Page "Yersinia pestis" Paragraph 7

Three biovars of Y. pestis were originally thought to correspond to one of the historical pandemics of bubonic plague.

Biovar Antiqua is thought to correspond to the Plague of Justinian ; it is not known whether this biovar also corresponds to earlier or smaller epidemics of bubonic plague, or whether these were even truly bubonic plague.

Biovar Mediaevalis was formerly thought to correspond to the Black Death, while Biovar Orientalis was thought to correspond to the Third Pandemic and the majority of modern outbreaks of plague.

However, calculations of Y pestiss evolutionary age, found using the number of synonymous single nucleotide polymorphisms ( SNPs ) in conjunction with molecular clock rates, date the emergence of the biovars prior to any of the historical epidemics due to the length of time needed to accumulate such mutations.

Additional evidence against this hypothesis includes the fact that Mediaevalis is likely too young to have produced the Black Death due to its recent divergence from Orientalis.