How does a river fight disease? By making your illness catch a cold.

The river Ganga has always been known for its healing powers and the purity of its water. Even when stored for a long time, Ganga water doesn’t become bad and putrid. And it doesn’t stop there: a 2009 study showed that the E. coli virus, which causes food poisoning and spreads through water, doesn’t last as long in Ganga jal. When bred in the river’s water, the bacteria died out within five days.

It’s not just E. coli. As far back as 1896, European scientist Ernest Hankin found the Ganga’s water to be an effective cure against cholera-causing Vibrio cholerae. In India, of course, its healing powers had been common knowledge for centuries before.

Clearly, there’s something in the water that’s killing these bacteria. But what?

There are two kinds of infections: viral and bacterial. Bacteria are small creatures that get into your body. Many do things that you’d want them to do, like helping you digest food. But there are bacteria that do things you don’t want them to do: those are the ones you would call “infections”.

Viruses, on the other hand, are not creatures at all. That is to say, they’re not alive: viruses are small strands of DNA or RNA, which are manuals that contain instructions on how a cell should build itself in order to grow into a light-detecting cell or a wing-muscle cell or whatever else it’s supposed to become.

But when the virus gets into the cell, the instructions it gives are quite different. They simply say: “Make more copies of me.” Viruses are DNA too, so the cell complies.

If this happens too intensively, the cells don’t have time or energy to do anything else. And when that happens too extensively, you fall ill.

Over time, people can develop a resistance to certain kinds of bacteria and viruses. That could mean their bodies destroy the infection completely, or it could simply mean they don’t get as badly affected anymore. This is useful because it makes viruses less deadly — but it also means people have to worry about invasions by other people.

When European humans first came to America, they took many European viruses along with them. The Americans had never met the viruses before, and didn’t have any resistance to them at all. What gave Europeans smallpox would kill the Americans in a matter of days.

The Europeans took advantage of this. Once, they even “gifted” blankets to the Americans, but the blankets turned out to be infested with smallpox virus. Mostly, however, they didn’t have to do a thing. The viruses travelled forth on their own, and by the time the European invaders reached, the Americans were already too sick and weak to fight back.

Nowadays, countries can even develop bacteria and viruses as weapons. But because there are laws that say that it’s an unfair way to fight a war, they can only do it illegally.

That doesn’t mean armies aren’t interested in bacteria. They’re just interested in them slightly differently: how to prevent bacteria from eating their food.

If you leave a samosa on the Moon, it wouldn’t get spoilt. Food doesn’t “go bad” or rot on its own: it does it because of the small bacteria inside that eats and digests it. If it wasn’t for those bacteria, the food would last, if not forever, then at least for a very long time (unless it’s ice-cream).

It doesn’t have to be out of this planet, either. Millions of years ago, ancient trees fell and were buried in swamps, where bacteria couldn’t reach them. Those trees didn’t decompose into soil. Instead, they stayed on, getting more and more compressed until they finally turned into coal and rock.

Some of them are now visible as fossilised forests. The others provide fuel for the car you’ll use to get there.

Armies want to achieve the same effect as the swamp and the moon: they want bacteria to stop eating their food, so that they can eat it instead.

Other people may want this too, but the problem is especially big for armies. Soldiers may be posted in remote, out-of-the-way areas, with no contact with the rest of the world. They’ll have to carry food supplies with them. And, those food supplies will have to last.

Food and battle have always been connected — including one food competition held to help feed Napoleon’s army. But things really came to a head during the Second World War, when armies everywhere were running out of rations.

After the war, the U.S. military decided never to be caught unprepared again. So they began researching different processes and preservatives to stop food from getting spoilt. The aim was to stop bacteria from coming into the food —both by more efficient packing, and by putting special additives that bacteria find poisonous.

All this worked well, but there was one problem: it was expensive. Making food this way took a lot of effort. What’s more, there weren’t enough factories to provide it in the necessary amounts if war did break out.

So the U.S. military began sharing its technology with commercial food-companies. Those companies could sell the food to ordinary people on a large scale, making it cheaper to produce. And when a war came, all those companies’ food-factories would be up and running, ready to pitch in.

Of course, there’s another result: everyone who buys processed food from supermarkets is, without realising it, surviving on military rations.

It’s not just processed food that people protect from bacteria. They do it to food that’s alive, too.

