Sunday, 11 March 2007

25. Why are we diseased?

The world, including the human body, is full of tiny organisms. When there are either too many or too few of them they can be harmful to humans. These include those without life such as viruses and prions, as well as the vast array of bacteria and similar living micro-organisms.

Some diseases are with us all the time, others suddenly sweep across the population. Endemic diseases, such as malaria, dysentery, leprosy or the common cold are present all the time. Epidemic diseases, such as influenza, measles, cholera and plague, burst out suddenly for a few months or years, then usually subside when their hosts have been destroyed.

There are four main ways in which major diseases spread. There are bacterial diseases which are carried into the body through the mouth, in contaminated food and drink. The various forms of dysentery, typhoid and cholera are examples. If we are to understand how these types of disease change over time, we need to look at human eating, drinking and cooking patterns and the ways in which human and other excrement is dealt with. A change such as eating a new foodstuff or installing a new sewage system can change the pattern of these diseases.

Then there are the vector-borne diseases which are ‘injected’ into parts of the human body by fleas, lice, mosquitoes, snails, flies and other insects. Major diseases are plague, typhus and malaria. These are affected by housing, clothing, footwear and bodily hygiene.

There are also diseases which spread through bodily contact. They include leprosy, venereal diseases and various skin and eye diseases. A new one is AIDS.

There are air-borne diseases, viruses that travel short distances when people cough or sneeze or just breathe; smallpox, measles, tuberculosis and influenza. These are very difficult to protect against, as are a number of other diseases whose causes are little understood, such as various forms of cancer.

Why do diseases become more deadly?

Early successes in increasing human resources in the past led to denser populations in large cities and a congested countryside. This would provide sufficient population density for viral infections such as influenza, smallpox or measles to be sustained and spread. It would also lead to the increased dirt and pollution of water supplies which would raise the levels of diseases such as cholera, typhoid and dysentery.

When war or famine occurred, the final death toll would largely be accounted for by the deaths from disease afflicting a weakened population. As the population built up, cities and towns would become slaughter-houses, gobbling up immigrants who died of the diseases of crowding.

Until very recently this seemed an inevitable tendency. Human populations could only reach a certain density before automatically creating a situation where numbers were cut back again by one disease or another. The rise and fall of ancient civilizations, as well as the collapse or stationary state of many European and Asiatic societies at various times in the last thousand years, can be accounted for by the ravages of disease. No escape from this pattern seemed possible.

Did we have to wait for modern medicine?

Many aspects of the history of the rise and fall of diseases up to the present are still a mystery, but one or two things are plain. There seems to be a dramatic improvement in health in England from about the middle of the eighteenth century. One feature of this was the disappearance of recurring bouts of plague.

By 1750 it seemed clear that both in England and western Europe as a whole plague had disappeared bringing an end to constant anxiety about this horrific disease. Yet no one really knows why plague suddenly vanished within about ten years after 1665.

The fact that bubonic plague vanished within a few years over all of western Europe suggests that the disappearance cannot have been caused primarily by a change in the type of rat (black to brown) which in any case occurred fifty years after the decline. Nor is it possible that all over Europe there was a dramatic change within a few years in the nature of the fleas or the bacillus, housing conditions, standards of living, clothing, climate or any of the other reasons usually put forward.

Some of these may have helped. Yet the only plausible pan-European explanation is that the periodic entry of plague through shipping from Turkey, was prevented by quarantining ships when they arrived in west European ports.

Another significant change in England was the rapid decline of malaria. It was noted that in 1700 about one in twenty of the London population died of malaria. By 1800 malaria was unknown as a cause of death in the city. The previously heavily malarial regions of East Anglia and the Kentish and Sussex marshes were no longer centres of danger.

Again we do not really know why this happened. The explanation that it was due to improved drainage, better houses, or changes in animal husbandry is not convincing. All that is certain is that while southern Europe and particularly Italy were becoming more malarial, England became almost free of this disease in the eighteenth century.

A third change concerned smallpox. Smallpox did not disappear, and there is much argument about whether early vaccination had any positive effect. But it certainly infected and killed different people. By the 1750’s smallpox mainly affected children and in many cases did not kill them.

Why did fewer babies die?

Dysentery, along with malaria, is the greatest killer in history. One of the main ways harmful micro-organisms enter the human body is through the mouth, particularly in the two to four pints of liquid which every human has to absorb daily in order to stay alive. A couple of pints of liquid could contain enough dysentery bacteria to kill the inhabitants of a small city. Almost all liquids which humans drank in the past, particularly milk and water, were contaminated.

