Researchers from Ireland, China, France, Germany and the United States, examined the past 10,000 years of global plague disease events. Their collaborative research
traced the roots to somewhere in or around present-day China.
The plague spread over various historical trade routes in the 15th century. Chinese admiral and explorer Zheng He is likely to have carried it to Central Africa during his travels. The legendary Silk Road
too may have provided a pathway for disease as it did for trade between China and the Western world.
The Black Death
, one of the deadliest pandemics in human history, is estimated to have killed 30-60 percent of Europe's population, reducing the world's population from an estimated 450 million to between 350 and 375 million in 1400.
While plague today is less of a threat to human beings than during other periods in history, such as the Middle Ages, the current plague research can be applied to ongoing health threats around the world. While the scary pandemics have been relegated to medieval history, the disease has not been eradicated totally. The bacterium remains ecologically established in animal populations around the world, and has resurfaced in Africa and Madagascar.
In fact, the last plague pandemic of the late 1800s still persists today in wild rodents throughout western United States. Plague entered the US sometime in the late 19th and early 20th century through multiple port cities by infected ship-borne rats. The team carried out DNA tests and found that the original plague strains that infected the US had their origin in Asia and likely made their way to California via Hawaii.
The findings regarding the plague pathogen, Yersinia pestis, will be published in an upcoming issue of the international science journal, Nature Genetics
The team was able to identify unique mutations in country-specific plague lineages. The scientists worked out a strategy of decentralised experiments with the team members working with one or several of 17 complete plague whole genome sequences. They subsequently electronically combined the data, and identified hundreds of variable sites in the DNA while assembling one of the largest dispersed global collections of plague isolates. Next they reconstructed the spread of plague pandemics and calculated the age of different waves of outbreak.