HEALTH AND DISEASE

Kenneth F. Kiple

Studies centered on political, economic, military, or church affairs are very old avenues of historical investigation in Europe. By considerable contrast the study of disease and history is quite new.

In part this is because until the beginning of germ theory in the late 1800s, people did not know what caused them to be sick and to die. When court chroniclers and historians felt pressed to account for the presence of diseases, "God's will" was a handy explanation—a "will" that was routinely credited with epidemics that delivered misery and death to thousands, even hundreds of thousands, of individuals. Perhaps because God might be credited but never blamed, this explanation was also generally laden with the suspicion that divine will had gotten a helping hand from secular sources such as the ragged and dirty poor, or outsiders, or Jews, all of whom came to comprise the usual scapegoats during epidemics.

However, the study of disease in history is also a phenomenon of the last two centuries or so because the writing of history was an enterprise that tended to deal with the affairs of a highly visible elite as opposed to the murky masses. Hence epidemics—the most dramatic manifestation of disease—which as a rule fed on those masses while sparing the elite (whose wealth separated them physically and nutritionally from the masses and permitted flight from epidemic sites), were often not counted as very noteworthy events for those in a position to record them.

It was the birth of both germ theory and social history that changed this state of historiographical affairs by clearing the way for twentieth-century historians to focus on the role of human health in history. These historians, in turn, have made the study of the impact of disease on societies indispensable to any holistic understanding of those societies. This article looks at the march of a number of diseases across Europe from the Renaissance to the present. It attempts to do so in chronological order, but sections of the article sometimes overlap because an effort has also been made to present diseases in categories. Most of these categories feature diseases of an epidemic or pandemic nature. However, the less dramatic endemic diseases are also discussed, as are those caused by foods and nutritional deficiencies.

As for nomenclature, "epidemic" is defined as a disease suddenly appearing to attack many people in the same region at roughly the same time and "pandemic" as an epidemic disease that becomes widely distributed throughout a region, continent, or the globe; "endemic" refers to a disease that is always present in a population.

DISEASE AND THE RENAISSANCE

Somewhat ironically, given its connotation of "rebirth," a distinctive feature of the Renaissance was widespread death, much of it caused by bubonic plague, which had become pandemic. It is generally said (but not without dispute) that the disease originated east of the Caspian Sea, then followed the caravan routes westward to burst upon Europe in 1347–1348, just as the Mediterranean Renaissance was getting under way. The disease, however, apparently failed to establish an endemic focus in Europe, meaning that it had to be reintroduced if Europe was to experience another epidemic; indeed it was reintroduced with an awful regularity, reappearing somewhere every quarter of a century or so until 1720—almost four hundred years of plague that began in the Renaissance and ceased only in the modern period.

The initial wave of plague, which we call the Black Death, lasted a terrible seven years, beginning with its appearance in Sicily in 1347. It subsequently reached the Italian peninsula, then marched through the Iberian Peninsula in the summer of 1348 and northward to reach Paris and the ports of southern England. The following year saw the British Isles devastated; then plague plunged into northern Europe and by 1350 was moving through eastern Europe. This first European tour of the plague culminated with an assault on Russia that saw Moscow under siege in 1353.

Although its trajectory was such that no region suffered plague for more than a few months, historians generally agree that the mortality it inflicted was in the 20 to 50 percent range. In the Mediterranean, in urban areas where people lived in close proximity to one another, such as Florence, Venice, Rome, Milan, and Barcelona (which were nurturing the early Renaissance), mortality rates were probably the highest. But it was in the myriad towns, villages, and hamlets, which contained the vast bulk of the population of a Europe still lingering in the late Middle Ages, that the plague harvested the overwhelming majority of its victims.

The impact of the Black Death, combined with that of the recurrent plague epidemics that followed, is difficult to comprehend in both breadth and magnitude. Populations that had been enjoying a period of sustained population growth were drastically pruned practically overnight, and a Europe that had been relatively crowded was so no longer. Whole villages were empty and fields deserted save for equally deserted sheep, cattle, and hogs. A great shortage of labor meant that patterns of landholding and land use had to change. Although not always without strife, landlords became easier to deal with, and many peasants became landowners. Population pressure on food supplies was reduced, and prices fell because of a lack of demand. Animal protein—suddenly abundant—began to grace even the tables of the poor, and the pace of urbanization quickened as individuals no longer needed in the countryside found nonagricultural jobs in cities and towns.

In addition to these significant changes, the onset of plague seems to have wrought some curious microparasitic alterations in Europe's disease ecology beyond the obvious introduction of the rodent disease Yersinia pestis, which we call bubonic plague. For reasons not fully understood, leprosy—a disease present in Europe since at least the sixth century—went into an abrupt recession while, at the same time, pulmonary tuberculosis began an ever increasingly prosperous career that would elevate it to the status of a major plague by the eighteenth century. One explanation offered by the American historian William McNeill for the decline of leprosy at this time takes note of the fact that the arrival of plague coincided with climatic change that saw average temperatures falling precipitously in Europe. Prior to the Black Death, with most of Europe put to the plow, firewood was scarce, and people doubtless kept warm on cold nights by huddling together, thereby increasing the ability of leprosy to spread. But in the wake of the Black Death there would have been less need to huddle, with some 40 percent fewer individuals putting pressure on the firewood supply; such a population reduction also meant that wool (and hence clothing) was more readily available. All of these factors may have acted in concert to interrupt leprosy's pattern of skin-to-skin transmission. As for the rise of tuberculosis (TB), the growth of crowded urban areas encouraged by the plague would have proven a fine incubator for this illness, which most frequently spreads from person to person by infected droplets from the lungs.

