Molecular Evolution of MERS Coronavirus: Dromedaries as a Recent Intermediate Host or Long-Time Animal Reservoir?

Lau, Susanna K. P.; Wong, Antonio C. P.; Lau, Terrence C. K.; Woo, Patrick C. Y.

Among all known CoVs, the largest numbers of complete/near-complete genomes are available for SARS-CoV and MERS-CoV, of which >300 and >200 genomes, respectively, are available for analysis. Such large number of genomes has given us a good opportunity to improve our understanding on the origin and evolution of the corresponding viruses. In contrast to the major SARS outbreak in 2003 which is of monophyletic origin, MERS-CoVs circulating in human and camels since 2012 originated from multiple sources in the Middle East and North Africa. For example, strains from a single country such as the UAE are present in lineages A2, B1, 3, 4, and 5, and strains from Jordan are also present in lineages A1, B4, and B5. This indicated that different MERS-CoV strains have resided in dromedaries in different countries with sporadic transmission to humans, sometimes causing fatal diseases. Overall, some minor recombination events between different sublineages (between B5 and B3, and between B3 and B4) might have occurred (Figures 5 and 6 ), but it seems that none of these events has resulted in significant changes in the genome. This is in contrast to some CoVs such as human CoV HKU1, human CoV OC43, or canine CoVs where recombination events are responsible for the generation of novel genotypes [16] [17] [18] .