B.S. Drasar & B.D. Forrest 
Cholera and the Ecology of Vibrio cholerae [PDF ebook] 

Only in recent years has it been revealed that V. cholerae is a normal inhabitant of esturine and riverine waters. This means that even if the disease can be eliminated from human population by vaccines etc. the vibrio will continue to survive independently in the environment. It is likely that the environment is the source of epidemic strains. This is the first book to focus on the implication of these discoveries.