Populations did begin to recover with the improved conditions of life ushered in by the plague, and despite renewed appearances of this disease, urban areas did grow to support still other illnesses. Indeed, although it is difficult for historians to put a name to most epidemic diseases prior to the sixteenth century, there is no question that their pathogens were ricocheting about inside the walls of the swelling cities and towns, whose rivers and wells festered with human waste, whose markets swarmed with flies, whose dwellings were alive with rodents, and whose human inhabitants avoided bathing and seldom changed woolen clothing and bedding even though they harbored lice, bedbugs, and other assorted vermin.

EPIDEMIC DISEASE DURING THE EXPANSION OF EUROPE

While Europeans were cultivating pathogens at home, they were also importing them from abroad. The Crusaders have been suspected of returning home with some novel microorganisms as well as exciting new plants and an enhanced weltanschauung, but it was the Portuguese, in leading the expansion of Europe with their century of African exploration, who brought many in Europe into contact with tropical ailments for the first time. Yaws—a disease caused by treponemas, a genus of spirochetes—may or may not have been present in an earlier and warmer Europe, but the illness began regularly reaching Iberia via a Portuguese–run slave trade and, according to epidemiologist E. H. Hudson, could have evolved into the syphilis that would soon engulf the Continent.

Falciparum malaria was another African contribution to Europe's pool of pathogens. Europeans had suffered from other types of malaria that were widespread during the Middle Ages; but falciparum malaria is by far the most lethal of the malarial types, so deadly in fact that it summons genetic defenses against it through the process of natural selection—defenses such as the sickle-cell trait and blood enzyme deficiencies that hold down the level of parasitization in the human body. The disease had been present in the eastern Mediterranean for thousands of years—long enough to have encouraged the development of such defenses (as discovered by the Crusaders, who did not possess them)—and in some nearby Greek and southern Italian populations as well. But the Iberians had had no opportunity to develop protection against this illness now arriving directly from Africa, which took root in the peninsula and even depopulated the Tagus Valley for a time. Indeed, the extent of that root can be seen in the fact that today, like Italians and Greeks of the Mediterranean, some southern Iberians also carry evidence in their blood of the beginnings of genetic defenses against falciparum malaria.

Meanwhile, typhus is thought to have first reached Europe via Granada in 1489–1490 with Arab reinforcements for those Moors locked in combat with the forces of Ferdinand and Isabella—the final spasm of centuries of a reconquest that saw Spain ultimately triumphant in 1492. Typhus, however, proved a staunch ally of the Moors by killing some seventeen thousand Spanish soldiers—six times more than the Moors themselves managed to dispatch. And this was only the beginning of a series of typhus epidemics erupting on European battlefields throughout the centuries that followed.

It was in the same year that the Moors were defeated by the Catholic monarchs that their emissary Christopher Columbus and his men arrived at the New World. Shortly thereafter syphilis turned up in Naples, where the French and Spanish armies were contesting control of that kingdom. Initially known as the "disease of Naples," syphilis burned with such a fury among the French forces—ecumenically recruited from all corners of Europe—that they were compelled to withdraw, and the disbanded soldiers carried this new pox to all of those corners. It was now called the French disease (by most everybody but the French); yet some took note of the coincidence of its outbreak with the return of Columbus and suggested that it might better be called the Spanish disease.

Many medical historians and bioanthropologists lean toward the view that syphilis was probably a relatively mild New World treponemal infection that became virulent when transferred to the Old World (perhaps by fusing with other treponemas), and thus it was, technically, a new disease for the Europeans. Certainly it seemed like a new disease loosed on a people with little in the way of immunological defenses. It spread with such extraordinary speed that it was reported from all over Europe by 1499; it was also extraordinary in its virulence, producing hideous symptoms and high rates of mortality. Yet a few decades later, syphilis began to relent in its ferocity and to lose its epidemic character, evolving into the relatively mild disease known in the late twentieth century. But it is worth noting that what the disease lost in malignancy it gained in its ability to stigmatize those who contracted it; the syphilitic came to personify vice itself.

In England, however, as the fifteenth century came to a close, people had more in the way of pestilence to contend with than just syphilis. In 1485 a mysterious disease dubbed sudor anglicus, the "sweating sickness," or simply the "Sweat," swept parts of that country and killed up to a third of the populations of the towns and villages it visited. The Sweat made return visits to England (but not Scotland or Ireland) in 1506, 1517, 1528, and finally, 1551. Then it apparently vanished forever, leaving one of the most intriguing mysteries of historical epidemiology in its wake. What was the disease and where did it come from?

