Cholera

What is Cholera?

The Vibrio Cholerae bacterium causes cholera, which is an infectious disease with effects similar to that of gastroenteritis, which affects the way in which the small intestine works, causing diarrhoea, dehydration and potentially, death.

A Vibrio Cholerae bacterium

Transmission

The most common method for cholera to be transmitted to a patient is through waterborne sources. Cholera infected waste from cholera sufferers can easily contaminate water sources and food. It is from this contamination that cholera can infect further patients. The bacterium is consumed with the contaminated source, for example fish or drinking water. The cholera then makes its way through the human digestive system.

This is more common in countries where sanitation is poor and water sources are easily contaminated. In Haiti in 2010 after a large earthquake main water sources became contaminated and an outbreak of cholera occurred. This epidemic claimed the lives of 5,506 Haitians by June 2011 and still infects more every day. Any natural disaster or war increases the chances of an outbreak of cholera and it is thus more prominent in areas of Africa where civil war is a common occurrence.

The Vibrio Cholerae bacterium survives the hostile conditions of the stomach by shutting down the production of nearly all nutrients and conserving energy until it is passed into the small intestine. In the small intestine the bacterium maintains flagella proteins and uses these to propel itself to the where it shall release its toxins. When the bacterium has completed its journey into the correct area of the small intestine it shuts down production of flagella proteins to further conserve energy.

Causes

In an uninfected human the water in food and drink osmoses from the lumen through the epithelial cells in the walls of the small intestine, this allows it to enter the bloodstream and be taken the areas of the body where it is needed. For successful osmosis, chloride channels between certain epithelial cells allow chloride ions to create an unbalanced concentration gradient between the lumen and the exterior of the intestine, to achieve a state of molecular equilibrium the water osmoses out of the lumen.

A diagram demonstrating the effects
of the cholera toxin on the epithelial cells
in the small intestine.
When the cholera bacterium reaches this area of the intestine it releases toxins, which bind to specific receptors on the epithelial cells, entering the cell through cell-mediated endocytosis, and opens the chloride channels, causing the concentration gradient to reverse. Chloride ions flow into the lumen and water now osmoses from the high water potential in the blood to the low water potential in the lumen down the concentration gradient. The body is now dehydrating itself through the osmosis and the body is not absorbing water. This is the cause of the majority of symptoms of diarrhoea and dehydration, as it is simply flushed through the body.

Symptoms

The most prominent symptom experienced by sufferers of cholera (as with most forms of gastroenteritis) is intense watery diarrhoea with a distinctive ‘fishy’ odour; this expulsion is classifiable as type 7 on 'Meyer's Scale' and causes severe dehydration in those infected. In an untreated case of cholera, a sufferer may excrete 10-20 litres of faecal matter every day. Sufferers may also experience vomiting.

Sufferers will experience low blood pressure and maintain a rapid pulse. As the bacterium affects their body, their appearance will change through sunken eyes and low skin tugor. Some sufferers will experience varying levels of acidosis.

Symptoms of cholera can include sunken eyes
and decreased skin turgor.

Treatments

Oral re-hydration solutions in poor countries are available from the WHO to help keep the patient alive throughout the duration of their infection and maintain their level of hydration. If a sufferer is severely dehydrated, then rehydration should be done as an intra-venous drip directly into the bloodstream.

Potassium replacement medicines are administered if the sufferer is experiencing acidosis so as to build the levels of potassium back to norms; these can also be administered orally or using an IV drip. Antibiotics can be administered as to fight the bacterium and greatly shorten the length of time that the sufferer is infected.

Cholera wards use specialised beds to allow the patients to expel the diarrhoea whilst remaining in their beds, a collector (usually a bucket) is placed underneath a hole in the bed allowing for the waste to be disposed of safely and decrease risk of others becoming infected. 

The mortality rate for an untreated sufferer of cholera is 50-60%.

References

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