Although first detected in December 2019, COVID-19 was inferred to be present in Hubei province, China, for about a month before (1). Where did this new human disease come from?
To understand the origin of the COVID-19 pandemic, it is necessary to go back to 2002. At that time a novel respiratory coronavirus appeared in Foshan, Guangdong province, China, and spread to 29 countries (2). Altogether ∼8000 people were infected with severe acute respiratory syndrome coronavirus (SARS-CoV) before public health measures controlled its spread in 2003.
The zoonotic [animal] origin of SARS-CoV was subsequently linked to live animals available at markets. Further sporadic spill-over events of SARS-CoV from animals took place in Guangzhou, Guangdong, and some researchers working with cultured virus were infected in laboratory accidents (3), but ultimately SARS-CoV was removed from the human population. Trading of susceptible host animals is an important common theme in the emergence of SARS and COVID-19.