The 1485 outbreak took place during the War of the Roses, which changed the status of the victorious Henry Tudor, duke of Richmond, to that of Henry VII, king of England, and it was suspected that the Sweat had entered the country with some of Henry's mercenaries returning from France. But no single factor, including military movement, seems able to account for the other outbreaks. Only once did the Sweat apparently strike outside of England, when in 1528–1529 it was reported as epidemic across northern Europe all the way to Russia. However, in an area also under siege by syphilis and typhus, it is difficult to disentangle Sweat morbidity and mortality from that caused by these other two epidemics (not to mention the myriad other infections afoot). Influenza, malaria, typhus, and streptococcal infection have all been put forward as candidates, and in 1981 the medical historians John Wylie and Leslie Collier proposed that the disease was caused by an arbovirus (any of a group of viruses transmitted to humans by mosquitoes and ticks) harbored by small animals and carried to humans by insects. Since arboviruses are generally tropical in residence, this raises the intriguing (but probably epidemiologically remote) possibility that the close connection of the English with the Portuguese during the years of the Sweat outbreaks had put them in touch with some virus of tropical Africa.

One reason for dismissing typhus and influenza as candidates for the Sweat is that the English, like the rest of the Europeans, had become painfully familiar with both of them and thus were not likely to view them as novel. Beginning in 1522 at Cambridge, typhus had started making courtroom appearances and became the scourge behind the famous Black Assizes. The disease—also known as "jail fever"—was carried by prisoners into the courtroom, where it infected spectators, judges, and jurors.

Typhus made its second great battlefield appearance in 1528—this time in Naples—and became the second disease within thirty-two years in that disputed kingdom to wreck great French plans of state. The troops of the Holy Roman Emperor Charles V, which were under French siege near Naples, had been decimated by bubonic plague to the point where a French victory seemed assured, and all of Italy stood ready to acknowledge the rule of Francis I. But then the power of pestilence suddenly sided with imperial ambition as typhus launched a counterattack that destroyed some thirty thousand soldiers in the French army. Like syphilis before it, typhus engineered a French defeat that opposing troops could not.

Given that bubonic plague was now intermingling with the new plagues of syphilis and typhus, sixteenth-century Europe was a pathogenically perilous enough place without smallpox, an old disease now suddenly acting like a new and virulent one. There were two types of this disease, which medicine believes it finally killed off in the last half of the 1970s. One was variola major (major, because it produced mortality rates of up to 25 to 30 percent); the other was the much milder variola minor, with mortality rates of 1 percent or less. Doubtless, there were strains intermediate between the two, but until the first decades of the sixteenth century, it seems to have been mostly a relatively mild smallpox that Europeans had known. Yet, beginning in that century, smallpox increasingly became one of Europe's biggest killers, so that in the seventeenth and eighteenth centuries it accounted for 10 to 15 percent of all deaths in some countries and as much as 30 percent in some cities.

There is no satisfactory explanation for this mysterious increase in virulence, only intriguing speculation that involves the Americas on the one hand and Africa on the other. Smallpox reached the Caribbean by at least 1518 and was carried onto the American mainland in 1519, where it began a devastating march north and south that brought demographic disaster to Native American populations wherever it appeared. The deadliness of smallpox for them has generally been explained in terms of their lack of experience with the malady and thus their lack of resistance to it. But it is also possible that in this human crucible the smallpox virus became increasingly venomous as it passed through tens, even hundreds, of thousands of inexperienced bodies and was thus transformed into the virulent disease that would soon replace plague as the most important check on European populations.

Alternatively, it could be that the smallpox unleashed on Native Americans was already a killer. It is generally assumed that India was the cradle of smallpox, but long ago August Hirsch, the great German epidemiologist, pinpointed regions of central Africa as other foci. The year 1518, when smallpox entered the Caribbean, was also the year that Charles I of Spain permitted the beginning of the transatlantic slave trade, and it is not impossible that the smallpox that fell on the Native Americans was a malignant disease of Africa rather than the relatively mild one of Europe. Certainly it was the case that later explosive smallpox epidemics appear to have reached the Americas from Africa via the Atlantic slave trade. But either way, as a new strain of smallpox from Africa or a newly mutated disease that had incubated in the New World, this "new" smallpox easily reached the European Old World to settle in there as well.

EUROPEAN ENDEMIC AND FAMILIAR EPIDEMIC AILMENTS

These major plagues were regularly joined by other diseases to prune continental populations. Influenza made sufficiently regular appearances in the fifteenth century to precipitate detailed descriptions of the disease, and three large-scale epidemics ravaged Europe in 1510, 1557–1558, and 1580. The latter was actually a pandemic that made itself felt in Asia and Africa as well, and the high rates of morbidity and mortality it produced among young adults suggests a strain similar to that which caused the world-shaking pandemic of 1918.

