But with SARS1 and MERS they were able to find the virus that jumped to humans in civets and camels within months by tracing back mutations as the virus adapted to humans. When viruses are circulating in humans they don't just suddenly stop once it spills over into humans since the virus is already well adapted to their own species. You'd think after 3 + years of testing and searching we'd find a closely related virus circulating in animals that is not the result of humans -> animals. The fact that there has not been a follow up outbreak, and the missing trail of mutations as the virus adapts towards humans really sticks out.