ABSTRACT
Since the causative agent of plague was first identified as a Gram-negative bacterium by Alexander Yersin in 1894, our understanding of the epidemiology, genetics and evolution of Yersinia pestis has come a long way. Y. pestis is thought to have been responsible for three human pandemics; the Justinian plague (6th to 8th centuries), The Black Death (14th to 19th centuries) and the current pandemic or Modern plague (19th century to present day). The Black Death alone is estimated to have claimed one third of the European population. A wealth of paintings and detailed historical writings have recorded the dramatic impact that plague has had on the development of modern civilization. This historical data combined with phenotypic analysis of strains isolated from foci known to have been affected in different pandemics has allowed isolates of Y. pestis to be split into three biovars: Biovar Antiqua is thought to be representative of strains that were responsible for the Justinian plague, similarly biovar Medievalis is thought to be representative of those responsible for The Black Death and biovar Orientalis is responsible for the current pandemic (Devignat, 1951).