Typhoid, which travels the oral-fecal route, generally in water, was obviously widespread in Europe's fouled water supplies, where there was little or no separation of sewage and drinking water. Indeed, because in the absence of effective antibiotic treatment, typhoid (or putrid malignant fever, as it was called) can kill 10 to 20 percent of those it infects, one might wonder why anyone was alive to experience the other diseases under discussion. One ready answer, however, is that exposure to the typhoid bacillus provides a relative immunity to future attacks. Another is that, on the whole, people drank water that had been processed into alcoholic beverages and thus purified. Later they added nonalcoholic beverages to the list, such as coffee, tea, and cocoa—all of which were generally made with boiling water.

Measles, which was often confused with smallpox and frequently operated in concert with it, also struck alone, and numerous measles epidemics were reported in the seventeenth and eighteenth centuries. Scarlet fever, diphtheria, rheumatic fever, and mumps were other diseases to be endured, especially by the young, which brings us to the issue of urbanization and childhood illnesses.

THE DECLINE OF THE OLD EPIDEMICS

Perhaps paradoxically, even though Europe was awash in a sea of pathogens, the continued growth of cities slowly began to stem that pathogenic tide. It is not that cities and towns were healthy places. Quite the contrary, they were, as already described, squalid strongholds of pestilence. But as they grew larger they rendered themselves capable of taming some of that pestilence by transforming epidemic diseases into endemic diseases. Epidemic diseases such as smallpox and measles tended to roll over an area, either killing or immunizing victims as they did so. Then they disappeared because of a lack of suitable hosts and only reappeared when these were again present in the form of a new generation of nonimmune individuals. But as urban populations grew larger, they eventually produced a sufficient number of new hosts through births to retain diseases on a year-round basis and keep them from disappearing, whereupon they became essentially childhood diseases. In other words, pathogens that had periodically slaughtered young and old indiscriminately were now confined mostly to the young. Much life was saved by this arrangement because many diseases tend to treat the young more gently than they do adults while providing them with immunity against a future visitation.

FOODS, NUTRIENTS, AND ILLNESSES

Europeans also suffered from ailments that were food and nutrition related. One was ergotism—a fungal poisoning caused by the ergot fungus, which can form on cereal grains and especially on rye ears to poison heavy consumers of breads and porridge made from affected grains. Needless to say these consumers were usually the poor. August Hirsch listed 130 epidemics of the disease in Europe between 591 and 1879, while acknowledging that these were only a fraction of the ergotism outbreaks that had taken place. Also known as St. Anthony's fire, when the disease affected the central nervous system it was called convulsive. In its other, gangrenous form, the cardiovascular system is affected. Either form could and did kill relentlessly. Data has revealed, for example, that during ten ergotism epidemics in nineteenth-century Russia, those who were afflicted experienced a mean mortality rate of 41.5 percent. But ergotism is also of interest because the convulsive type of the disease causes victims to experience hallucinations and convulsions. Interestingly, research has linked years favorable to the growth of ergot with the hallucinations and convulsions that were a part of religious revivals and even with the "Great Fear" that swept the French countryside in 1789, just prior to the French Revolution.

Europeans also had their share of deficiency diseases. Scurvy, arising from a lack of vitamin C, must have seemed like another new disease as the maritime nations of Europe put together the technology to keep ships away from shore long enough for it to develop. In 1498 Vasco da Gama lost perhaps as many as half of his crew to the affliction, and from that time until about 1800, estimates would have as many as a million sailors dying from scurvy—probably more deaths than were generated by naval warfare, shipwrecks, and all other shipboard illnesses combined. Yet scurvy was not confined to seamen. It tormented the inmates of prisons, workhouses, hospitals—indeed anyone without access to foods containing vitamin C. People living in Europe's northernmost regions, characterized by long winters, in early spring began searching out the first green shoots of those various plants they called "scurvy grass" to heal their bleeding gums. Scurvy was also a regular visitor to battlefields, especially when a siege was under way. But despite the experiments of James Lind, James Cook, and others, which had shown the efficacy of lime juice in preventing or treating the disease, and despite the British navy's making lime juice a part of the rations of its seamen (hence the name "limeys"), scurvy continued to break out among other navies and especially armies, from Napoleon's army during its retreat from Moscow to those forces engaged in the Crimean War, right up to the combatants in the Franco-Prussian War of 1870–1871.

Another deficiency disease, pellagra, arose in northern Spain, Italy, southern France, and the Balkans, where the peasants had planted maize from the Americas and then centered their diets on the grain. Native American populations had lived for millennia on maize but treated it with lime (calcium oxide), which not only made the kernels pliable but broke the chemical bond to release the niacin they contained. Without such processing, a consumer whose diet rests heavily on maize will become niacin deficient and pellagra prone. The disease produces diarrhea to aggravate malnutrition, dermatitis, and dementia, finally resulting in death. In France, where a physician successfully urged his government to curtail maize production and encourage the peasants to cultivate other crops and eat more animal foods, the disease was virtually wiped out by the end of the nineteenth century. Elsewhere, it continued to haunt the poor in maize-growing areas well into the twentieth century.

