The authors in this new study say the plague evolved around the area of China over 2000 years ago and spread globally several times as deadly pandemics. They compared 17 complete plague genome sequences as well as 933 variable DNA sites on a unique worldwide collection of bacterial strains (plague isolates), allowing them to follow pandemics that took place in history around the world, and to work out the age of different waves of them.
In order to prevent bioterrorism, access to Yersinia pestis - the bacterium known to be the cause of the plagues - is seriously restricted; therefore, assembling a comprehensive collection of them is impossible. An international team of scientists from the UK, USA, Ireland, Germany, Madagascar, China and France had to collaborate for a decentralized analysis of DNA samples.Melinda Meade and Robert Earickson, in their book on Medical Geography, remind us that the childhood game of ring around the rosy is a somewhat creepy relic of the old days of the plague in Europe. "Ring around the rosy" represents the rash around the flea bite; "a pocket full of posey" is a reminder that posey (a flower) was carried by people to prevent the spread of the disease (ineffectually, of course!); "ashes, ashes" or "achoo, achoo" (in Germany) referring either to the sign of the cross representing a sick person's home or to the sneeze that signaled the onset of the disease; and "we all fall down" meaning, of course, that we all die.