It’s from a long period of raising pigs and chickens close to people in ultra high density agriculture with little sanitation and using the wastes of the former to feed plants and pond/paddy fish. More likely than not, the rural folk there weren’t or aren’t majorly affected by the cycle. It probably started “out breaking” there when outsiders and city folk started mingling or conflict pushed movement.
That’s the story we’ve been sold. I recall it from my schooling in the 80s.
True?