Rickets occurs when the growing bones of the young (the adult form is called osteomalacia) do not receive sufficient calcium—generally because of a lack of vitamin D, so necessary for the utilization of calcium. The bulk of our vitamin D is the result of bodily production that takes place when the skin is stimulated by the ultraviolet rays of sunlight reflecting from it. Thus, the bowed legs and bossed skulls left in the wake of bouts with rickets were especially prominent in northern Europe and England, which frequently experienced long, overcast winters. In fact, the disease was such a feature on England's medical landscape during the seventeenth century that in 1650 it received what has been called its classic description in the book De rachitide (On rickets) by Francis Glisson. A few years later, in 1669, another physician, John Mayow, followed with his own On Rickets, claiming that the affliction had first appeared in England only around 1620. Whatever the reasons for its abrupt appearance, rickets was not likely to wane as England began the industrialization process, filling the air with coal smoke and smog that screened out the sun's ultraviolet rays and closed off working-class children in urban slums hardly constructed with healthy exposure to sunlight in mind. In 1789 an English physician discussed the efficacy of cod-liver oil in curing and preventing rickets, but another century and a half would elapse before science, in discovering the vitamins, would learn why it was effective.

The year 1789 also effectively marked the end of a curious practice begun half a millennium before, when Louis IX, newly returned from the Crusades, began administering the "king's touch" to cure scrofula. Outward symptoms of scrofula were swellings in the neck. When these swellings were enlarged neck glands that frequently became putrid, they were mostly the result of primary tuberculosis of the cervical lymph nodes caused by the ingestion of milk from tubercular cows. Because most cases of primary tuberculosis resolve themselves over time and the unsightly symptoms disappear, the king's touch must doubtless have seemed miraculous—not only to the king's subjects but also to the monarch himself, through whose hands supposedly passed the healing power of the Almighty.

Not to be outdone, monarchs in England soon followed suit to show that they, too, were ruling by divine right, and the touch was increasingly used and then widely administered by the Stuart kings. Indeed, in 1684 there was such a mob of applicants for the touch that many were reportedly trampled to death in a vain attempt to reach the hand of a restored Charles II. Perhaps the record for touching, however, belongs to Louis XV of France, who reportedly touched more than two thousand individuals at his coronation in 1722.

Scrofula could also mean goiter—an enlargement of the thyroid gland caused by iodine deficiency—and since these cases do not resolve themselves, they would not have been good advertisements for the king's touch. Both England and France seem to have had goiter sufferers, but fortunately for the reputation of the royal touch in the latter country, the real centers of goiter were far from the throne in the remote mountains and valleys with their iodine-leached soils in and around the Alps and the Pyrenees.

MORTALITY AND ITS DECLINE

In the seventeenth century typhus continued to stalk Europe and especially its battlefields so that during the Thirty Years' War (1618–1648) battle casualties were minimal when compared with the ravages of typhus, not to mention those of plague, scurvy, and dysentery. But typhus was also carried to civilian populations: Germany was said to be so devastated in some places that wolves roamed empty streets. Typhus entered Scandinavia during the Baltic wars, was in the thick of the struggle between Crown troops and Huguenots in France, and became a major player in the English civil wars, reportedly converting the island into one huge hospital by 1650.

By this time tuberculosis mortality also had begun to increase considerably in countries undergoing urbanization, such as England, where at midcentury, despite typhus, TB was accounting for some 20 percent of all deaths and London was contributing a disproportionately large percentage of the victims. Perhaps by way of compensation, the Great Plague of London in 1665 marked the final visit of this pestilential scourge to Britain, and by the beginning of the eighteenth century, all of northern Europe was protected by the famous Cordon Sanitaire—the Austrian barrier manned by 100,000 men to keep plague from reaching Europe from the Ottoman lands. To the south, however, plague seemed unrelenting. It besieged Naples in 1656, where it reportedly killed some 300,000 people, and Spain, which had been buffeted by epidemics of plague in 1596–1602 and 1648–1652, continued to suffer from it during the nine long years from 1677 to 1685. Mercifully, however, plague's career also came to a close in the European Mediterranean countries after a last furious parting shot, between 1720 and 1722, that killed tens of thousands in Marseilles and Toulon. Eastern Europe and Russia were the last areas of the Continent to become plague free, following severe epidemics in Kiev in 1770 and Moscow in 1771.

Prior to the nineteenth century, medicine was powerless against plague and other epidemic pestilence, and any success people enjoyed against disease was because of measures undertaken by health boards. The quarantine was invented in Ragusa (Dubrovnik) in 1377 and was subsequently employed from time to time by cities, with varying degrees of success, against potentially infected outsiders and especially against maritime shipping. The pest house, or lazaretto, provided a way of isolating the sick and the poor (regarded as purveyors of pathogens) during an epidemic while the wealthy followed the path of flight—"flee quickly, go far, and return slowly."

