Genetic drift in camel and dromedary camel MERS-CoV was delayed
By far, most of MERS-CoV outbreak occurred in Saudi Arabia and almost all human infections were linked directly or indirectly to Arabian Peninsula. Camels and dromedary camels are supposed to be sources of human zoonotic infection of MERS-CoV since the serum of camels contain specific antibodies against MERS-CoV spike protein (13, 14). We also analyzed 74 complete genome sequences of camel MERS-CoV and 132 dromedary camel MERS-CoV in Saudi Arabia and United Arab Emirates, respectively. Both countries are located in Arabian Peninsula. Only U—-U type virus was detected in 2013 in Saudi Arabia (Figure 2C) or in 2014 in United Arab Emirates (Figure 2D). C—-U type virus then emerged and became dominant in Saudi Arabia in 2014. One year later, this type virus emerged in United Arab Emirates. While the camel MERS-CoV displayed a genetic drift from U—-U to C—-U, the timeframe between human and camel viruses is not in consistence. Noticeably, in 2015, almost 43% of human MERS-CoVs were C—-C type virus in Saudi Arabia, but this type virus was never ever detected in camels in Saudi Arabia (Figure 2C) or United Arab Emirates (Figure 2D) at the same period. In contrast to SARS-CoV-1 and -2, direct human-to-human transmission of MERS-CoV seems to be limited (10). While the main known exposures to MERS-CoV are health care-associated infections or contact with camels (Drosten et al. 2015), the source of infection for most primary human cases are still not known (Fanoy et al. 2014). Camels are believed to be the natural reservoir for human infection (13, 14). However, this notion may not be supported by the results shown here. While we can not exclude the species-cross transmission between human and camels, the results in this report suggest that human infection may have independent unknown source of infection.