I agree with others. I suspect that pretty much everything that attacks humans today has been ‘Lurkin for many millions of years, but cannot break out unless the conditions are right, with the two key conditions being population density and sanitation. One in a while one of these microbes pops up, takes out some people, but don’t have the capability to go widespread. But if the populace is already weakened, and living tightly together, watch out.
Most of the really bad ones (Ebola, Marburg and likely AIDS) seem to have originated near Lake Victoria, which is in Kenya, Uganda, and Tanzania. The alpha and omega of mankind.