Data_Sheet_1_Middle East Respiratory Syndrome Coronavirus in Dromedaries in Ethiopia Is Antigenically Different From the Middle East Isolate EMC.PDF

Middle East respiratory syndrome (MERS) is an emerging respiratory disease caused by the MERS coronavirus (MERS-CoV). MERS has been endemic to Saudi Arabia since 2012. The reservoir of MERS-CoV is the dromedary camel, suggesting that MERS is primarily a zoonotic disease. MERS-CoV is common in dromedaries throughout the Middle East, North Africa, and East Africa as evidenced by neutralizing antibodies against MERS-CoV; however, human cases have remained limited to the Middle East. To better understand the cause of this difference, the virological properties of African camel MERS-CoV were analyzed based on the spike (S) protein in Ethiopia. Nasal swabs were collected from 258 young dromedaries (≤ 2 years old) in the Afar region of Ethiopia, of which 39 were positive for MERS-CoV, as confirmed by genetic tests. All positive tests were exclusive to the Amibara woreda region. Using next-generation sequencing, two full-length genomes of Amibara isolates were successfully decoded; both isolates belonged to the C2 clade based on phylogenetic analysis of full-length and S protein sequences. Recombinant EMC isolates of MERS-CoV, in which the S protein is replaced with those of Amibara isolates, were then generated to test the roles of these proteins in viral properties. Amibara S recombinants replicated more slowly in cultured cells than in EMC S recombinants. In neutralizing assays, Amibara S recombinants were neutralized by lower concentrations of sera from both Ethiopian dromedaries and EMC isolate (wild-type)-immunized mouse sera, relative to the EMC S recombinants, indicating that viruses coated in the Amibara S protein were easier to neutralize than the EMC S protein. Neutralization experiments performed using S1/S2 chimeric recombinants of the EMC and Amibara S proteins showed that the neutralization profile was dependent on the S1 region of the S protein. These results suggest that the slower viral replication and the ease of neutralization seen in the Ethiopian MERS-CoV are due to strain-specific differences in the S protein and may account for the absence of human MERS-CoV cases in Ethiopia.

中东呼吸综合征（Middle East respiratory syndrome, MERS）是一种由中东呼吸综合征冠状病毒（MERS coronavirus, MERS-CoV）引发的新发呼吸道传染病。自2012年起，沙特阿拉伯便成为MERS的地方性流行区域。MERS-CoV的自然储存宿主为单峰驼，提示MERS主要为人畜共患病。从中东、北非至东非的单峰驼种群中均广泛存在MERS-CoV，这一点可通过针对MERS-CoV的中和抗体检测结果得到验证，但人类感染病例仍仅局限于中东地区。为进一步阐明此类地域差异的成因，研究团队以埃塞俄比亚境内单峰驼所携带的MERS-CoV刺突（spike, S）蛋白为研究靶点，对其病毒学特性展开分析。研究人员在埃塞俄比亚阿法尔地区采集了258只≤2岁幼年单峰驼的鼻拭子样本，经基因检测确认其中39份样本MERS-CoV呈阳性，且所有阳性样本均仅分布于阿米巴拉沃雷达（Amibara woreda）地区。随后，研究人员借助下一代测序技术成功解码出2株阿米巴拉分离株的全长基因组；通过对全长基因组及S蛋白序列开展系统发育分析，确认这2株分离株均隶属于C2进化枝。为探究此类S蛋白在病毒特性中的功能作用，研究团队构建了重组MERS-CoV EMC分离株，将其原有的S蛋白替换为阿米巴拉分离株的S蛋白。细胞培养实验结果显示，携带阿米巴拉S蛋白的重组病毒的复制速率显著慢于携带EMC S蛋白的重组病毒。中和试验结果表明，相较于携带EMC S蛋白的重组病毒，埃塞俄比亚单峰驼血清以及EMC分离株（野生型）免疫小鼠血清在更低浓度下即可中和携带阿米巴拉S蛋白的重组病毒，这提示包被阿米巴拉S蛋白的病毒比包被EMC S蛋白的病毒更易被中和。利用EMC与阿米巴拉S蛋白的S1/S2嵌合重组病毒开展的中和实验显示，病毒的中和谱系取决于S蛋白的S1区域。上述研究结果表明，埃塞俄比亚MERS-CoV所表现出的复制速率较慢且易被中和的特性，源于其S蛋白的毒株特异性差异，这或许可以解释为何埃塞俄比亚未出现人类MERS-CoV感染病例。