It is possible that we'll never know. However, remember that we also recently have SARS, MERS, EBOLA, etc. This isn't some isolated event. We've made the world small, there is no where too remote. Some animal from the remotest village on earth can be sold on the street in NYC in two days. Who knows what ancient pathogens are being re-released from the permafrost? I fear this is the beginning of mother earth fighting back, not the end.