%的样本中检出旋盘尾丝虫抗体，而双联检测试剂（DDTD A与C）的血清阳性检出率为50%。各快速诊断检测试剂的估算灵敏度介于48.9%（DDTD A）至69.4%（Ov16 SD Bioline）之间，特异度则介于42.5%（Ov16 SD Bioline）至73.2%（DDTD C）之间。 结论 马里迪地区妊娠及产后女性的旋盘尾丝虫与曼森线虫属感染率较高。新型快速诊断检测试剂的灵敏度处于市售Ov16 SD Bioline快速诊断检测试剂的区间范围内，满足世界卫生组织针对盘尾丝虫病流行区划界的阈值要求，但未达到判定停止大规模药物给药的阈值标准。所有快速诊断检测试剂均未达到99.8%的特异度阈值，尽管部分试剂的特异度略高于Ov16 SD Bioline快速诊断检测试剂。该特异度未达理想水平的情况令人担忧，凸显了开发更优质诊断工具以支撑盘尾丝虫病消除工作的必要性。