changing equations

The very microbes that helped humans evolve now make us sick

Our bodies have not changes as much as the standard for what constitutes a good microbe versus a bad one.

Between the mid-1990s and the mid-2000s alone, the likelihood of having a classmate with a food allergy increased by 20 per cent in the United States. In fact, over the past five decades, the incidence of all allergies and autoimmune diseases – caused by your body attacking itself – has skyrocketed. What could explain our sudden hypersensitivity to our surroundings and ourselves? Since evolution operates on the timescale of millennia, the culprits lie not in our genes but somewhere within our environment.

One thing that has changed in public health is our awareness of germs and how they spread. In response to that insight, over the past half-century our implementation of hygiene practices has spared us from debilitating infections and enormous human misery. But the new vigilance might have altered the development of our immune system, the collection of organs that fight infections and internal threats to our health.

The idea that too clean an environment might be harmful has been dubbed “the hygiene hypothesis”. The concept has been perverted by some to suggest that the less clean the environment, the better. But its meaning is different: it is not dirt that we are missing but exposure to certain microbes that normally contribute to the development of our immune system. “It’s not that we aren’t exposed enough to microbes but that we’re not exposed to the right types of microbes,” says the immunobiologist Ruslan Medzhitov at the Yale School of Medicine, also head of the Food Allergy Science Initiative at the Broad Institute.

So what has changed? In short, it’s the standard for what constitutes a good microbe versus a bad one. “Take bacterial species that increase nutrient absorption from food,” Medzhitov says. These were immensely beneficial at a time where you had to go days without eating. Today in the parts of the world with an overabundance of food, having such bacteria in your intestine contributes to obesity. “Microbes that cause intestinal inflammation are another example of what we call bad microbes because they induce [detrimental immune] responses. But in the past, these microbes could have protected you from intestinal pathogens,” he adds.

The most common such foes are helminths, commonly known as intestinal worms. While they have been eradicated in most of the economic West, their absence from our environment might be contributing to the increase in allergic and autoimmune diseases by diverting our immune system’s attention towards our food and ourselves. This is what Ken Cadwell, a microbiologist at New York University, contends. He is interested in better understanding Crohn’s, an autoimmune disease caused by our immune system attacking our gastrointestinal tract.

Worm treatment

Cadwell’s team discovered that the bacterium Bacteroides vulgatus causes reduced mucus secretion in mice, something that results in the condition. In collaboration with the parasitologist P’ng Loke, also at NYU, Cadwell then decided to treat mice that had Crohn’s disease with helminths, known to trigger mucus secretions in the intestine. And it worked! The two researchers identified that the ensuing establishment of Clostridiales bacteria in the gut cured the mice.

But would it work in humans? Loke collected stool samples from populations living in helminth-endemic areas in Malaysia before and after deworming treatment, and he noticed something intriguing. People from these regions had abundant Clostridiales in their gut before treatment and a lower incidence of autoimmune bowel diseases. After successful deworming, the protective bacteria disappeared, setting the stage for autoimmune illness to rear its head.

Yet treating humans with worms will not work as a public-health measure. Worm treatment is beneficial only for those Crohn’s patients with a genetic make-up causing reduced mucus-secretion and lacking Clostridiales bacteria. For everybody else, it is just a harmful infection. Now scientists are trying to better understand how to reap the benefits of worm therapy while avoiding its downsides. “I am more in favour of an alternative that gives the same [health] effect without having to give somebody a live parasite,” says Cadwell. “That would be ideal.”

Besides the change in our exposure to microbes, our modern lives include diets much higher in sugar, salt and carbs. Now a team from Harvard and Yale has discovered that even moderate increases in salt consumption trigger activation of immune actors, known as Th17 cells, especially prevalent in such autoimmune diseases as arthritis and multiple sclerosis, to name just two. “Recent studies found that if you have the right [genes], your likelihood of developing rheumatoid arthritis goes up 10-fold from the average risk in the population. But if you combine that with smoking, it leads to an increased risk of 100-fold. Now a recent study also showed that if you have the right [genes], you smoke, but you also consume a high-salt diet, the risk goes up 500-fold,” says the immunologist Vijay Kuchroo at Harvard, who did the work with his colleague, the neurologist David Hafler of Yale.

We are forced to conclude that the explosion of allergies and autoimmune diseases results from a mismatch between genes selected by pressures of our evolutionary past and the reality of modern life. While we have adapted in the past, we might not be able to adapt again by relying on biology alone. There is no going back – the old world is gone. To curtail the increase in allergies and autoimmunity, we have to evolve our social, political and scientific regimes, providing healthier food options at lower cost and improving our understanding of the underlying immunological mechanisms at play.

The writer is a graduate student in immunology at the Iwasaki Lab at the Yale School of Medicine.

This article was first published on Aeon.

