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Cholera is an infectious disease caused by Vibrio cholerae, which is a major cause of death in areas of the world where a proper infrastructure for good sanitation doesn’t exist. Bacteria are ingested by consuming contaminated water and food. The water becomes contaminated when a person with the disease (which causes severe diarrhoea) produces the faeces which then carry the bacteria in the water supply.


As all bacteria, Vibrio cholarae is a prokaryotic organism. Prokaryotes do not have a nucleus like eukaryotes do. Their DNA is not membrane-bound, just free in the cytoplasm.



The features of prokaryotic cells you must learn are:


-Cell wall

-Cell-surface membrane

-Capsule (protective layer)

-Circular DNA (as all DNA, it stores the genetic information)

-Flagella (used for movement – think sperm cells)

-Plasmid (small loop of DNA which can be copied and passed on to other bacteria by conjugation)


The cholera bacteria cause severe diarrhoea by producing a toxin which binds to receptors in the small intestine; this in turn activates cyclic AMP (which is a messenger molecule) which results in chloride pumps staying open all the time. Under normal conditions, these pumps would open and close accordingly to adjust water content in the small intestine. In cholera however, chloride ions are free to rush out into the lumen (“empty” space), as well as other ions such as sodium. This causes the water potential in the lumen to decrease (so water moves in by osmosis from cells lining the small intestine into the lumen), which results in a high amount of water being lost from the body.


All is not lost though, because the treatment for cholera is indeed easily available and relatively cheap. This is called oral rehydration therapy with Oral Rehydration Solutions (ORS). When the body loses many essential ions and water by severe diarrhoea, the solution (pun intended) is an oral rehydration solution which throws much needed water and nutrients e.g. glucose (for energy), calcium, chloride, sodium and potassium, back into the patient.


ORS = 1L water + 8 teaspoonfuls sugar + 1 teaspoonful salt

This is a basic DIY recipe, but pharmaceutical companies work on better recipes.


You should be aware of the ethical aspects of using ORS when there are experimental trials on humans. They must do it voluntarilyconsent to it, have it carried out by professionals, and have the risks associated with the trial minimised. On the other hand, lives must be saved even though children may not be able to consent, and poor countries may not have trained professionals to carry out the trials. It’s all about balance.

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