Evidence supporting a zoonotic origin of SARS-CoV-2
Coronaviruses have long been known to present pandemic risks. SARS-CoV-2 is the ninth documented coronavirus that infects humans and the seventh identified in the last 20 years1,2. All previous human coronaviruses have zoonotic origins, as have the vast majority of human viruses. The emergence of SARS-CoV-2 bears several signatures of these prior zoonotic events. It displays clear similarities to SARS-CoV that spilled over into humans in Foshan, Guangdong province, China in November 2002, and again in Guangzhou, Guangdong province in 20033 . Both these SARS-CoV emergence events were associated with markets selling live animals and involved species, particularly civets and raccoon dogs4 , that were also sold live in Wuhan markets in 20195 and are known to be susceptible to SARS-CoV-2 infection6 . Animal traders working in 2003, without a SARS diagnosis, were documented to have high levels of IgG to SARS-CoV (13% overall and >50% for traders specializing in civets7 ). Subsequent serological surveys found ~3% positivity rates to SARS-CoV related (SARSr-CoV) viruses in residents of Yunnan province living close to bat caves8 , demonstrating regular exposure in rural locations. The closest known relatives to both SARS-CoV and SARS-CoV-2 are viruses from bats in Yunnan, although animals from this province have been preferentially sampled. For both SARS CoV and SARS-CoV-2, there is a considerable geographic gap between Yunnan and the location of the first human cases, highlighting the difficulty in identifying the exact pathway of virus emergence and the importance of sampling beyond Yunnan.
