BUBONIC PLAGUE - A MOLECULAR-GENETIC CASE-HISTORY OF THE EMERGENCE OFAN INFECTIOUS-DISEASE

Yersinia pestis, the bacterial agent of bubonic plague, is transmitted primarily by fleas and has been responsible for devastating epidemics throughout history. Y. pseudotuberculosis is a food-and water-borne p athogen that causes a much more benign enteric disease in humans, Desp ite these profoundly different pathogenesis strategies, the two bacter ia are very closely related phylogenetically. Thus, identifying the sp ecific genetic differences between them should provide an instructive case study in the evolution of microbial pathogenicity. Some key patho genesis-related genes of Y. pestis and Y. pseudotuberculosis that have been described to date are compared in this review. Factors that pote ntiate plague transmission as well as disease are discussed, since dep endence on the blood-sucking flea for transmission likely fueled the s election of virulent Y. pestis strains able to produce a high-density bacteremia, Retracing the evolutionary steps between these two Yersini a species may ultimately furnish a historical model for the sudden eme rgence of new human disease agents.