Genomics and zoonotic infections: Middle East respiratory syndrome

The emergence of Middle East respiratory syndrome (MERS) and the discovery of MERS coronavirus (MERS-CoV) in 2012 suggests that another SARS-like epidemic is occurring. Unlike the severe acute respiratory syndrome (SARS) epidemic, which rapidly disappeared in less than one year, MERS has persisted for over three years. More than 1,600 cases of MERS have been reported worldwide, and the disease carries a worryingly high fatality rate of >30%. A total of 182 MERS-CoV genomes have been sequenced, including 94 from humans and 88 from dromedary camels. The 182 genomes all share >99% identity, indicating minimal variation among MERS-CoV genomes. MERS-CoV is a lineage C Betacoronavirus (sCoV). MERS-CoV genomes can be roughly divided into two clades: clade A, which contains only a few strains, and clade B, to which most strains belong. In contrast to ORF1ab and structural proteins, the putative proteins encoded by ORF3, ORF4a, ORF4b, ORF5 and ORF8b in the MERS-CoV genome do not share homology with any known host or virus protein, other than those of its closely related lineage C sCoVs. Human and dromedary viral genomes have intermingled, indicating that multiple camel-to-human transmission events have occurred. The multiple origins of MERS-CoV suggest that the virus has been resident in dromedaries for many years. This is consistent with the detection of anti-MERS-CoV antibodies in dromedary camels as early as the 1980s.