The Gangetic delta is a century-old cholera endemic belt where the role of riverine-estuarine ecosystem in cholera transmission has never been elucidated. Seasonality, distribution, and abundance of environmental Vibrio cholerae O1/O139 and vibriophage in Hooghly riverine-estuarine environment and their correlation with cholera incidence pattern in West Bengal, India, have been analyzed for the first time across summer, monsoon, and winter months. A total of 146 water samples collected from two sites of the Hooghly River (Howrah and Diamond Harbour) were analyzed physicochemically along with cultivable Vibrio count (CVC), V. cholerae O1/O139, and vibriophages. V. cholerae O1 was detected in 56 (38.3%) samples, while 66 (45.2%) were positive for V. cholerae O1 phages. Flood tide, water temperature (31 ± 1.6 °C), and turbidity (≥250 nephelometric turbidity unit (NTU)) significantly stimulated V. cholerae and vibriophage abundance in riverine ecosystem. Solitary existence of V. cholerae O1 and phages (p < 0.0001) in aquatic environment divulges the dominance of either of the entity (V. cholerae O1 or V. cholerae O1 Φ) on the other. Significant association (p < 0.05) between Kolkata cholera cases and V. cholerae O1 in aquatic environment implies the role of riverine-estuarine ecosystem in cholera transmission. A "biomonitoring tool" of physicochemical stimulants, tidal, and climatic variants has been proposed collating V. cholerae and phage dynamics that can forewarn any impending cholera outbreak.
Diarrheal disease remains an unsolved problem in developing countries. The emergence of new etiological agents (non-cholera vibrios) is a major cause of concern for health planners. We attempted to unveil the seasonal dynamics of entero-pathogenic Vibrios in Gangetic riverine-estuarine ecosystem. 120 surface water samples were collected for a period of one year from 3 sampling sites on the Hooghly river. Five enteropathogenic Vibrio species, V. cholerae (35%), V. parahaemolyticus (22.5%), V. mimicus (19.1%), V. alginolyticus (15.8%) and V. vulnificus (11.6%), were present in the water samples. The vibriophages, V. vulnificus ɸ (17.5%), V. alginolyticus ɸ (17.5%), V. parahaemolyticus ɸ (10%), V. cholerae non-O1/O139 ɸ (26.6%) and V. mimicus ɸ (9.1%), were also detected in these samples. The highest number of Vibrios were noted in the monsoon (20–34°C), and to a lesser extent, in the summer (24–36°C) seasons. Samples positive for phages for any of the identified Vibrio species were mostly devoid of that particular bacterial organism and vice versa. The detection of toxin genes and resistance to β-lactam antibiotics in some environmental enteropathogenic Vibrio species in the aquatic niches is a significant outcome. This finding is instrumental in the south Bengal diarrhoeal incidence.
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