Pathogenicity and virulence of Bordetella pertussis and its adaptation to its strictly human host

The highly contagious whooping cough agent Bordetella pertussis has evolved as a human-restricted pathogen from a progenitor which also gave rise to Bordetella parapertussis and Bordetella bronchiseptica. While the latter colonizes a broad range of mammals and is able to survive in the environment, B. pertussis has lost its ability to survive outside its host through massive genome decay. Instead, it has become a highly successful human pathogen by the acquisition of tightly regulated virulence factors and evolutionary adaptation of its metabolism to its particular niche. By the deployment of an arsenal of highly sophisticated virulence factors it overcomes many of the innate immune defenses. It also interferes with vaccine-induced adaptive immunity by various mechanisms. Here, we review data from in vitro, human and animal models to illustrate the mechanisms of adaptation to the human respiratory tract and provide evidence of ongoing evolutionary adaptation as a highly successful human pathogen.