This report will look at the history of cholera and the similarities between the first outbreaks and now, and will also look at why there are still cholera outbreaks today. Other topics looked at include how climate change can make a difference and what the implications are of having so much more traffic of people coming and going by air travel now.
The Blue Death, also known as Cholera, is a contagious bacterial intestinal infection which is caused by drinking contaminated water. The bacterium which causes this is called vibrio cholerae and affects the small intestine with symptoms of severe diarrhoea, vomiting and dehydration. Most affected are small children and the elderly, with most cases resulting in death due to the amount of body water lost. Up until a hundred years ago, cholera was a public health issue in Europe but with improved sanitation and treatments of drinking water, the disease has pretty much been eliminated in developed countries. Cholera pandemics have usually occurred in developing countries where there is poor sanitation and water treatment; however there have been outbreaks in Europe and the US, the most recent one being in Haiti.
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Image of vibrio cholerae bacterium
Let's take a brief look at the history of cholera. John Snow (1813-1856) was a British physician and surgeon-apothecary and is considered one the founders of epidemiology for his research into finding the source of the cholera outbreak in the 19th century.. Scientists at that time had identified the humoral model of disease and later the miasma model as the cause for outbreaks of cholera. However, John Snow had different opinions and started his own research to find what he thought was the cause of cholera. It was through his research that he was able to determine the cause, and he used models to help him in his findings. Models are analogies that help clarify hypotheses - proposed explanations of relationships between causes and effects, and play a very important and significant role in testing hypotheses. They allow scientists to investigate their findings and often in a variety of different ways. As well as putting practise into action, it allows scientists to observe their hypotheses at work. However, using animal models does not accurately relate to humans but still gives an insight into what the expected results may be. Only after successfully testing on animals would scientists then look for human volunteers, and this is due to ethics. In this instance, Snow's use of animal models led him to question findings that he had learned about toxic gas and as such gave way to a new hypothesis.
The humoral model of disease proposed that cholera was caused by an imbalance in one of more of the following fluids; blood, phlegm and black and yellow bile. These four were termed the 'humors' and treatment was applied by the physicians own interpretation of the humoral imbalance so was very varied. Often purgatives and emetics were prescribed to balance the system. Some treatments even included the use of leeches to get rid of the bad blood in the body. However, scientists later developed the miasma model of disease which proposed that cholera was an epidemic disease which could be the cause of exposure to some sort of toxic gas or miasma and the medical orthodoxy at that time believed that the toxic gas was a result of the fermentation of organic material such as human waste. This resulted in early promoters of public health focusing on the removal of cesspools and piles of composting faeces, with the main aim being to build a network of sewer pipes that would carry waste material into the River Thames.
After the first cholera outbreak in 1831, John Snow went on to do further medical studies and then practised surgery in a hospital in London. Anaesthesia was not used in surgery at that time and Snow had read about it being used and actually got to see one of the first demonstrations of it being employed. This led to Snow recognising that there was a lack of control over the precise dosage of anaesthesia required so he started to experiment and develop devices that would accurately measure precise doses, eventually designing gauges and masks as well as using a variety of animal models to test on. It was a result of this experimentation that led him to question the miasma model of disease for the cause of cholera, as what he had learned about toxic gas did not seem consistent with epidemics.
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Snow's research on anaesthesia was experimental, unlike his work on cholera, so firstly the basic skills of experimenting were necessary coupled with deep curiosity to find out the way things work and how they have certain effects on certain things, in other words; careful, systematic observations. A scientific background would be highly advantageous and you have to be prepared to accept the fact that things may not turn out properly. For planning effective experiments to test dosage measurements a scientist had to have the necessary equipment or improvise if necessary, and be able to do so with some degree of accuracy and also be able to record the results in an accurate way so that they could easily be interpreted. The ability to record results in a variety of different ways, like graphs, charts and tables, was also essential. The scientist had to have a general knowledge and interest in what they wished to experiment and all results had to be carefully and meticulously recorded so a great deal of patience was also required. Designing contrasting observations could also be a good way to test hypotheses as well as using different types of models to record the effects and properties of certain drugs. The use of models would also be beneficial in monitoring accurate delivery systems for anaesthesia.
Therefore, experiments are considered strong tests of hypotheses because they ultimately test them and can either support them or come up with alternative ones. Sometimes several experiments could be conducted and that could exclude one or more of the hypotheses. They also allow results to be analysed and conclusions to be reached and often scientists could form some sort of theory based on the results of an experiment which can then be put into research papers to be discussed thus publicising the findings of experiments. It is imperative that experiment results are recorded accurately. An important fact to remember is that experiments only support hypotheses; they can never prove it right or wrong. A control experiment would be set up so that any change could be monitored and this control would be neutral.
