The first human cases of COVID-19 were identified in Wuhan City, China in December 2019. At this stage, it is not possible to determine precisely how humans in China were initially infected with SARS-CoV-2.
However, SARS-CoV, the virus which caused the SARS outbreak in 2003, jumped from an animal reservoir (civet cats, a farmed wild animal) to humans and then spread between humans. In a similar way, it is thought that SARS-CoV-2 jumped the species barrier and initially infected humans, but more likely through an intermediate host, that is another animal species more likely to be handled by humans - this could be a domestic animal, a wild animal, or a domesticated wild animal and, as of yet, has not been identified.
Until the source of this virus is identified and controlled, there is a risk of reintroduction of the virus in the human population and the risk of new outbreaks like the ones we are currently experiencing.