People with dysentery evacuate the micro-organisms in their faeces, these then pass onto hands and clothing and, in particular, enter the water supply. Others become infected. At least half the infant deaths in most societies in the past were caused by infant diarrhoea which de-hydrates the body.

As a population grows denser it will pollute the water supplies with human excrement. London, a city which had grown hugely in the eighteenth century, was a classic example and dysentery rates should have been soaring as it grew in size. Yet from about the 1740’s there had been a reversal of this trend. Mortality from dysentery had risen until nearly the middle of the century and then, suddenly started to fall. This meant that the largest city on earth enjoyed relatively low rates of infant and adult dysentery. This was one of the greatest reversals in human history. How had it been achieved?

Again we do not know for certain. All that we do know is that all the conventional explanations, that it was due to improvements in medical knowledge, in hospitals, in the treatment of disease, or changes in the nature of bacteria, in the food supply, in public sanitation and hygiene and in housing are unsatisfactory. Many of them did not occur at all. Those that did were not powerful enough to explain the change.

What did people drink?

What we need to do in solving the problem of this escape from the dysentery trap is to ask what the English were drinking from the 1740’s. If they had been drinking water, then a rise in dysentery (in the absence of water purification and proper sanitation) would have been the result. In fact the majority of the people did not drink water. In England the normal drink had become tea.

Tea became the staple drink of the English in the middle of the eighteenth century. The boiling of the water to make tea killed many of the dangerous amoebae and bacteria. Furthermore, the tea contained a substance called tannin (phenolics) which is one of the most powerful anti-bacterial agents known to man. Typhoid, cholera and dysentery bacilli when placed in even a cold cup of tea will be destroyed within a few hours. When people drink tea they wash out their mouths and stomachs, ingesting not only a sterile liquid (because of the boiling) but also a powerful anti-septic.

The Japanese, and before them for some centuries the Chinese, had benefited from this. The British began to enjoy the healthful effects of tea from the middle of the eighteenth century. It was largely an accidental benefit, for tea was mainly drunk for its taste and invigorating effects. Yet the accident led to the escape from one of the apparently unavoidable death traps. Even infants, drinking the phenolic-infused milk of their mothers, benefited from the practice.

What other reasons are there for the decline of disease?

England did not suffer from any successful large scale foreign invasions for almost a thousand years. It did not endure totally devastating civil wars. Famine and food shortage were less severe than in most agricultural societies. The standard of living for the majority of the population was well above subsistence level. This meant that many people in England in the past, at least compared to rural workers in many civilizations were relatively well fed, clothed, housed and did not overstrain their bodies in manual labour.

Thus, through a set of interconnected, and often accidental, features, the normal tendency to more sickness as population grows was temporarily avoided. This was not through a triumph of medical science or the accident of bacteriological or climatic change. It seems largely to have been the side effect of social, economic and political institutions which had created an unusually stable, modestly affluent, and well regulated population.

The English could still be subject to new diseases, for example cholera and influenza, just as we are subject to AIDS today. Yet England was starting to escape from an almost universal path. This path had always in the past meant that the efficiencies created by a larger number of people living close together in cities and small towns led to a health disaster.

The modern rise in population transformed a sickly, war-ridden, famine-prone world of half a billion into our present situation. In theory, it is possible for twelve times that number to live in relative peace and plenty (though perhaps only half of the world’s population actually do so). This was unimaginable in 1750. Yet it has happened. The first phase of this had occurred in England by 1800. The second would follow from the later nineteenth century when a true understanding of micro-organisms and effective treatments for many of the major killers were developed.

Yet the story is far from over. The spread of many new diseases (AIDS, SARS, MRSA), the return of old ones (malaria, tuberculosis) and the growing resistance to antibiotics reveals the continuing struggle between species. Humans are predators on many other species. They are also an easy prey for the microbes.

There is still enormous suffering from disease. Better food, better water supplies and better sewage systems, which could be installed throughout the world for a tenth of the cost of current production of weapons of war, would halve the rates of many types of illness. An observer from another planet might be puzzled. As a species we prefer to put our resources into threatening and killing each other rather than devoting our attention to alleviating the pain which blights millions of people in their disease-soaked lives.

No comments: