Cholera

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How the cholera bacterium causes disease

Symptoms:

Diarrhoea

Dehydration

(Some people show few, if any, symptoms- only acting as carriers (spreading the disease unwittingly)

Transmission:

By the ingestion of water (or more rarely food) that has been contaminated with faecal material containing this pathogen.

Once ingested symptoms are caused by the following ways...

Almost all Vibrio cholerae bacteria ingested by humans killed by acidic conditions in stomach. However, few may survive (especially if pH is about 4.5)

When surviving bacteria reach small intestine they use flagella to propel themselves through mucus lining of intestinal wall.

Produce a toxic protein which has 2 parts. One part binds to specific carbohydrate receptor on CSM (the epithelial cells of the small intestine are the only ones to have these specific receptors- explaining why cholera only affects this region of the body.) 2nd part enters epithelial cells causing ion channels of CSM to open so chloride ions (normally contained within cells) flood into lumen of intestine.

Loss of chloride ions in cells raises water potential, while increase of ions in lumen lowers water potential. Water therefore flows from cells into lumen.

Loss of ions from cells establishes conc. gradient. Ions therefore move by diffusion into cells from surrounding tissues, including blood. This, in turn, establishes water potential gradient causing water to move by osmosis from blood/other tissues into intestine.

It is the loss of water from blood/other tissues which cause symptoms of cholera.

Treatment

Cholera is treated by restoring water and ions that have been lost by the use of oral rehydration therapy (drink containing ions and sugars dissolved in water.) E.g. sodium ions included to increase glucose absorption - sodium and glucose co-transported into epithelium cells of intestine.

Transmission of cholera

Contamination of the water can arise because..

Drinking water not properly purified

Untreated sewage leaks into water courses

Food contaminated by people who prepare/serve it

Organisms (e.g shellfish) which feed on untreated sewage then released into rivers or the sea.

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