Role of estuarine biogeochemistry on abundance and types of Vibrio cholerae in West Bengal: seasonality and relation with cholera incidence

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The Ganges delta embraces the likely largest mangroves (Sunderbans) worldwide. Yet, the dynamics of this aquatic ecosystem with high organic matter input and strong, recurrent floods are poorly understood, particularly the seasonal variation and links of water biogeochemistry and microbiology. Vibrio cholerae is a natural inhabitant of these waters. Although this ecosystem has been related since ancient times to endemic cholera, most evidence relating disease incidence to aquatic ecosystems has been mostly obtained from inland ponds or ocean parameters. There are no systematic studies establishing causal links between the yearly cycles of organic, inorganic nutrients and physico-chemical parameters in West Bengal estuaries and the seasonal dynamics of V. cholerae, a main objective of this project. Further, specific hypotheses to be investigated are:(a) Chitinaceous micro-detritus rather than Zooplankton are a main V. cholera reservoir(b) Even at environmental concentrations, higher contents of chitin, salt, nutrients andphages favor short-term emergence of new variants of pathogenic aquatic V. cholerae.(c) There are niches in Sunderbans hosting specific V. cholerae, including pathogenicserogroups ( nonmar or hybrid).The seasonality of cultivable or dormant forms, 01, 0139, non-01 and non-0139 serotypes will help understand epidemic and interepidemic periodicity. The study will reveal if specific V. cholerae types are more resistant to estuarine gradients and how sediment resuspension by cyclones influences V. cholerae diversity and abundance in the water column. These data will be related to seasonal cholera incidence patterns.