Genetic tracking and characterization of naturally occurring Vibrio cholerae causing endemic cholera in Bangladesh

Cholera, a scourge, remains one of the major causes of morbidity and mortality world-wide. The global burden of cholera is estimated to be about 3-5 million cases each year with an estimated deaths of 100,000 to 120,000, majority occurring in the developing countries of Asia and Africa. The causative agent of cholera, Vibrio cholerae, is a genetically versatile bacterial species for which more than 200 serogroups have been identified and for which significant lateral transfer of genes has been demonstrated. Pandemic cholera is generally caused by toxigenic strains of V. cholerae serogroups O1 and O139. V. cholerae O1 has been divided into two biotypes, classical (CL) and El Tor (ET), differing primarily in phenotypic traits and distinct signature genome sequences. Of seven cholera pandemics recorded since 1817, the sixth and presumably the earlier pandemics have been caused by CL biotype, which was replaced in the 1980s by ET biotype initiating the currently ongoing seventh cholera pandemic. The Ganges Delta of the Bay of Bengal has been the traditional home where cholera is endemic for centuries. Although V. cholerae has been an integral part of the bacterial community sharing niche in the estuarine ecosystem of Bay of Bengal, a little is known about the aquatic life cycle of V. cholerae, particularly how a pandemic pathogen emerges from the naturally occurring benign population of this historic ecosystem.