> My understanding is that it took a while before the (natural) emergence of SARS and MERS was understood, and so for COVID most probably. The proximal host is

> My understanding is that it took a while before the (natural) emergence of SARS and MERS was understood, and so for COVID most probably. The proximal host is the animal that transmitted the virus to humans. That host was identified for SARS-1 (civet cats) and MERS (camels) within about a year. For example, here's an article from 2003: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1140695/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1140695/ The reservoir host is the animal in which most of the virus's genome evolved. That host (bats for both) took much longer to identify, through Dr. Shi's work at the WIV. Since SARS-CoV-2 is very similar to SARS-1, we knew its reservoir host (bats) as soon as it was sequenced. We still don't know its proximal host. The proximal host is the critical question in establishing natural zoonotic origin--no one disputes that SARS-CoV-2 evolved mostly in bats, just whether its path into humans involved a research accident.