We welcome your comments at letters@scroll.in.
Sponsored Content  BY 

Some of the worst decisions made in history

From the boardroom to the battlefield, bad decisions have been a recipe for disaster

On New Year’s Day, 1962, Dick Rowe, the official talent scout for Decca Records, went to office, little realising that this was to become one of the most notorious days in music history. He and producer Mike Smith had to audition bands and decide if any were good enough to be signed on to the record label. At 11:00 am, either Rowe or Smith, history is not sure who, listened a group of 4 boys who had driven for over 10 hours through a snowstorm from Liverpool, play 15 songs. After a long day spent listening to other bands, the Rowe-Smith duo signed on a local group that would be more cost effective. The band they rejected went on to become one of the greatest acts in musical history – The Beatles. However, in 1962, they were allegedly dismissed with the statement “Guitar groups are on the way out”.

Source: Wikimedia Commons
Source: Wikimedia Commons

Decca’s decision is a classic example of deciding based on biases and poor information. History is full of examples of poor decisions that have had far reaching and often disastrous consequences.

In the world of business, where decisions are usually made after much analysis, bad decisions have wiped out successful giants. Take the example of Kodak – a company that made a devastating wrong decision despite overwhelming evidence to the contrary. Everyone knows that Kodak couldn’t survive as digital photography replaced film. What is so ironic that Alanis Morissette could have sung about it, is that the digital camera was first invented by an engineer at Kodak as early as 1975. In 1981, an extensive study commissioned by Kodak showed that digital was likely to replace Kodak’s film camera business in about 10 years. Astonishingly, Kodak did not use this time to capitalise on their invention of digital cameras – rather they focused on making their film cameras even better. In 1996, they released a combined camera – the Advantix, which let users preview their shots digitally to decide which ones to print. Quite understandably, no one wanted to spend on printing when they could view, store and share photos digitally. The Advantix failed, but the company’s unwillingness to shift focus to digital technology continued. Kodak went from a 90% market share in US camera sales in 1976 to less than 10% in 2012, when it filed for bankruptcy. It sold off many of its biggest businesses and patents and is now a shell of its former self.

Source: Wikimedia Commons
Source: Wikimedia Commons

Few military blunders are as monumental as Napoleon’s decision to invade Russia. The military genius had conquered most of modern day Europe. However, Britain remained out of his grasp and so, he imposed a trade blockade against the island nation. But the Russia’s Czar Alexander I refused to comply due to its effect on Russian trade. To teach the Russians a lesson, Napolean assembled his Grand Armée – one of the largest forces to ever march on war. Estimates put it between 450,000 to 680,000 soldiers. Napoleon had been so successful because his army could live off the land i.e. forage and scavenge extensively to survive. This was successful in agriculture-rich and densely populated central Europe. The vast, barren lands of Russia were a different story altogether. The Russian army kept retreating further and further inland burning crops, cities and other resources in their wake to keep these from falling into French hands. A game of cat and mouse ensued with the French losing soldiers to disease, starvation and exhaustion. The first standoff between armies was the bloody Battle of Borodino which resulted in almost 70,000 casualties. Seven days later Napoleon marched into a Moscow that was a mere shell, burned and stripped of any supplies. No Russian delegation came to formally surrender. Faced with no provisions, diminished troops and a Russian force that refused to play by the rules, Napolean began the long retreat, back to France. His miseries hadn’t ended - his troops were attacked by fresh Russian forces and had to deal with the onset of an early winter. According to some, only 22,000 French troops made it back to France after the disastrous campaign.

Source: Wikimedia Commons
Source: Wikimedia Commons

When it comes to sports, few long time Indian cricket fans can remember the AustralAsia Cup final of 1986 without wincing. The stakes were extremely high – Pakistan had never won a major cricket tournament, the atmosphere at the Sharjah stadium was electric, the India-Pakistan rivalry at its height. Pakistan had one wicket in hand, with four runs required off one ball. And then the unthinkable happened – Chetan Sharma decided to bowl a Yorker. This is an extremely difficult ball to bowl, many of the best bowlers shy away from it especially in high pressure situations. A badly timed Yorker can morph into a full toss ball that can be easily played by the batsman. For Sharma who was then just 18 years old, this was an ambitious plan that went wrong. The ball emerged as a low full toss which Miandad smashed for a six, taking Pakistan to victory. Almost 30 years later, this ball is still the first thing Chetan Sharma is asked about when anyone meets him.

So, what leads to bad decisions? While these examples show the role of personal biases, inertia, imperfect information and overconfidence, bad advice can also lead to bad decisions. One of the worst things you can do when making an important decision is to make it on instinct or merely on someone’s suggestion, without arming yourself with the right information. That’s why Aegon Life puts the power in your hands, so you have all you need when choosing something as important as life insurance. The Aegon Life portal has enough information to help someone unfamiliar with insurance become an expert. So empower yourself with information today and avoid decisions based on bad advice. For more information on the iDecide campaign, see here.

Play

This article was produced on behalf of Aegon Life by the Scroll.in marketing team and not by the Scroll.in editorial staff.