Maze Emmanuel A, Booth George, Limon Georgina, Belij-Rammerstorfer Sandra, Tchakarova Simona R, Alexandrov Tsviatko, Browning Clare, Wilsden Ginette, Ludi Anna B, Charleston Bryan, Lambe Teresa
The Pirbright Institute, Woking, United Kingdom.
Oxford Vaccine Group, Department of Paediatrics, University of Oxford, Oxford, United Kingdom.
Front Immunol. 2025 Jan 20;15:1423474. doi: 10.3389/fimmu.2024.1423474. eCollection 2024.
Crimean-Congo haemorrhagic fever virus (CCHFV) and Nairobi sheep disease virus (NSDV) are orthonairoviruses of concern, able to cause haemorragic fever disease in humans and sheep, respectively. CCHFV and NSDV cocirculating in small ruminant populations across South Asia and East Africa. Cross-reactivity to viruses of the Orthonairovirus genus can potentially interfere with serological assays when employed for serosurveillance in regions where two or more genus members overlap in their distribution.
In this study, sheep sera sampled from a region of confirmed CCHFV circulation and NSDV absence were utilized, thereby eliminating the possibility of co-exposure. Field sera were tested against in-house anti-NSDV ELISAs specific to the nucleoprotein (NSDV NP) and glycoprotein C (NSDV Gc) antigens as well as an in-house NSDV 80% plaque reduction neutralization test (PRNT). We assessed whether there is a correlation between CCHFV- and NSDV-specific ELISAs. Furthermore, epitopes-derived from CCHFV antigens for sheep antibody that were available from the literature were analyzed.
When comparing NSDV antigen-specific antibody responses against previously tested CCHFV antigen-specific antibody responses, a strong positive correlation was observed between the Gc-specific responses, while a weak positive correlation was observed between the NP-specific responses. Consequently, NP-specific ELISAs have a higher assay specificity compared to Gc-specific ELISAs, making them more suitable for serosurveillance in regions where multiple orthonairoviruses co-circulate. Crucially, only one seropositive sample to NSDV Gc-specific out of a set of 224 (0.4%) showed a neutralizing capacity at the lowest serum dilution (1:8), suggesting these field sera have not been exposed to NSDV. Based on an analysis of known epitopes in NP targeted by antibodies in sheep serum, we propose that NP is less cross-reactive because dominant epitopes are highly dissimilar between CCHFV and NSDV.
Gc exhibited a strong cross-reaction while the NP was weakly cross-reactive due to dominant epitopes being highly dissimilar between CCHFV and NSDV. Our in-house PRNT80 assay can could be used as a confirmatory test in regions where CCHFV and NSDV circulate.
克里米亚-刚果出血热病毒（CCHFV）和内罗毕羊病病毒（NSDV）是备受关注的正布尼亚病毒，分别可导致人类出血热疾病和绵羊发病。CCHFV和NSDV在南亚和东非的小型反刍动物群体中共同传播。当在两种或更多种该病毒属成员分布重叠的地区进行血清学监测时，对正布尼亚病毒属病毒的交叉反应可能会干扰血清学检测。
在本研究中，使用了从已确认CCHFV传播但不存在NSDV的地区采集的绵羊血清，从而排除了共同暴露的可能性。用针对核蛋白（NSDV NP）和糖蛋白C（NSDV Gc）抗原的自制抗NSDV酶联免疫吸附测定（ELISA）以及自制的NSDV 80%蚀斑减少中和试验（PRNT）检测现场血清。我们评估了CCHFV特异性ELISA和NSDV特异性ELISA之间是否存在相关性。此外，还分析了文献中可获得的源自CCHFV抗原的绵羊抗体表位。
将NSDV抗原特异性抗体反应与先前检测的CCHFV抗原特异性抗体反应进行比较时，发现Gc特异性反应之间存在强正相关，而NP特异性反应之间存在弱正相关。因此，与Gc特异性ELISA相比，NP特异性ELISA具有更高的检测特异性，使其更适合在多种正布尼亚病毒共同传播的地区进行血清学监测。至关重要的是，在224份样本中，只有1份（0.4%）对NSDV Gc特异性呈血清阳性的样本在最低血清稀释度（1:8）时显示出中和能力，这表明这些现场血清未接触过NSDV。基于对绵羊血清中抗体靶向的NP中已知表位的分析，我们认为NP的交叉反应性较低，因为CCHFV和NSDV之间的主要表位高度不同。
由于CCHFV和NSDV之间的主要表位高度不同，Gc表现出强烈的交叉反应，而NP表现出较弱的交叉反应。我们的自制PRNT80检测可在CCHFV和NSDV传播的地区用作确证试验。
