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"A Plague From All Our Animals" Professor Roy Porter

Roy Porter was a popular and well regarded historian of medicine.

Chickens are only the latest in a historic line of livestock that have brought us new diseases. The fatal interchange of pestilence between animal and man is the story of civilisation itself.

Firstly it was bad beef leading, say, to Creutzfeldt-Jakob disease in humans. Now, in Hong Kong, they are counting their chickens, which appear to have hatched potentially fatal flu among the people of the former colony. They are slaughtering them by the million.

But the fatal interchange of disease between animal and man, however disastrous in the short term, is the story of civilisation itself. Disease is a social development no less than the medicine that combats it. It is the price we have paid, and are still paying, for development.

In the beginning was the Golden Age. The climate was clement; nature freely bestowed her bounty upon mankind; no lethal predators lurked - the lion lay down with the lamb, and peace reigned. In that blissful long-lost Arcadia, according to the Greek poet Hesiod, life was "without evils, hard toil and grievous disease."

It is more than a myth: our previous ancestors really were free of the pestilences that later ambushed mankind. Their bodies may have been malformed, arthritic and lame - and prey to gangrene, botulism, anthrax and rabies - but lethal epidemics such as smallpox, measles and flu must have been virtually unknown.

This was because they were hunters and gatherers, living in scattered, nomadic groups of perhaps 30 or 40. These small bands did not stay put long enough to gather the filth that attracts disease-spreading insects. Nor did they create the high population densities required by the micro-organisms that cause contagious diseases. Above all, isolated hunter-foragers did not tend cattle and the other tamed animals which made civilisation possible, yet often became catastrophic sources of illness.
Being omnivores, they were probably not malnourished and for tens of thousands of years there was ample territory for dispersal as they migrated out of the original home in Africa into all corners of the Old World, initially to the warm regions of Asia and southern Europe, then farther north into less hospitable climes.

All changed when the ice caps melted at the end of the last ice age about 10,000 to 12,000 years ago. Instead of hunting, Stone Age stalkers were forced to grow their own food and settle in one place. In the fertile crescent of the Middle East, in southeast Asia and in America, land was transformed by new management techniques into a reservoir capable of supporting thousands. Once agriculture took root, numbers went on growing since more could be fed.

But while agriculture rescued people from starvation, it unleashed a fresh danger: disease. Prolific pathogens, once exclusive to animals, were transferred to people, initiating the ceaseless evolutionary adaptations which have led to the current situation in which humans share no fewer than 65 micro-organic diseases with dogs and only slightly fewer with cattle, sheep, goats, pigs, horses and poultry.

Many of the worst human diseases were created by proximity to animals. Cattle provided the pathogen pool with the tuberculosis and viral poxes such as smallpox. Pigs and ducks gave humans their influenzas, while horses brought rhinoviruses and hence the common cold. Measles, which still kills 1m children each year, is the result of rinderpest - canine distemper - jumping between dogs or cattle and humans.

Cats, dogs, ducks, hens, mice, rats and reptiles still carry bacteria like salmonella, causing often fatal human infections; water polluted with animal faeces also spreads polio, cholera, typhoid, viral hepatitis, whooping cough and diphtheria.

Vermin learnt to cohabit with humans, insects spread gastroenteric disorders, and contact with rodents led to diseases such as typhus. Food stored in granaries became infested with insects, bacteria, fungoid toxins and excrement.

Settlement also brought malaria. The conversion of forests into farmland created environments tailor-made for mosquitoes: warm waterholes, furrows and puddles ideal for rapid breeding. (Malaria remains out of control across much of the globe.)

The scales of health tipped unfavourably, with infections worsening and human vitality declining. Although agriculture enabled more mouths to be fed, it brought undue reliance on starchy cereal monocultures such as maize, which is high in calories but low in proteins, vitamins and minerals. It also reduced nutritional levels, which allowed deficiency diseases such as pellagra, marasmus, kwashiorkor and scurvy to make their entry onto the human stage. Stunted people are more vulnerable to infections, and it is a striking comment on "progress" that Neolithic skeletons are typically several inches shorter than their Palaeolithic precursors.

The Greeks explained the coming of pestilences and other troubles by the fable of Pandora's Box. The Bible offered the fall: disguised as a serpent, the devil seduces Eve into tempting Adam to taste the forbidden fruit. By way of punishment, the pair are banished from Eden and disease and death became the human condition.

Things could only get worse. By 3,000 BC, cities such as Babylon, with populations of scores of thousands, were rising in Mesopotamia and in Egypt, in the Indus Valley and on the Yellow River.
Such settlements often maintained huge cattle herds, from which lethal pathogens, including smallpox, spread to humans. Diphtheria, influenza, chickenpox, mumps and other contagious illnesses also had a devastating impact.

The era of epidemics began. And though some immunity would develop among the afflicted populations, the incessant outreach of civilisation meant that merchants, mariners and marauders would inevitably bridge pathogen pools, bringing diseases to "virgin susceptibles". One nation's familiar "tamed" disease would be another's plague as trade, travel and war detonated pathological explosions.

With almost everybody slain or immune, the pestilences would withdraw, victims of their own success, before moving on to storm fresh populations. New diseases operated as brutal Malthusian checks, shaping the destinies of nations. Some historians claim malaria played a part in the decline and fall of the Roman Empire.

Next came a crucial stage in disease ecology. Expanding populations accommodated and surmounted certain, once-lethal pestilences. Measles, smallpox and chickenpox turned into childhood ailments which affected the young less severely and conferred immunity to future attacks.
Yet humans remained immunologically defenceless against diseases such as plague, malaria, yellow fever and others with animal reservoirs, which are uniquely difficult to control.

Bubonic plague is basically a rodent disease. It strikes humans when infected fleas fail to find a living rat and pick a human instead. The flea bites its new host and the bacillus enters the bloodstream. Filtered through the nearest lymph node, it leads to the characteristic swelling (bubo) in the neck, groin or armpit. Bubonic plague rapidly kills about two-thirds of those it infects. There are two other even more fatal forms: septicaemic and, deadliest of all, pneumonic plague, which needs no insect vector and spreads from person to person directly via the breath. The first documented bubonic plague outbreak occurred, predictably enough, in the Roman empire - in Egypt in AD 540; two years later it devastated Constantinople, where panic, disorder and murder reigned in the streets, according to historian Procopius: up to 10,000 people died each day, until their was no place to put the corpses. When this bout of plague ended, 40% of the city's population was dead. The disease went on to massacre up to a quarter of the eastern Mediterranean population before spreading to western Europe and ricocheting around the Mediterranean for the next two centuries.

It was a subsequent plague cycle, however, that had the greatest impact. Towards 1300 the Black Death began to rampage through Asia before sweeping westwards through the Middle East to North Africa and Europe. Between 1346 and 1350, Europe alone lost perhaps 20m to the disease.
Not long ago, medicine's triumph over disease was taken for granted. At the close of the second world war a series of books appeared in Britain under the masthead of the "Conquest series". These included The Conquest of Disease, The Conquest of Pain and The Conquest of Tuberculosis - and they celebrated "the many wonders of contemporary science today". This was before the "wonder" advances introduced after 1950.

A signal event was the world-wide eradication of smallpox in 1977. Yet a conclusive victory over disease should always have seemed naive since that would fly in the face of a key axiom of Darwinian biology: ceaseless evolutionary adaptation. This is something that disease accomplishes far better than humans since it possesses the initiative.

Extract reproduced with permission from
The Greatest Benefit to Mankind: A Medical History of Humanity,
by Roy Porter.
(HarperCollins Publishers Ltd £25).