As mentioned before, it was Snow's experiments with anaesthesiology and working with gases that led him to recognise that the patterns of cholera outbreaks were inconsistent with the patterns that would be expected from poising by toxic gas, and because he couldn't induce cholera in animal models, he realised he would have to try a different approach. He also found the symptoms of cholera to be inconsistent with symptoms that would be shown if exposed to toxic gas. Cholera was often called the 'blue death' as it would cause a person's skin to turn blue due to respiratory failure resulting in death and is caused by the bacterium vibro cholerae, causing severe diarrhoea and dehydration with death occurring due to such a extreme loss of body fluid. It is mainly transmitted through contaminated water, but can also be spread through food such as fish and shellfish from contaminated water, and produces toxins which cause the symptoms.
John Snow believed that cholera was caused by either eating or drinking something that was contaminated because the gastrointestinal symptoms seemed to be more consistent with this rather than toxic gas poisoning. He tried to convince his fellow scientists that cholera was transmitted through contaminated water but his ideas were not accepted at this early date due to the fact that scientists rarely agree on things. They all had different explanations and formulated their own experiments and collected data and did not want to know that their theory could be flawed or there could be another explanation. Due to the fact that there was lack of evidence to support Snow's ideas, they were dismissed and generally ignored as people accepted the miasma model of disease as the cause of cholera.
Symptoms of cholera
Cholera outbreaks are more consistent with contamination of water than air due to the fact that in 1854 London there was no running water in homes so people had to use a communal water pump that served particular neighbourhoods. This meant everyone was sharing the same water supply. John Snow had mapped locations of the pumps where cholera outbreaks occurred and collected evidence that everyone who got sick all took water from the same pump. It was his belief that cholera was spread by contaminated water and therefore was confined to a particular area, whereas if it were due to contaminated air, then there would be more widespread cases in London at the time and the outbreak would have spread quicker. Also, none of the doctor's treating patients had contracted cholera themselves so this suggests that it could not have been air contamination. However, the miasma model persisted because medical theory at the time believed the disease was cause by contaminated air, usually derived from decaying organic matter. This meant that people were more worried about atmosphere pollution rather than water, and the fact that there was little evidence to support Snow's theories at the time. The general medical opinion was that because the air can be corrupted by perspiration, dirt and faeces, the squalid living conditions were blamed for cholera outbreaks. As a result of this, John Snow realised that he would have to find a different way to test his hypothesis.
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While Snow did not have a background in epidemiology, his past research on anaesthesia helped him design a new model for the cause of cholera because he already had experience of using experimental techniques. His approach to the research on cholera was similar to the research he did on anaesthesia, and started with clinical observations, followed by forming a hypothesis which then resulted in a theory being formed. His observations were not only based on his experiences in dealing with patients of the firs cholera outbreak, but also on the experiences of others plus extensive examination of medical literature available at the time. He realised that there was no possible way to do an experimental test of his hypothesis so he had to look for other ways to do these tests. So he did extensive research of all available records and tried to find some sort of pattern. He also noticed that there was severe lack of personal hygiene and overcrowding at the time which he associated with cholera and concluded that it was spread by contaminated water.
After Snow published a research paper in 1849 regarding cholera, it was suggested by a journalist that an experiment should be conducted of people living side by side with similar lifestyles but only the water source should be varied. This would provide critical evidence as it would basically be testing Snow's hypothesis about cholera being transmitted through contaminated water. If one side was given water from a contaminated source and the other side given sterile, boiled water, then the outcome would result in only one side displaying cholera symptoms. It would show that cholera was spread by drinking contaminated water.
Between 1860 and 1865, Louis Pasteur (1822-1895) proposed the germ theory of disease which proved that most infectious diseases were caused by micro-organisms. He worked with French wine growers and helped with the fermentation process to develop pasteurisation, which is a method that killed germs. Initially he did his research with wine and beers, and demonstrated that bacteria were responsible for beer and wine going sour, later on applying the same principle to milk. He found that harmful bacteria could be removed by boiling a liquid and then letting it cool down, and this is known as pasteurisation. It was this discovery that supported Snow's hypothesis about cholera being transmitted through contaminated drinking water.
This led to Snow questioning public health and did more research into the topic, doing door to door interviews of families affected by cholera and interviewing doctors that had treated cholera patients. Working alongside Snow was William Farr (1807-1883), who was keeping records of births and deaths on London and they were looking for some sort of pattern. Snow started looking at the geographic distribution of cholera outbreaks compared to the sources of drinking water available and mapped where the cholera deaths occurred. He was trying to verify the source of the water as it would help him trace where the outbreak may be stemming from. Snow found that by comparing a neighbourhood by their source of water supplier would give him a better idea of where the contamination may be and he could basically use it as an experiment using one side as a control and then recording the results. If he looked at two neighbourhoods with their own water source then it would be more difficult to pinpoint where the contamination could be since there were two separate sources, whereas with just the one neighbourhood, it would be easier to see and record the results. The variables that were included in a casual web for cholera are living conditions, public health, water sources and illness at the time. Snow saw his conclusions about cholera to be inferences based on his observations whereas the medical journal reviewer considered these to be conjectures. An inference is a conclusion drawn from background knowledge and facts, whereas a conjecture is based on speculation which has not been proved.
