Cholera (Cambridge O Level Biology)

Cholera causes diarrhoea

• Diarrhoea is the loss of large volumes of watery faeces from the anus
• If it is severe and continues for a long time, it can lead to death by dehydration
• Severe diarrhoea can cause the loss of significant amounts of water and ions from the body, causing the tissues and organs to stop working properly
• It can be effectively treated by oral rehydration therapy
• This is a drink with a small amount of salt and sugar dissolved in it
• There are many causes of diarrhoea, one of which is infection with the bacterium Vibrio cholerae, which causes the disease cholera

CDC, Public domain, via Wikimedia Commons

The pathogen Vibrio cholerae can cause cholera

How does Vibrio cholerae cause diarrhoea?

When V. cholerae is ingested via infected water or food and enters the small intestine, it can cause illness as follows:

1. Bacteria attach to the wall of the small intestine
2. They produce a toxin
3. The toxin stimulates the cells lining the intestine to release chloride ions from inside the cells into the lumen of the intestine
4. The chloride ions accumulate in the lumen of the small intestine and lower the water concentration there
5. Once the water concentration is lower than that of the cells lining the intestine, water starts to move out of the cells into the intestine (by osmosis)
6. Large quantities of water are lost from the body in watery faeces
7. The blood contains too few chloride ions and water

Diarrhoea is a symptom of cholera; it can lead to severe dehydration and death