Despite their heavy burden of disease, as the eighteenth century got under way, some European populations were beginning to experience what the English physician Thomas McKeown (1976) terms "the modern rise of population." The reasons why this occurred—why an age-old cycle of population growth spurts, brutally reversed by soaring mortality, followed by demographic collapse, came to an end—has been and still is vigorously debated. Factors like the recession of plague and some positive steps in public health seem straightforward enough. Other factors put forth, such as a change in the nature of warfare, are a bit less convincing—especially in a century that began with Europe at war over the question of the Spanish succession and closed with France and England locked in a global struggle, with a series of almost countless struggles in between. One can grant that, up to a point, armies were more disciplined than in the previous century, that they were frequently more isolated from civilian populations (which better distanced the latter from typhus and other diseases carried by armies), and even that advances were made in military hygiene, and yet still wonder if what has been granted might represent any significant decline in mortality.

McKeown, who sorts through the various possibilities, argues that improved nutrition was the key to understanding the process of mortality decline—an argument that has summoned numerous detractors, most of whom concede that this might be part of the answer but hardly the whole story. Undeniably, nutrition did improve for many, in no small part because of crops from America. Potatoes, introduced to Europe in the sixteenth century, had caught on (also squash to a lesser extent) by the end of the seventeenth century in Ireland and England and would soon do the same on the Continent. They not only provided a rich source of calories for the peasants along with a year-round supply of vitamin C, but were also an important hedge against famine. Maize, as we saw, brought pellagra to southern and eastern Europe where the grain was consumed by humans. In northern Europe, however, it became an important crop for feeding livestock, permitting more animals to be carried through the winter and thus ensuring a greater availability of animal protein year round in the form of milk, cheese, and eggs, as well as meat.

Among other things, more protein in the diet, so crucial to combating pathogenic invasion, would have helped in significantly reducing infant and especially child mortality in an age that had previously seen between a third and a half or more of those born fail to reach their fifth birthday—often because of protein energy malnutrition (PEM). This comes about when malnutrition and pathogens work together, as they frequently do, in a process called synergy, whereby the pathogens enhance a protein-deprived (and hence malnourished) state, which, in turn, leaves the body even more defenseless against the pathogens. Thus the greater availability of protein would have altered one side of the synergy equation, while a general reduction of pathogens would have done the same for the other.

The protein intake of a population can be judged, to some extent, by the average height of that population, and although there is dispute over places and times at which populations began to grow taller in Europe, there is no argument that European populations of the eighteenth century would have towered above their predecessors of a couple of centuries earlier. The armor of the warriors of those chivalrous days was, as a rule, constructed for much smaller people, suggesting that nutrition (especially protein intake) had, indeed, improved as Europe passed through its century of Enlightenment.

The Enlightenment was an age of increasingly strong states, a factor that affected the other side of the synergy equation because strong states were frequently able to compel pathogen reduction, albeit often serendipitously. Strong states, for example, were better able to regulate maritime commerce, and such regulation, with its delays and red tape, often became a quarantining device in itself, even when quarantines were not officially imposed—although, of course, strong states were better able to accomplish these as well. They were also able to insist on cleaner cities, not because monarchs and their officials were ahead of their time in grasping the nature of pathogens and their vectors, but rather because clean cities without raw sewage in the streets alongside decaying bodies of dead animals were considerably more pleasing aesthetically. The consequences, however, would have been a substantial reduction in disease vectors—especially flies, with their dirty feet. Such measures, along with the attention of the state to other matters such as drainage, could only have had a positive impact on public health.

This was also the case with more efficient agricultural practices that released more and more individuals from the countryside to enter the rapidly growing cities, where ever greater portions of populations became immunized in the process of converting epidemic and pandemic diseases to childhood ailments. And then, at the end of the eighteenth century, with the advent of the Jenner vaccine to replace haphazard and often downright dangerous variolation techniques, medicine finally made a significant contribution to population growth that would ultimately lead to the eradication of smallpox (save for that which remains in laboratories) some two centuries later.

IMPORTED PATHOGENS: THE EIGHTEENTH AND NINETEENTH CENTURIES

Two more new plagues struck Europe during the late eighteenth and early nineteenth centuries. One of these was yellow fever, a tropical killer to which Europeans had already proven themselves remarkably susceptible in Africa and the West Indies. The same susceptibility was apparent at home during periodic epidemics that had first begun striking Europe during the eighteenth century and continued to do so in the nineteenth. Yellow fever reached the Continent circuitously, moving first from Africa (via the slave trade) to the New World, whereupon Europeans carried it back to the Old. During the nineteenth century, however, after the legal slave trade had been abolished, the focus of the now contraband slave trade was narrowed to just Brazil and Cuba, and the mother countries of the Iberian Peninsula became especially vulnerable to yellow fever. The coastal cities of Oporto, Lisbon, and Barcelona bore the brunt of its assaults, although the disease did venture inland, even reaching Madrid in 1878. England, France, and Italy also saw yellow fever outbreaks on occasion as the disease radiated outward from Iberia.

