Cholera

Cholera is a water borne disease caused by Vibrio cholerae.
The main symptom of Cholera is diarrhoea. This is caused by movement of electrolytes from the epithelial cells into the lumen of the gut, subsequently followed by water.
The Cholera toxin increases the activity of adenylyl cyclase. This results in greater production of cyclic AMP (cAMP) and cAMP activates Protein Kinase A (PKA) in CFTR cells.
In the CFTR cell PKA leads to the opening of chloride channels and chloride ions move from the cell into the lumen. Chloride ions are negatively charged and create an electrochemical gradient.
Positively charged sodium ions also move into the lumen via ENaC in the apical membrane in order to balance this electrochemical gradient. Cholera toxin increases the expression of ENaC in the apical surface of the membrane and consequently sodium absorption is intensified. 
The movement of sodium increases the osmolarity in the lumen and water then moves from the intracellular fluid into the extracellular fluid resulting in diarrhoea. Oral rehydration therapy should be commenced promptly to prevent dehydration which if untreated could be fatal.