Monday, 20 February 2012

Dirty water in the time of cholera

I have a slight obsession with the sewers, which I don’t think is entirely normal or healthy. It’s the architecture more than the sewage itself but, as it happens, this post concerns the latter. Our tour of interesting things poo-related starts in London of 1858 and a period of history known as the Great Stink.

The first half of the 19th century saw the population of London soar to 2.5 million and that is a whole lot of sewage—something like 50 tonnes a day. It is estimated that before the Great Stink, there were around 200,000 cesspools distributed across London. Because it cost money to empty a cesspit, they would often overflow—cellars were flooded with sewage and, on more than one occasion, people are reported to have fallen through rotten floorboards and to have drowned in the cesspits beneath.

Sewage from the overflowing cesspits merged with factory and slaughterhouse waste, before ending up in the River Thames. By 1958, the Thames was overflowing with sewage and a particularly warm summer didn't help matters by encouraging the growth of bacteria. The resulting smell is hard to imagine, but it would have been particularly rich in rotten egg flavoured hydrogen sulphide and apparently got so bad that the House of Commons resorted to draping curtains soaked in chloride of lime in an attempt to block out the stench and even considered evacuating to a location outside the city.

At the same time, London was suffering from widespread outbreaks of cholera; a disease characterised by watery diarrhea, vomiting and, back in the 19th century, rapid death. But no one really knew where cholera came from. The most widely accepted theory was that it was spread by air-borne ‘miasma’, or ‘bad air’. Florence Nightingale was a proponent of this theory and worked hard to endure hospitals were kept fresh-smelling and that nurses would ‘keep the air [the patient] breathes as pure as the external air’. However, when it came to cholera, this theory was completely wrong.

A doctor called John Snow was one of the first people to suggest that the disease was transmitted by sewage-contaminated water—something of which there was a lot in 19th century London. Supporting his hypothesis was the 1854 cholera outbreak in Soho. During the first few days, 127 people on or near Broad Street died and, by the time the outbreak came to an end, the death toll was at 616 people. Dr Snow managed to identify the source as the public water pump on Broad Street and he convinced the council to remove the pump handle to stop any further infections (although it is thought the outbreak was already diminishing all by itself by this point).

From a 19th Century journalist on the problem of cholera in London:
A fatal case of cholera occurred at the end of 1852 in Ashby-street, close to the "Paradise" of King's-cross - a street without any drainage, and full of cesspools. This death took place in the back parlour on the ground floor abutting on the yard containing a foul cesspool and untrapped drain, and where the broken pavement, when pressed with the foot, yielded a black, pitchy, half liquid matter in all directions. The inhabitants, although Irish, agreed to attend to all advice given to them as far as they were able, and a coffin was offered to them by the parish. They said that they would like to wait until the next morning (it was on Thursday evening that the woman died), as the son was anxious, if he could raise the money, to bury his mother himself; but they agreed, contrary to their custom on such [-55-] occasions, to lock up the corpse at twelve o'clock at night, and allow no one to be in the room. On Friday, the day after death, the woman was buried, and so far it was creditable to these poor people, since they gave up their own desires and customs, which bade them retain the body.

George Godwin, 1854 - Chapter 9, via

The London sewage problem was finally addressed by the introduction of an extensive sewage system overseen by the engineer Joseph Bazalgette. In total, his team built 82 miles of underground sewers and 1,100 miles of street sewers at a cost of £4.2 million and taking nearly 10 years to complete.

London sewer system opening - via bbc

We now know that cholera is caused by a bacterium called Vibrio cholerae. In order to become pathogenic to humans, the originally environmental bacterium needs to acquire two bacteriophages (viruses that integrate into the bacterium’s genome)—one that provides the bacterium with the ability to attach to the host’s intestinal cells and one that leads to secretion of a toxin that results in the severe diarrhea associated with this disease.

Now I don’t often get teary-eyed at scientific meetings but, several years ago, a lecture by a guy called Richard Cash made me remember why I’d got into science in the first place. See, cholera is a disease which kills around 50-60% of those infected (sometimes within hours of the first symptoms) but with treatment, the mortality rate drops to less than 1%. And the reason that this disease is now almost completely curable is down to Professor Cash. The problem with cholera is that a patient can lose something like 20-30 litres of fluid a day and death occurs due to dehydration. So Cash and his team came up with an unbelievably simple solution—replace the patient’s fluid and electrolytes as quickly as they are lost. Oral rehydration therapy is a solution of salts and sugars, and is thought to have saved something like 60 million lives since its introduction. Patients who would have died within hours can now make a recovery within a day or two. Awesome, right?

Today, we tend to hear of cholera mainly when it is associated with natural disasters where contaminated water can spread disease throughout a region where the infrastructure has been severely compromised. One of the most recent outbreaks occurred nearly a year after the Haiti earthquake—cholera left over 6,00 dead and caused nearly 350,000 cases. But, prior to the outbreak, Haiti had been cholera-free for half a century. So where did it come from?

Image available from Wikipedia commons

I mentioned earlier that cholera can result from an environmental strain of bacteria acquiring the phages encoding virulence factors. But, unfortunately, the Haiti outbreak was actually brought into the country by the people trying to help rebuild following the earthquake. By comparing the DNA sequence of the outbreak strain with strains known to infect other parts of the world, it was possible to narrow down the source of the outbreak to Nepal. And UN peacekeepers from Nepal were known to be based near the river responsible for the first cases. It is highly likely that it was one of these soldiers who brought the disease to Haiti and this case demonstrates how quickly cholera can spread if gets into the water system. Lessons learnt from this outbreak will hopefully lead to visitors from cholera-endemic countries being vaccinated before travelling to post-disaster areas, even if they are showing no sign of the disease. After all, something close to 3 in 100 patients remain asymptomatic after infection.

The biggest obstacle in the way of eradicating cholera today is poor sanitation leading to contamination of drinking water. In some parts of the world, the link between hygiene and disease prevention is not as obvious as it is to us in the Western world. Cholera isn’t a disease which requires complicated drugs or vaccines to prevent—washing hands with soap, avoiding contact with human waste, and clean drinking water would make all the difference. 


Bronx NY Sewer & Drain Cleaning said...

Don’t waste your time cleaning sewers. Let Bronx Sewer Cleaning handle it!

Manar Koutb said...

في شركة شركة تسليك مجارى نعمل قدر الامكان علي حل المشكلة واعطاء العميل فكرة كاملة عن الوضع وكذلك التكاليف المفترض دفعها مع العمل علي اصلاح وصيانة مكان التسرب فقط وليس البدء من الصفر داخل الحمامات او المطابخ كما نقدم في شركة شركة تسليك بالوعة المطبخ كافة خدمات الصيانة بعد الكشف ويشمل ذلك ( تكسير – اصلاح – ترميم ) كل ذلك بخدمات مميزة وفنيين علي كفائة عالية جدا ومعدات حديثة تضمن صحة النتائج لذلك تعد ركن نجد افضل شركة تسليك مجارى بالرياض
للمزيد يمكن زيارة
شركات تسليك المجارى بغرفة التفتيش والتي غالبا ما تحدث فيها الكتمة عن طريق سقوط مخلفات صلبة فيها او بقايا اعمال التشطيبات المترسبة فيها وهو ما يتم عن طريق سوستة الضغط او عن طريق غطاس ضغط المياه.

تسليك بالوعة الحمام
شركة تسليك مجارى بالرياض
شركة تسليك المجاري بالرياض
شركة تسليك مجاري

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