Chicken-farm owners, for example, like to stop bacteria from coming in and giving their chickens disease. That’s actually a problem in some places. Chicken-farms in India use a lot of antibiotics, including ones they shouldn’t.

Antibiotics are chemical substances that kill bacteria. For bacteria, they’re poison (they don’t do anything to viruses, though). People with bacteria-caused diseases often take antibiotics to make them go away. There’s only one problem: bacteria develop resistance.

Just as humans become resistant to certain bacteria, so bacteria become can resistant to certain antibiotics. Bacteria evolve much faster than humans, and can quickly adapt into new “strains” that are resistant to certain antibiotics. What’s more, they can share that resistance. The more an antibiotic is used, the more resistant the bacteria grow.

To avoid resistance, antibiotics need to be used sparingly. They should be avoided for diseases that peoples’ bodies can handle themselves, and, when they’re used, they should be used thoroughly to make sure there are no survivors. After all, it’s the surviving bacteria that develop the resistance and pass it down the generations.

But all that careful usage by humans doesn’t help if the same antibiotics are being used indiscriminately for chickens.

At the chicken-farms bacteria are constantly coming in touch with antibiotics — and learning how to deal with them.

It’s not just chickens, though. Humans have been careless with antibiotics too, especially when patients want “something more” to help in the cure, and unscrupulous doctors want to make extra money by selling them.

Like a magic spell that wears off over time, antibiotics are slowly losing their power.

Many bacteria can now ignore common antibiotics, and doctors have to fall back on stronger and stronger treatments. The World Health Organisation has listed antibiotics as a major upcoming health crisis. Meanwhile, people are looking around for other ways to fight disease.

One of those ways is to infect the disease-causing bacteria with diseases themselves.

“Phage therapy” is not a new idea. In fact, it was around before the first antibiotic was even discovered.

Phages are a kind of virus with a capsule attached. But those viruses don’t infect humans: they infect bacteria. So when people are down with a bacterial attack, they can add some phages to make the attacking bacteria ill. It’s the same smallpox trick, with bacteria this time. Phages keep spreading on their own till all the bacteria are down — and then, because there’s no-one left to infect, they die out too.

So if phages are so convenient, why aren’t they more widely used? One reason is that, when antibiotics were discovered, they took over the market. At the time people didn’t know much about viruses and DNA — and antibiotics were poison, pure and simple.

Phages are also very picky about the bacteria they target. A cholera phage won’t work for a typhus bacterium. What’s more, a Russian anti-E.coli phage won’t work for a Mexican or Bangladeshi E.coli. (They tried it. It didn’t work).

Phages, it turns out, are specialised to only work on local species.

So where do you find these specific phages? Actually they could be anywhere: in rivers, sewers, or garbage dumps. But it so turns out that some places have a very good supply. The Ganga river is one of those places.

The Ganga flows out from the Gangotri glacier in the Himalayas. This area, it turns out, used to be deep under the ocean. It was only later that the Indian subcontinent bumped into the rest of Asia, pushing the ground up, up, to form the Himalayas.

Today, the waters flowing from the Gangotri are filled with phages. Scientist suspect they could be phages from long ago, trapped in the icy glaciers, and slowly coming out as they melt. Of course, that can’t be the full story, because many of the phages work well on bacteria living today.

Nowadays there are many rules and regulations about medicine. There have to be, to keep it safe. However, that also means new things, like phage therapy, take time to get accepted.

That’s true in Russia too. But phage therapy is very commonly used over there.

That’s because antibiotics were first discovered in Europe, at the height of the Cold War. Western Europe and the US were in fierce competition with Russia, and the two sides weren’t sharing any information with each other. One of those pieces of information was antibiotics.

So while Europe switched to antibiotics, Russia and its allies continued with phages, developing the technique and keeping it alive till today. With the new problem of antibiotic resistance, phages are suddenly interesting again.

But can’t bacteria become resistant to phages too? Yes, they can — and will. That’s why, people won’t use every phage that works. They plan to select phages with a certain property. When bacteria learn to counter those phages, they’ll face a side-effect: less antibiotic resistant. Bacteria can resist one or the other, but not both.

There are still many things to sort and figure out. There are also new dangers, like ‘what if phages start to attack the bacteria belonging to your own body?’ Right now, some phages are used to — yes — preserve food. But it’ll take a while before phage therapy goes mainstream.

But till then: if you’re under attack by deadly bacteria, and all the medicines are failing, then a dip in the holy Ganga might just do the trick.

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