The microbe responsible for plague evolved in or around China more than 2,600 years ago and spread around the globe in the following millennia, according to the most comprehensive genetic study to map out the family tree of the bacterium known as Yersinia pestis.
Y. pestis' pedigree is not only ancient, it is dramatic. Plague has been blamed for decimating societies, notoriously wiping out roughly a third of Europe's population during the Black Death in the mid-14th century.
This pestilence is still alive and well; the youngest strains evolved more than 210 years ago, by the researchers' calculations, and have spread to the United States, South America, Europe, continental Africa, Madagascar, Turkey and Southeast Asia.
Bubonic plague, the most common form, first infects rats or other small animals, and it is spread by the fleas that bite them. Infected humans suffer from swollen lymph glands, called buboes, caused by the plague bacteria, as well as flu-like symptoms. Left untreated, plague can kill 60 percent of its victims, according to the World Health Organization.
This bacterial family tree can shed light on both the past and future of plague, said study co-author Mark Eppinger, a researcher at the Institute for Genomic Sciences at the University of Maryland School of Medicine. While it reflects the spread of plague in ancient times, it can also provide a reference for future outbreaks by helping to identify their origin, he said.