Ockham's Razor

Science journalist Dr Peter Lavelle from ABC Health Online looks at the history of disease and some of the terrible epidemics that have swept through societies throughout history.

Transcript

This transcript was typed from a recording of the program. The ABC cannot guarantee its complete accuracy because of the possibility of mishearing and occasional difficulty in identifying speakers.

Robyn Williams: What's the point of sex? Sexual intercourse isn't the most likely activity, if you think about it: allowing someone else to get thoroughly involved with your delicate parts, and hoping you'll get them back unharmed when it's all over.

Well sex was invented 380-million years ago at Go Go in Western Australia, according to a fossil-minded friend of mine from the Museum in Victoria. Fish did it first and there's the anatomy to prove it, in a fish actually named after David Attenborough, and the point of inventing sex all those years ago, was to mix our respective genomes so as to stay one or two steps ahead of the germs. We need a double genome and lots of shuffling to keep our immune systems tuned to fight off those clever bacteria and viruses.

Not the most romantic explanation of sex, but that's science for you. And sometimes even then, sex isn't enough. We get plagued. And here to explain and give a warning is Dr Peter Lavelle.

Peter Lavelle: If next time you're waiting at the crossing for the lights to change, you should see a ghostly rider on an emaciated pale green horse, holding a pair of scales in one hand, you should worry. It's most likely Pestilence, one of the Four Horsemen of the Apocalypse. He last appeared 2000 years ago to the Apostle John, as recorded in Chapter Six of the Book of Revelation in the bible. So that makes you pretty special on an otherwise ordinary day. But it's bad news unfortunately, because he and his three fellow associates on horseback - Famine, War and Death - are probably here to announce the end of the world for everybody. And having good health cover makes no difference.

Of course it may never happen. If you're a psychologist, you might argue that the figure of Pestilence is an unconscious projection of our fear of disease, one of the first recorded instances. The ghostly rider was a symbol of deep fears of those terrible epidemics that have come from nowhere and swept through our societies from the beginning of recorded time.

But the fear is real enough, and still with us today and so are the epidemics. Just open a newspaper or switch on the TV.

There's Avian flu, parked in millions of chickens, waiting for a chance to cross over to humans. There's SARS, AIDS, and Ebola. There are tropical diseases spreading north and south now that temperatures are rising. There are antibiotic-resistant germs in our hospitals and our nursing homes. And childhood illnesses we thought we'd seen the last of, making a comeback.

How did it come to this? Why, with all our 21st century science and our technology, haven't we rid ourselves of these terrible diseases?

Once upon a time, we were all single-celled micro-organisms. But there came a time, about a billion years ago, when we went our separate ways. Some stayed as single celled organisms like bacteria and fungi, whereas others divided, developed and specialised into insects, reptiles, birds, mammals and eventually humans.

But we kept in touch, and today the relationship persists. We live mostly in a symbiotic relationship, one of mutual benefit. There are about ten times as many foreign bacterial cells in our bodies than there are human cells, trillions of them in fact, especially in the digestive tract, the mouth, the skin, the nose, and the female urogenital tract, where they do things like helping us digest food and keeping our immune systems actives.

Then there are the troublemakers, the small percentage that does us more harm than good. These are the germs, or to use the technical term, the pathogenic organisms: bacteria, fungi, protozoa, and we put viruses in this category too, even though they're not true cells but bits of DNA and RNA with a protein coat. In their struggle to survive, reproduce and multiply, these micro-organisms harm rather than help us.

Now we don't know exactly what causes a micro-organism to become a germ. From its point of view it's simply exploiting an opportunity to survive and thrive. What better way than to invade our body's ready-made cells, and use the nutrients inside them to fuel their own growth and reproduction? It's the microbial equivalent of Easy Street.

It's not so convenient for us though, we need those cells and body tissues to survive ourselves. So over millions of years we've evolved defence mechanisms to recognise and destroy these pathogenic invaders before they harm us.

And the history of disease through the ages is the fascinating struggle between the germ's efforts to attack us, and our body's efforts at defence.

In each encounter in this never-ending David and Goliath struggle there are several possible outcomes.

One - we recognise the germ, mount a response, and kill it. For good measure, we retain a biological memory of that invader, so the next time we meet, the response is more swift and effective.

Two - the germ overwhelms our defences, it proliferates too quickly for our immune systems to recognise it, and the germ overwhelms and kills us. This is actually a Pyrrhic victory for the germ however, because it dies along with us, before it has a chance to spread.

A better outcome for the germ is somewhere inbetween these two extremes - we survive long enough to give the germ plenty of opportunity to multiply and spread before it kills us. Many of the most dangerous and destructive diseases we know are in this category: HIV, tuberculosis and malaria, for example.

In the short term the germ has the advantage of the element of surprise (especially if it's a new germ that our body doesn't initially recognise). Time tends to favour us, though. Our immune systems, through natural selection, get better at recognising and fighting the germ. So once-deadly plagues gradually die out, like the Black Death, or become much less harmful, like Scarlet Fever today.