In 1854, there was another cholera outbreak near the Broad Street pump. Snow believed that the outbreak was caused there by the lack of proper sanitation and the general squalor of living conditions. His hypothesis was that contaminated water from nearby cesspools was somehow leaking into the water supply, causing this outbreak of cholera. He had to do some non-experimental tests so resorted to going door to door asking specific questions and trying to identify a pattern again. He took his findings to the Parish Board and presented his findings, asking them to remove the handle on the Broad Street pump. This was regarded with scepticism at first but the handle was removed and eventually the number of cholera cases dropped.
Cholera outbreaks in Broad Street, London 1854
Snow focused on households that were affected by the cholera outbreak and conducted his interviews in those neighbourhoods to gather his evidence. However, a minister of St James Church, Reverend Henry Whitehead, who was sceptical of Snow's explanations, started conducting his own interviews but he focused on households which were not affected by cholera and found that households using the pump at Broad Street were nine times more likely to contract cholera than those who didn't use it. In this way, he improved on Snow's test of his hypothesis and actually identified where the first incident of cholera started - it was an infant living just a few feet from the pump that had died from diarrhoea a couple of days before the outbreak. The two ended up working together, eventually asking the Board of Public Health to dig up the area around the pump to try and identify the cause. When the area had been excavated, they found that water had been leaking from a cesspool under the building where the infant had died and this was seeping into the water supply at the pump. After making further inquiries, they found out that the infant's mother had actually washed the soiled diapers of the sick child in the basement of her building and then dumped the water into the cesspool near the pump. The main difference between correlation and causation is that correlation describes the relationship between two things or variables whereas causation is causing something to happen. In this case, Snow and Whitehead looked at the correlation aspect of why there were still cholera outbreaks. After the excavation of the area around the pump revealed the contaminated water of cesspools leaking into the drinking water supply and after a drought the following summer, Members of Parliament voted to start a project that would improve the sewer system and move the sewer pipes further downstream of the Thames in order to prevent further outbreaks of cholera.
After the construction of new sewer systems in England, there were no further outbreaks but some have still occurred mostly in developing countries around the world, for example the outbreak in Peru in 1991, which caused a lot of deaths. The most recent outbreak has been in Haiti.
The main difference between public health in the 19th century and now is that there is a lot more awareness now and things have been greatly improved, especially with the invention of the water closet and the sewer systems being improved. However, as mentioned, there has been a recent cholera outbreak in Haiti, which was confirmed on October 21st 2010. This is thought to have been caused by breaches in the water supply, sanitation and hygiene infrastructure used by large groups of people causing exposure to contaminated water or food and in order for it to occur in the first place, it's thought that it had to be present among the population but how this could happen is still unknown.
Climate change could play a big part in the spread of cholera, as the bacteria can lie dormant for long periods of time, and due to global warming and rising water temperatures the bacteria is given the opportunity to come active and start multiplying. In extreme heat conditions, the bacterium would multiply quickly in stagnant pools of water and in extreme wet conditions the bacterium can spread by overflowing rivers. Also, animals in the water can end up eating the bacterium and these animals are then eaten by humans, causing the spread of cholera.
These days, travel has become a lot more commonplace and this greatly increases the chances of cholera spreading from one country to another, especially overseas. To combat this, awareness has been raised about these concerns and if travelling to a different country, the general advice is to boil any water before drinking to make sure that any harmful bacteria are killed, thus reducing the chances of becoming ill or contracting something. However, this is not guaranteed to stop the spread of cholera as the bacterium can lay dormant and could basically be in most creatures in the sea that are consumed as delicacies, especially the ones that are eaten raw.
In conclusion, due to the improved public health and sanitation in developed countries, cholera is no longer a problem. However, it is still a problem in developing countries, where the public health and living conditions are not as good as the developed countries and there seems to be a general lack of education when it comes to personal hygiene and cleanliness. The outbreaks of cholera generally tend to be focused around areas that have no running water and have to chare a communal water supply. This greatly increases the risk of the bacterium spreading.
One can only hope that with continued dedication and education, awareness can be raised with regards to sanitation and public health, but sadly the conditions in some countries lead to outbreaks, as often there is not enough money for proper sewer systems or education for the people. Crowded living conditions coupled with natural disasters also increase the risk of cholera outbreaks. To sum it all up, hopefully one day cholera will be wiped out, but as it stands just now, this is something that will most likely keep occurring due to the fact that some countries are better off than others. After all, everyone prays for the day where disease and death will no longer be the main issue of day to day life.