Vibrio cholerae O139 genomes provide a clue to why it may have failed to usher in the eighth cholera pandemic

Cholera is a life-threatening infectious disease that remains an important public health issue in several low and middle-income countries. In 1992, a newly identified O139 Vibrio cholerae temporarily displaced the O1 serogroup. No study has been able to answer why the potential eighth cholera pandemic (8CP) causing V. cholerae O139 emerged so successfully and then died out. We conducted a genomic study, including 330 O139 isolates, covering emergence of the serogroup in 1992 through to 2015. We noted two key genomic evolutionary changes that may have been responsible for the disappearance of genetically distinct but temporally overlapping waves (A-C) of O139. Firstly, as the waves progressed, a switch from a homogenous toxin genotype in wave-A to heterogeneous genotypes. Secondly, a gradual loss of antimicrobial resistance (AMR) with the progression of waves. We hypothesize that these two changes contributed to the eventual epidemiological decline of O139. The O139 Vibrio cholerae serogroup emerged in the 1990s and spread rapidly but did not become globally dominant. Here, the authors describe the genomic epidemiology of this strain and identify changes in virulence and antimicrobial resistance characteristics that they hypothesise may have contributed to its decline.