3.10 Cholera

3.10 Cholera

1. Caused by curved, rod-shaped bacterium called Vibrio cholerae

2. Symptoms

   • Diarrhoea
   • Dehydration
   • Some individuals act as carriers
     • Show few, if any, symptoms but still have the disease

3. Transmission

   • Ingestion of water or food contaminated with faecal material containing pathogen
     • Water not properly purified
     • Untreated sewage leaks
     • Preparing/serving food from people with faecal contamination of hands
     • Organisms that have fed on untreated sewage released into rivers/sea
     • Lack of clean water; poor sanitation; lack of basic house facilities

4. Process

   • Most Vibrio cholerae bacteria killed by acidic conditions in stomach
     • Remaining bacteria continue to small intestine
       • Bacteria use flagella to enter through mucus lining of epithelial wall
         • Bacteria produce toxic protein
           • Toxic part of protein enters epithelial cells
             • Ion channels of cell-surface membrane open
               • Chloride ions within epithelial cells flood into intestinal lumen
                 • Loss of chloride ions in epithelial cells increases water potential of epithelial cells
                   • Increase of chloride ions in lumen lowers water potential of lumen
                     • By osmosis, water moves down concentration gradient from epithelial cells into lumen
                       • Loss of ions in epithelial cells = concentration gradient of ions
                         • By diffusion, ions move from surrounding tissues (inc. blood) into epithelial cells
                           • Also establishes water potential gradient = by osmosis, water moves from blood and tissues into intestine
                             • Loss of water from blood and tissues into intestine causes symptoms of cholera (diarrhoea, dehydration)