How cholera evolved to be one of the deadliest diseases in historyS

Cholera has long been a known disease, but it wasn't until the 1700s that it was recognized as a worldwide plague. It became one of the most feared diseases in the world because it adapted to humans enough to take control of our basic bodily functions.

Love in the Time of Cholera is a beautiful novel that illustrates two things - that cholera was once so pervasive and sweeping that it marked out a whole time period, and that cholera has been so successfully repressed in the developed world that we invoke it in romantic novels despite the fact that it kills people by making them shoot all the liquid in their body out of their anus. Yeah, that title looks different now, doesn't it? It's not as romantic to think of Florentino and Fermina wading through - and narrowly avoiding eating - other people's crap. But that is how cholera spreads, and that is why there was a "time" of it.

How cholera evolved to be one of the deadliest diseases in historyS

Cholera Multiplies in the Body

Cholera is the name of the disease caused by ingestion of the bacterium Vibrio cholerae. Once in a human body, the bacterium perpetuates itself via an incredibly efficient process. It shoots vigorously through the digestive system until it comes to the small intestine. The small intestine is responsible, among other things, for keeping the right balance of water in the body. It does this by passing water back and forth through a layer of epithelial cells. Often these cells grab the extra water molecules out of whatever is making its way through the intestine and retaining the water for the body. When a person eats something that disagrees with them, either because it has parasites or because it is poisonous, the body pumps water from the body through the layer of cells and into the small intestine, which lets the misbehaving food flow through quickly out of the body and do as little damage as possible. The process involves stealing a lot of water from the rest of the body, which is why it's so important for people who have diarrhea to drink liquids. They need to replace the water they lost.

When Vibrio cholerae enters the body it puts out a certain toxin that attacks the junctions between the epithelial cells, ripping them apart. Water pours through the breaks between the cells and goes out the only available exit. So many epithelial cells come off during this process that they resemble small confetti-like flakes and have given the excretions of cholera patients the name "rice water." "Rice water" is also filled with more bacteria, which go out into the world ready to spread the disease. These bacteria were once quite mild-mannered, and even today can be managed with clean drinking water and, if necessary, a couple of IV bags of fluid.

How cholera evolved to be one of the deadliest diseases in historyS

Cholera Multiplies In the World

That's where humans come in. For most of human history, clean drinking water wasn't too far away. When people wandered in small groups, they could excrete gallons of bacteria-filled fluid and the people caring for them could move upriver for clean water. Even small settlements had no difficult time setting aside areas for clean drinking water. If a strain of Vibrio cholerae was to be successful, it couldn't wring a person out like a dishrag and kill them quickly. It was the strain that lingered, keeping its host sick but alive, that had the best chance of spreading - through a moment of carelessness - to the people nearby.

It was when people began crowding together in larger groups, when drinking water and waste water started mixing, that the balance between the more benign cholera and the more virulent cholera shifted. Suddenly there was no percentage in sticking around and hoping that the people around the human host got careless as to where they put their hands (and how soon afterwards they put their hands in their mouths). The advantage went to the bacteria that reproduced like crazy and spread themselves through the dense population. This is when cholera turned into a fast, terrifying killer. By the 1800s, cholera could kill people twelve hours after their first symptoms appeared. They were drained of up to fifteen percent of their body weight within a few hours. For the most part they died of dehydration and electrolyte imbalance, but not before spewing out more bacteria into the general water supply.

And this is why the developed world is no longer in the time of cholera. Certainly, knowledge of how it spreads, and how it can be combated, helps. What helps more is the fact that sewage systems and drinking water systems exist, and are kept separate. It's also why any large human settlements that by disaster or bad design accidentally mix the two systems suddenly dip back into the bygone era again. This is a time we carry with us.

[Via UCSD News, The Ghost Map]

Virus Images: Dartmouth College