I got bored with vaccination. Here’s something about cholera!
Recently there has been an outbreak of cholera in Haiti, with a death toll of over 300 so far. Although newsworthy because of the location, this is a small drop in the 100 000 – 200 000 cholera deaths that occur every year. In addition to being one of the top killers of infants worldwide through diarrhoea and dehydration, cholera also was responsible for the conception of modern epidemiology.
Cholera! What a fantastic word. The origin of the word is not exactly known, but there are a couple of popular theories: 1) coming from a combination of the Greek words chole meaning “bile” and rein meaning “to flow”, cholera may have been first described as a flowing of bile out of the intestines into the rest of the world or; 2) the Greek word cholera meaning a roofing gutter, a possible metaphor for the torrents of stool that come streaming out of the patient when struck down with the disease. In either case, the term refers to the most significant symptom of cholera – diarrhoea.
About 4 million people are infected with cholera each year, though this figure has jumped up in past during global pandemics. 75% of cholera cases do not result in any disease at all, but for the rest, cholera can kill within hours. 20% of symptomatic patients experience severe diarrhoea; they lose so much water that it washes away everything in the gut, resulting in “rice-water stool”. Patients can lose up to 20L of fluid through diarrhoea DAILY for weeks on end. In cholera wards, they don’t bother with toilets or bedpans, they just drill a hole in a bed and put a bucket underneath. Treatment for patients is simply continuous rehydration until they clear the disease.
Though it has been acknowledged since ancient times, the cause and even how it was transmitted was only recently discovered. For this, we have John Snow to thank. The famous story of John Snow and the Broad Street pump is a tale of one man’s victorious scientific struggle to disprove the theory that cholera was spread through the air by vandalising a water pump to stem the source of cholera to hundreds of Londoners.
In the summer of 1854, London was struck down with an epidemic of cholera. Fear was rampant throughout the streets. Some people believed that cholera was spread by a miasma, caused by the stinking wafts of garbage and open sewers. Rumour had it that cats were causing the epidemic, and tens of thousands were rounded up and killed. Amidst people literally shitting themselves to death from cholera, John Snow hypothesised that it was actually being spread by contaminated water. Being a scientist, he needed proof. So he (and any medical professionals he could convince) did a survey of the neighbourhood which they thought was most afflicted by the disease. Snow himself canvassed more than 600 households, asking if anyone in their household had died from cholera recently. Painstakingly, he mapped the deaths out and found them distributed around a common point: the Broad Street water pump, where families sourced their drinking water. With defiance and in the face of criticism from the municipal government, Snow marched to the water pump and tore loose the handle, saving hundreds of Londoners and ending the epidemic.
This is one of the long-standing great stories of science. Too bad the achievements attributed to Snow are somewhat embellished. The epidemic was already waning by the time of Snow’s intervention, mostly because people were (understandably) moving away from Broad St. Also, Snow himself didn’t actually remove the handle, but ended up convincing the doubtful authorities with the strong data he produced. But this does not take away one bit of Snow’s contributions to transmission of cholera and the importance to discover and interdict the route of transmission of an infectious disease during an outbreak.
We now know that the bacterium Vibrio cholerae (a cousin of the species responsible for puffer-fish poison) is the causative agent for cholera. After gaining access to patients through the drinking of contaminated water, V. cholerae sets up shop in the gut and reproduces to very high concentrations by using the delicious nutrients in your intestines. To disperse itself as widely as possible, the bacteria secrete a toxin that reverses the flow of water in your intestines. So now instead of absorbing water, your intestine excretes water, leading to the diarrhoea. In areas where water and waste infrastructure is poor (or becomes poor due to, say, earthquakes), the bacteria-laden diarrhoea can find its way to a source of drinking water and start the cycle all over again.
So the happenings in Haiti are indeed a big deal and could get bigger as health workers defend the capital against infiltration by cholera. Only time will tell whether they are successful or not.
Paneth, N. (2004). Assessing the Contributions of John Snow to Epidemiology Epidemiology, 15 (5), 514-516 DOI: 10.1097/01.ede.0000135915.94799.00