The fateful arrival of plague bacteria in the Mediterranean during the mid 14^th century sparked one of the deadliest pandemics of all of human history, dubbed the Black Death. The pandemic killed up to 50 percent of the European population as it rapidly spread. In the following four centuries, plague outbreaks continued to flare up in pockets across the continent. And in the late 19^th century, the plague took hold in the East, sparking the next historic pandemic in China.

For decades, researchers have tried to retrace the plague’s steps. Some have speculated that multiple strains of the bacteria creeped onto the continent—most likely from Asia—igniting new bouts of disease with sometimes different sets of symptoms. The hypothesis follows with the current state of the plague in China, where there are multiple lineages floating around. But a new study casts doubt on the idea.

Fresh genetic sequencing data of plague bacteria from victims in Spain, Germany, and Russia suggest that a single wave of the deadly microbes sparked the Black Death as well as the subsequent outbreaks that flared for centuries in Europe and the 19^th century pandemic in China. This single wave also gave rise to plague strains behind some modern outbreaks. The study is the first to make a genetic link between the Black Death and modern plague, the authors report in Cell Host & Microbe.