Bordetella pertussis causes whooping cough (pertussis) in humans. Despite high routine vaccination coverage, whooping cough remains a public health problem and is reemerging in many countries, since the 1990s. While a plethora of candidate explanations for this resurgence remain hotly debated, two main ideas suggested focus on vaccine driven pathogen adaptation and on the change from whole cell to acellular vaccines. Pathogen adaptation is proposed to occur through antigenic divergence between vaccine and circulating strains as well as surfacing of strains with increased pertussis toxin production. We employ generalized linear models within a Bayesian coalescent framework to formally tests drivers of evolution in Bordetella pertussis populations, and the role of allele shifts in the resurgence of pertussis. We use long-term clinical isolates, incidence and demographic data for the Netherlands, between 1949 and 2012.
Results/Conclusions
We document significant shifts in B. pertussis population that could suggest pathogen adaptation. There is evidence for loss of diversity, punctuated by episodes of clonal expansion in the population. The negative association between gene diversity and incidence and an increase in mean age of infection validates our hypothesis that the resurgence is associated with the expansion of specific strains and not due to an increase in transmission. More specifically, our model reveals that acellular vaccine cannot be contributing to the pertussis resurgence. This work provides insight into ways in which pathogens may adapt under several driving forces of selection and suggests ways to improve pertussis control.