My understanding (not an expert - just saw the articles in 2016-2017) is that it might have been pre-existing but no one was looking because human-human transmi

My understanding (not an expert - just saw the articles in 2016-2017) is that it might have been pre-existing but no one was looking because human-human transmission was overwhelmingly dominant. But I had he date wrong - apparently it was first observed in 2012, but only became a significant vector in 2016 (presumably as humans stopped being such accessible hosts).