Plague was around for millennia before epidemics took hold – and the way people lived might be what protected them

One of civilization’s most prolific killers shadowed humans for thousands of years without their knowledge. The bacteria Yersinia pestis, which causes the plague, is thought to be responsible for up to 200 million deaths across human history — more than twice the casualties of World War II. ....
http://theconversation.com/plague-was-around-for-millennia-before-epidemics-took-hold-and-the-way-people-lived-might-be-what-protected-them-120316