Now, for most of human history, there's been another factor in our favour - isolation. In prehistoric times we lived in small groups of hunter-gatherers, so there wasn't enough contact with other humans for a germ to spread far. Insects may have spread some diseases like typhus, more widely. But on the whole early humans were more likely to die of starvation, injury or attack from a predator, than an infectious disease from another human.

But between 6,000 and 8,000 years ago, when we settled down in the great river valleys of India and the Middle East and began to plant crops and raise livestock, the balance changed in favour of the germs.

We began to live much closer together, in much greater numbers, huddled in villages, towns and cities, making it easier for disease to jump from animals to humans, and between humans. As we travelled further afield to trade with other towns and cities, diseases spread along trade routes and infected whole people and continents. It was the beginning of the great epidemics of history.

Thanks to the spread of infectious diseases, despite all the advances of civilisation, average life expectancy never improved much over 30 years of age from the beginnings of civilisation until the beginning of the 20th century.

A big part of the problem was, for most of this time we humans had no idea where these diseases actually came from. Were they punishments from the Gods? Did they come from noxious vapours, bad air? No-one knew.

But then in 1675, a Dutchman named Anton van Leeuwenhoek built the world's first microscope; and a human saw micro-organisms for the first time. For the germs, the jig was up. In the early 1860s French chemist Louis Pasteur invented a way of sterilising food by killing micro-organisms and developed the world's first vaccines for anthrax and rabies. In the 1880s, German physician Robert Koch showed how to prove that a particular disease was caused by a particular miro-organism. The next step was to try and eradicate them. From the 1900s sewers and piped water supplies began to appear in cities and towns. Antibiotics became widely available in the 1940s. Mass immunisation programs began in developed countries in the 1950s and '60s.

Today the killer epidemics of polio, typhoid, cholera, and smallpox are so far in the past that your average G.P. wouldn't recognise them now. So why now are we seeing new killer diseases and the re-emergence of old ones? Just like humans, germs are remarkably resilient and good at adapting to new circumstances. They're quick to exploit an opening and the big shifts taking place on our planet are presenting them with new opportunities.

There are more of us crowded closer together. The earth holds 6.7-billion people - by the end of the century there'll be 9-billion, many without running water, living in crowded conditions - ideal for pathogenic micro-organisms.

They can spread further and faster now, thanks to air travel. A hundred years ago it took six months to a year for a germ to circle the globe. Now it takes 24 hours.

Climate change is allowing tropical germs, often hard for doctors to cure, to reach temperate zones for the first time.

And antibiotics, those magic bullets we rely on so heavily, are getting less and less effective. Bacteria are developing resistance to them; in the past we've managed to develop new drugs or different versions of the old drugs, to overcome resistance, but it's getting harder. Developing a drug is hugely expensive and time consuming. Our big drug companies are finding it harder to make profits from antibiotics than from other drugs, so research into new antibiotics is drying up.

And vaccines have been so successful in eliminating diseases in the developed world, that many people are refusing it. Once-common childhood diseases, thought to have vanished, have reappeared.

Still, humans have one powerful strategic advantage over single-celled organisms - the billions of nerve cells organised into what we call the brain. It's got a proven track record of thinking up new ways to outwit the microscopic invaders.

Our research into microbiology is accelerating - especially in the areas of genetic research and genetic engineering.

We've mapped the DNA of many microbes, and scientists in the US, in a huge research program called the Human Microbiome Project, are using this information to increase our knowledge of how microbes cause disease and the part they play in our health.

Scientists like Craig Venter have managed to assemble the entire DNA of microbes in the lab from smaller bits of its constituent DNA. They hope to insert genes into bacteria that will turn them into microscopic factories, producing a host of useful materials; like foods, fuels, even vaccines and antibiotics.

But what if germs themselves benefit from these technological advances?

In the interests of research, we've managed to recreate, in a lab in Atlanta, Georgia in the US, one of the deadliest pathogens in our history, the 1919 Spanish flu virus that killed up to 40-million people worldwide. Suppose it escaped from its fortified lab?

Or what if a lunatic or terrorist created a totally new germ, more deadly and faster spreading even than the Spanish flu, and infected everybody on the planet?

Relax. It will probably never happen. And even if it does, we're better placed to cope with an epidemic than at any time in our history. After all, we're healthier, better fed, with better access to vaccines and drugs than we were, say, 2,000 years ago when the Book of Revelation was written.

All the same, if you should see a ghostly rider on a pale green horse crossing the street outside your house, it's probably best to stay indoors.

Robyn Williams: Or try sobering up. Peter Lavelle is at ABC Health Online. Charles Darwin didn't know about genes, though he was well aware of the way germs could evolve and adapt to catch new hosts. His great historic book about all that came out nearly 150 years ago, in 1859. So what else took place in that amazing year? Next time Peter Mcinnis reminds us of the science in 1859 that got overshadowed by Mr Darwin.

I'm Robyn Williams.

Guests

Dr Peter Lavelle
Science Journalist
ABC Health Online
Sydney

Presenter

Robyn Williams

Producer

Brigitte Seega