Identification of the host reservoir of SARS-CoV-2 and determining when it spilled over into humans

1Since the emergence of SARS-CoV-2 in Wuhan in 2019 its host reservoir has not been established. Phylogenetic analysis was performed on whole genome sequences (WGS) of 71 coronaviruses and a Breda virus. A subset comprising two SARS-CoV-2 Wuhan viruses and 8 of the most closely related coronavirus sequences were used for host reservoir analysis using Bayesian Evolutionary Analysis Sampling Trees (BEAST). Within these genomes, 20 core genome fragments were combined into 2 groups each with similar clock rates (5.9x10-3 and 1.1x10-3 subs/site/year). Pooling the results from these fragment groups yielded a most recent common ancestor (MRCA) shared between SARS-COV-2 and the bat isolate RaTG13 around 2007 (95% HPD: 2003, 2011). Further, the host of the MRCA was most likely a bat (probability 0.64 - 0.87). Hence, the spillover into humans must have occurred at some point between 2007 and 2019 and bats may have been the most likely host reservoir.