Err, that's explicitly covered in the last paragraph; I've included a bit more for context:
[...] Moreover, their results challenge the long-standing, but poorly substantiated view that Yersinia pestis must have had a permanent wildlife reservoir in Europe, such as the urban black rat. Instead, new strains of the disease may have been frequently imported from Asia.
Nevertheless, an ultimate confirmation of this hypothesis depends on the availability of appropriate genetic material of ancient plague victims not only from different periods throughout time but also from different parts of Eurasia. The advent of aDNA techniques and international research collaboration across disciplinary boundaries will most likely be able to shed new light on this fascinating topic at the interface of human history and environmental variability.
We've already reconstructed Yersinia pestis strains from victims of the Black Death and the 6th Century Plague of Justinian....
[...] Moreover, their results challenge the long-standing, but poorly substantiated view that Yersinia pestis must have had a permanent wildlife reservoir in Europe, such as the urban black rat. Instead, new strains of the disease may have been frequently imported from Asia.
Nevertheless, an ultimate confirmation of this hypothesis depends on the availability of appropriate genetic material of ancient plague victims not only from different periods throughout time but also from different parts of Eurasia. The advent of aDNA techniques and international research collaboration across disciplinary boundaries will most likely be able to shed new light on this fascinating topic at the interface of human history and environmental variability.
We've already reconstructed Yersinia pestis strains from victims of the Black Death and the 6th Century Plague of Justinian....