A few yellow fever epidemics, however, were insignificant when compared with Asiatic cholera, which was by far the biggest epidemic news of the nineteenth century. Just as yellow fever was an African plague with which Europeans had no prior experience, cholera was an Indian disease that had been confined to the Indian subcontinent, where it had festered for some two thousand years or more. The Portuguese in India had described it as early as 1503, but a number of conditions had to be met for Europeans to confront epidemic cholera—a usually waterborne disease—on their own soil. Among these were transportation improvements in the form of railroads and steamships that could whisk cholera pathogens from city to city and port to port after another requirement had been met: an increased movement of people who could carry the disease away from its cradle on the Ganges. Still another condition had already been satisfied. The ever increasing crush of people in Europe's cities meant a huge demand for water from nearby lakes, rivers, and reservoirs, and in an age before sanitation procedures, such demand was generally met with water fouled by those swelling populations—an ideal situation for pathogens that traveled the oral-fecal route and were easily transmitted in water.

In 1817–1818 British troop movements in India widened the range of cholera within India, and in the 1820s the disease was extended beyond that subcontinent and into Russia, where it reportedly killed over two million individuals. This time cholera spared the rest of Europe, but in 1830–1831 it again reached Russia and, instead of pausing, marched across most of Europe by 1832. In Paris, gravediggers threw aside their shovels and fled, letting bodies pile up in the streets; in England, frantic mobs assaulted authorities attempting to enforce sanitation regulations and destroyed hospitals, even attacking physicians they suspected of somehow engineering the epidemic to ensure a better supply of bodies for dissection. From Europe cholera hurdled the Atlantic to reach the Americas even before it invaded the Iberian Peninsula in 1833 and Italy in 1835.

Cholera reached Europe again in 1848, 1852, 1854 (the disease was sufficiently widespread to make this the worst of the cholera years), and yet again in 1866. During the fifth pandemic (1881–1896) cholera at first only touched the Mediterranean shores of Europe, but it later became widespread in Russia and Germany. During the twentieth century, however, only eastern and southern Europe experienced the disease, and these outbreaks were sporadic.

In terms of overall mortality, cholera was not so great a killer as the bubonic plague that preceded it or the massive influenza epidemic that followed it. But it did spur important developments in public health, especially in the area of sanitation, and with the arrival of germ theory at the end of the nineteenth century, the causative organisms of many diseases, including cholera, became known.

PLAGUES OF THE MODERN ERA: THE NINETEENTH AND TWENTIETH CENTURIES

In the case of tuberculosis, however, knowing the pathogen that caused it did little to slow the course of this illness, which was already in decline. TB had become epidemic in Europe in the seventeenth century, beginning to peak at about midcentury and continuing at a high level of activity for the next quarter century or so. Then it receded until the following century, when it again surged around 1750 to become the major cause of death in most European cities for the next hundred years. About 1850, however, the disease began a decline that (save for a surge during World War I) continued until chemotherapy was introduced after World War II, finally giving medicine its "magic bullet" against this plague that had already been so mysteriously tamed.

In the eighteenth century, according to Hirsch, scarcely a year elapsed without typhus epidemics in one part or another of the Continent. It marched with troops, who scattered the disease about in the wars of the Spanish, Polish, and Austrian successions during the first half of the century, and in the Seven Years' War and the French Revolution during the second half. It was in 1812 at the battle of Ostrowo that typhus once again became decisive in warfare by joining the Russians and the weather in decimating Napoleon's forces. Of the close to 500,000 soldiers that marched on Moscow, only 6,000 made it home again.

Following this epidemic, typhus seems to have deserted the west and settled into the eastern portion of the Continent for good. The Franco-Prussian War of 1870–1871, for example, spawned no typhus epidemics, but the disease was omnipresent in the eastern European revolutions of 1848 and the Crimean War of 1854–1856. Similarly, during World War I there was no typhus on the western front, but it was absolutely rampant in the east among soldiers and civilians alike. During the first six months of the war, Serbia alone experienced some 150,000 typhus deaths—a horrendous toll, but nothing like the two and a half million typhus deaths estimated to have occurred during Russia's retreat of 1916, the revolutions of 1917, and the subsequent onset of civil war.

It was at this juncture that influenza also began to play a considerably larger role in world affairs. Barely active in the seventeenth century, the disease swept Europe with three pandemics in the eighteenth century (1729–1730, 1732–1733, and 1781–1782), along with several epidemics. In the nineteenth century, there were at least three more pandemics in Europe—those of 1830–1831, 1833, and 1889–1890—with the latter killing at least a quarter of a million people. This pandemic was diffused swiftly by the ongoing transportation revolution, providing something of a preview of what was to come; but none of this was preparation enough for the wave of influenza that began to roll in the late winter and spring of 1918.

The 1918 influenza seems to have arisen first in the United States but soon swept over Europe and its battlefields, and then reached out to almost all corners of the globe. The morbidity it produced was staggering, as hundreds of millions were sent to their sickbeds, but it was an ability to kill young adults as well as its usual victims—the very young and the old—that made this disease so deadly for so many. Global mortality has been estimated at over 30 million, of which Europe's share was placed at a little more than 2 million. Then, just two years later, another wave of the disease washed across the globe, after which it somehow dissipated.

