Shirato Kazuya, Melaku Simenew Keskes, Kawachi Kengo, Nao Naganori, Iwata-Yoshikawa Naoko, Kawase Miyuki, Kamitani Wataru, Matsuyama Shutoku, Tessema Tesfaye Sisay, Sentsui Hiroshi
Department of Virology III, National Institute of Infectious Diseases, Musashimurayama, Japan.
Department of Biotechnology, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia.
Front Microbiol. 2019 Jun 19;10:1326. doi: 10.3389/fmicb.2019.01326. eCollection 2019.
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（MERS）是一种由中东呼吸综合征冠状病毒（MERS-CoV）引起的新发呼吸道疾病。自2012年以来，MERS在沙特阿拉伯呈地方流行。MERS-CoV的宿主是单峰骆驼，这表明MERS主要是一种人畜共患病。在整个中东、北非和东非，单峰骆驼中普遍存在MERS-CoV，针对MERS-CoV的中和抗体证明了这一点；然而，人类病例仍局限于中东地区。为了更好地理解这种差异的原因，基于埃塞俄比亚的刺突（S）蛋白对非洲骆驼MERS-CoV的病毒学特性进行了分析。从埃塞俄比亚阿法尔地区的258头年轻单峰骆驼（≤2岁）中采集鼻拭子，经基因检测，其中39头MERS-CoV呈阳性。所有阳性检测均仅限于阿米巴拉县。使用二代测序技术，成功解码了阿米巴拉分离株的两个全长基因组；根据全长和S蛋白序列的系统发育分析，这两个分离株均属于C2分支。然后构建了重组MERS-CoV EMC分离株，其中S蛋白被阿米巴拉分离株的S蛋白取代，以测试这些蛋白在病毒特性中的作用。阿米巴拉S重组体在培养细胞中的复制速度比EMC S重组体慢。在中和试验中，相对于EMC S重组体，阿米巴拉S重组体被来自埃塞俄比亚单峰骆驼和EMC分离株（野生型）免疫小鼠血清的较低浓度血清中和，这表明包被有阿米巴拉S蛋白的病毒比EMC S蛋白更容易被中和。使用EMC和阿米巴拉S蛋白的S1/S2嵌合重组体进行的中和实验表明，中和谱取决于S蛋白的S1区域。这些结果表明，埃塞俄比亚MERS-CoV中观察到的病毒复制较慢和易于中和是由于S蛋白的菌株特异性差异，这可能是埃塞俄比亚没有人类MERS-CoV病例的原因。
