A Mathematical Model for the Rise in Pertussis

The incidence of whooping cough, caused by the bacterium Bordetella pertussis, is currently on the rise. In 2012, the United States saw the highest levels of incidence since 1955. Current research shows that the bacteria may have evolved to evade vaccine-derived immunity. These new strains lack pertactin, a cell-surface protein of the bacteria that is a main component of the vaccine. The lack of pertactin results in a lowered rate of transmission. The evolving bacteria must balance the loss of virulence with an increased ability to evade acquired immunity. Compartmental modelling can be used to determine the evolutionary stable strategy of optimal virulence, where the pathogen can maximize evasion of vaccine-acquired immunity while minimizing loss of infectiveness