This applies to diseases which are importantly but not always mortal. And very contagious. Like coronavirus Very contagious diseases which are rarely mortal ne

This applies to diseases which are importantly but not always mortal. And very contagious. Like coronavirus Very contagious diseases which are rarely mortal never go away. Like chicken pox Not very contagious diseases which are always mortal don't spread far away. Like ebola and maybe the original pest. They require a reservoir lest they vanish forever. Very contagious and always mortal diseases are self limited, they kill whole populations. One of the downsides of a global community is that almost the whole humanity is one population. Self sufficient populations are found in the north pole. And in some island east of India called "Sentry island". I hope there are more