Читать книгу The Greatest Benefit to Mankind: A Medical History of Humanity - Roy Porter - Страница 11

Some diseases, however, were not so readily coped with: those caused by the zoonoses (animal diseases transmissible to man) which menaced once civilization developed. By 3000 BC cities like Babylon, with populations of scores of thousands, were rising in Mesopotamia and Egypt, in the Indus Valley and on the Yellow River, and later in Mesoamerica. In the Old World, such settlements often maintained huge cattle herds, from which lethal pathogens, including smallpox, spread to humans, while originally zoonostic conditions – diphtheria, influenza, chickenpox, mumps – and other illnesses also had a devastating impact. Unlike malaria, these needed no carriers; being directly contagious, they spread readily and rapidly.

The era of epidemics began. And though some immunity would develop amongst the afflicted populations, the incessant outreach of civilization meant that merchants, mariners and marauders would inevitably bridge pathogen pools, spilling diseases onto virgin susceptibles. One nation’s familiar ‘tamed’ disease would be another’s plague, as trade, travel and war detonated pathological explosions.

The immediate consequence of the invasion of a town by smallpox or another infection was a fulminating epidemic and subsequent decimation. Population recovery would then get under way, only for survivors’ heirs to be blitzed by the same or a different pestilence, and yet another, in tide upon tide. Settlements big enough to host such contagions might shrink to become too tiny. With almost everybody slain or immune, the pestilences would withdraw, victims of their own success, moving on to storm other virgin populations, like raiders seeking fresh spoils. New diseases thus operated as brutal Malthusian checks, sometimes shaping the destinies of nations.

Cities assumed a decisive epidemiological role, being magnets for pathogens no less than people. Until the nineteenth century, towns were so insanitary that their populations never replaced themselves by reproduction, multiplying only thanks to the influx of rural surpluses who were tragically infection-prone. In this challenge and response process, sturdy urban survivors turned into an immunological elite – a virulently infectious swarm perilous to less seasoned incomers, confirming the notoriety of towns as death-traps.

The Old Testament records the epidemics the Lord hurled upon the Egypt of the pharaohs, and from Greek times historians noted their melancholy toll. The Peloponnesian War of 431 to 404 BC, the ‘world war’ between Athens and Sparta, spotlights the traffic in pestilence that came with civilization. Before that war the Greeks had suffered from malaria and probably tuberculosis, diphtheria and influenza, but they had been spared truly calamitous plagues. Reputedly beginning in Africa and spreading to Persia, an unknown epidemic hit Greece in 430 BC, and its impact on Athens was portrayed by Thucydides (460 – after 404 BC). Victims were poleaxed by headaches, coughing, vomiting, chest pains and convulsions. Their bodies became reddish or livid, with blisters and ulcers; the malady often descended into the bowels before death spared sufferers further misery. The Greek historian thought it killed a quarter of the Athenian troops, persisting on the mainland for a further four years and annihilating a similar proportion of the population.

What was it? Smallpox, plague, measles, typhus, ergotism and even syphilis have been proposed in a parlour game played by epidemiologists. Whatever it was, by killing or immunizing them, it destroyed the Greeks’ ability to host it and, proving too virulent for its own good, the disease disappeared. With it passed the great age of Athens. Most early nations probably experienced such disasters, but Greece alone had a Thucydides to record it.

Epidemics worsened with the rise of Rome. With victories in Macedonia and Greece (146 BC), Persia (64 BC) and finally Egypt (30 BC), the Roman legions vanquished much of the known world, but deadly pathogens were thus given free passage around the empire, spreading to the Eternal City itself. The first serious outbreak, the so-called Antonine plague (probably smallpox which had smouldered in Africa or Asia before being brought back from the Near East by Roman troops) slew a quarter of the inhabitants in stricken areas between AD 165 and 180, some five million people in all. A second, between AD 211 and 266, reportedly destroyed some 5,000 a day in Rome at its height, while scourging the countryside as well. The virulence was immense because populations had no resistance. Smallpox and measles had joined the Mediterranean epidemiological melting-pot, alongside the endemic malaria.

Wherever it struck a virgin population, measles too proved lethal. There are some recent and well-documented instances of such strikes. In his Observations Made During the Epidemic of Measles on the Faroe Islands in the Year 1846, Peter Panum (1820–85) reported how measles had attacked about 6,100 out of 7,864 inhabitants on a remote island which had been completely free of the disease for sixty-five years. In the nineteenth century, high mortality was also reported in measles epidemics occurring in virgin soil populations (‘island laboratories’) in the Pacific Ocean: 40,000 deaths in a population of 150,000 in Hawaii in 1848, 20,000 (perhaps a quarter of the population) on Fiji in 1874.

Improving communications also widened disease basins in the Middle East, the Indian subcontinent, South Asia and the Far East. Take Japan: before AD 552, the archipelago had apparently escaped the epidemics blighting the Chinese mainland. In that year, Buddhist missionaries visited the Japanese court, and shortly afterwards smallpox broke out. In 585 there was a further eruption of either smallpox or measles. Following centuries brought waves of epidemics every three or four years, the most significant being smallpox, measles, influenza, mumps and dysentery.

This alteration of occasional epidemic diseases into endemic ones typical of childhood – it mirrors the domestication of animals – represents a crucial stage in disease ecology. Cities buffeted by lethal epidemics which killed or immunized so many that the pathogens themselves disappeared for lack of hosts, eventually became big enough to house sufficient non-immune individuals to retain the diseases permanently; for this an annual case total of something in the region of 5,000–40,000 may be necessary. Measles, smallpox and chickenpox turned into childhood ailments which affected the young less severely and conferred immunity to future attacks.

The process marks an epidemiological watershed. Through such evolutionary adaptations – epidemic diseases turning endemic – expanding populations accommodated and surmounted certain once-lethal pestilences. Yet they remained exposed to other dire infections, against which humans were to continue immunologically defenceless, because they were essentially diseases not of humans but of animals. One such is bubonic plague, which has struck humans with appalling ferocity whenever populations have been caught up in a disease net involving rats, fleas and the plague bacillus (Yersinia pestis). Diseases like plague, malaria, yellow fever, and others with animal reservoirs are uniquely difficult to control.