THE EXAMPLE OF YERSINIA PESTIS

Plague is a disease that has shaped the social, genetic and industrial makeup of many populations and especially those in Europe. The pandemic of disease which had the greatest impact on Europe occurred during the 14th to 16th centuries and is usually referred to as the ‘Black Death’ (Perry & Fetherston, 1997). During this pandemic it is estimated that 30% of the population of Europe died. The Justinian plague occurred in AD 541 to 544, originally in Egypt but then spreading through the Mediterranean and Middle East eventually to involve most of the known world (Perry & Fetherston, 1997). The third pandemic of plague originated in China in the 1850s but the impact of this pandemic was minimal in Europe. However, during the peak of the outbreak in India at the end of the 19th century, the disease killed a million individuals a year (Perry & Fetherston, 1997). Nowadays, the 2000–3000 cases of plague which are reported to the World Health Organization each year (Anonymous, 2000) are considered to be the vestigial remnants of the third plague pandemic.

The aetiological agent of plague is Yersinia pestis, one of three human-pathogenic Yersinia species. The human pathogenic Yersinia are closely related but cause very different diseases (Brubaker, 1991). Both Yersinia enterocolitica and Yersinia pseudotuberculosis cause relatively mild, self-limiting infections of the gastrointestinal tract, whereas Y. pestis causes an acute systemic infection which is often fatal.