The next apparent epidemic threat to a world badly shaken by influenza was poliomyelitis. It is very difficult to spy polio in the distant past because its major symptoms—fever and paralysis—are hardly distinctive. Many individual cases were described in the eighteenth century that could have been polio, and one is mentioned in England in 1835. However, the first clearly recognizable victims of epidemic polio are said to have hosted the disease in Norway in 1868. But cases that were regularly reported throughout the nineteenth century in Scandinavia as well as in Italy, France, Germany, and the United States are now understood to have been polio. At the turn of the century polio reached epidemic proportions in Scandinavia and continued to surge in these proportions well into the twentieth century. England, too, began to experience polio cases and by 1950 was second only to the United States in case incidence.

At this point, however, medicine began to assume its well-known role in the matter with first the Salk and then the Sabin vaccines; once these became available, in 1955 and 1960, respectively, they were widely administered throughout the United States, Europe, and much of the rest of the world, and fears of a global epidemic such as the influenza of 1918 quickly subsided. Humankind seemed to be entering a new era in which epidemic disease was no longer to be an important health factor. Antibiotics were controlling venereal diseases, tuberculosis appeared on the verge of extinction along with smallpox and most other killers of the past, and death rates from all causes had plummeted throughout the century, even though those subsumed under the rubrics of "diseases of the circulatory systems" and "malignant neoplasms" had more than doubled. The chronic diseases were seen to have replaced epidemic diseases as the real enemy, and medicine began training its guns on them, especially lung cancer, breast cancer, and heart related diseases, which, although not contagious, appeared to be assuming epidemic-like proportions.

Part of this development was explicable in terms of medicine's success against contagious illnesses: people were living longer, and many more than ever before were reaching ages when such illnesses were most likely to develop. In no small part longer lifespans were attributable to preventive medicine, which had been remarkably successful in fostering good general health, especially among infants and children. But in addition to lifespan, lifestyle was also implicated, and the concept of risk factors was introduced following epidemiological studies that established a causal relationship between the inhalation of tobacco smoke and both lung cancer and heart disease. A positive relationship was also found between high blood cholesterol, triglyceride levels, and coronary events (with high blood pressure and diabetes also risk factors), and the high fat content of Western diets was linked not only to elevated rates of heart disease but to some cancers as well—especially breast cancer.

Lifestyles, however, change slowly. Many people keep an eye on their diets, but many do not, especially those who find frequent comfort in traditional, often fat-laden, regional cuisines. And tobacco smoke has continued to spiral upward into European air. Something of an anomaly, however, has been discovered in the diet of people in Mediterranean countries, which is based on olive oil and wine and little in the way of animal fat; consumers of this diet enjoy relatively low levels of the chronic diseases despite cigarette smoking—suggesting that medicine, having identified risk factors, may still have much to learn about their modification.

Medicine also learned abruptly that it was not done with epidemic disease, for in 1977, at just the time when that profession was congratulating itself for apparently snuffing out smallpox forever, another global epidemic was in the making. The acquired immune deficiency syndrome (AIDS) began to surface during the late 1970s, as physicians in the United States reported a number of unusual disease conditions among otherwise healthy homosexual men. By 1981 the illness had been formally described, and by 1983 research in laboratories in the United States and France had identified its cause as a previously unknown human retrovirus, HIV-1. It was determined that the virus passes from person to person through bodily fluids. The disease had seemed at first to be an exclusively American problem that was centered in the country's gay communities and among injection drug users who shared needles, but it quickly became apparent that Caribbean populations and Africans south of the Sahara were also afflicted with this horrifying ailment, which causes the immune system to collapse. Then in 1985 a related virus, HIV-2, which passes through heterosexual activity, was discovered to be widespread in Africa.

With many of its citizens having contacts in the United States, the Caribbean, and Africa, Europe had no chance of escaping AIDS; in addition, many of its hemophiliacs were infected with blood from America. By the early 1990s the disease had spread throughout the world, and in 1996 the number of cases was estimated to exceed 22 million. In 1997 the European Centre for the Epidemiological Monitoring of AIDS pointed out that the fifteen countries of the European Union had 93 percent of Europe's AIDS cases and predicted a rapid case increase in the rest of Europe, with much of this the result of heterosexual contact.

Although about 90 percent of the more than 22 million cases in the world are in developing countries, some 2 million are not—and these patients have found themselves subjected to the same kind of cruel stigmata that plague and syphilis victims experienced centuries before. Indeed this latest plague, which at one time was regarded as the Black Death of the twentieth century, came not only at a time of medical complacency but also at a point when any social or political experience in confronting such a widespread public health crisis had long since been forgotten. In the West medical science at the turn of the century began at last to have some success in grappling with the disease—at least in increasing survival time—and the din of stigmatism faded somewhat. But the epidemic is far from over, and sequels such as a sharp increase in the incidence of tuberculosis also remain to be dealt with.

AIDS administered a number of brutal lessons, and one stands out starkly. The disease showed how, in an age when one can travel to almost any place on the globe in a matter of hours, the West is now vulnerable to diseases that break out anywhere in the world. Globalization of pathogens seems as inevitable as the globalization of food and economies, and as a consequence, it appears doubtful that we can hope to experience any reprieve from epidemics of the kind that ranged from the influenza of 1918 to AIDS.

See also other articles in this section.

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