It is thought that this nursery rhyme has origins from plague. “Ring” refers to an early clinical sign that appears on the skin (perhaps the ulcer that commonly appears around a flea bite wound infected with Y. pestis ); “a pocket full of posies” refers to the use of flower petals as a means of warding off the stench and infection of a plague victim; “ashes, ashes” refers to dust to dust; and “all fall down” refers to victims who were falling down dead.
In addition to the common Yersinia virulence plasmid pCD~70-kb ,Y.pestis harbours 2 unique plasmids regulting its transmission:the murine toxin (pMT1 ~100-kb) and plasminogen activator/ ‘pesticin’ (pPCP ~9.6kb) plamids
Plasmids carry ‘molecular fingerprints’ left behind during evolution and account for emergence of Y.Pestis
The DNA relationship between Y. pestis and Y.
pseudotuberculosis chromosomes is greater than eighty percent as measured by DNA::DNA hybridization analysis