The Emergence and Development
of the Notion of Contagion

F. GONZALEZ-CRUSSI, MD

aSpring 2000

Adapted from a paper read at the Annual Meeting of the Society for the History of Pathology, a companion society of the International Academy of Pathology, at Nice, France, 1998.

Epidemic diseases  have always struck terror in the afflicted populations. And with good reason. It is well known that Europe in the Middle Ages was devastated by epidemics of plague. Starting with the pandemic of 1348–51, successive waves of this disease brought enormous damage to the population of entire countries. Of those affected with plague, 80% died in less than a week; and in the towns, 20 to 50% of the population fell ill. These sobering facts prompted much speculation and medical efforts to understand the cause of epidemics; but before the advent of modern microbiology, no real understanding was possible.

TRANSPLANTED DISEASES BECOME ESPECIALLY DEADLY

One important observation was that epidemics took on a new, much increased aggressiveness when transplanted to a new location. Such was the case with smallpox when it came to the New World in 1518, brought by the Spanish conquistadors, and first spread in the islands of Cuba and Hispaniola. No sooner had the Spanish landed in the peninsula of Yucatan, in 1519, than the epidemic was raging among the natives. The king of the Maya Indians and his eldest son died that same winter, as did many of the Maya potentates.

The rapid spread of the disease led the Mayas to believe that the evil gods of illness, the three children Ekpetz, Uzannakak, and Sojakak, took the disease from house to house at night. The Maya communities were almost annihilated. The destruction was much worse than the Spaniards could have thought of inflicting by military aggression. A sacred book of the Mayas, known as the Chilam Balam, described the old days before the conquest with nostalgia: "Then there was no sickness; they had no aching bones; they had then no high fever; they had then no small pox; no stomach pains; no consumption. At that time people stood erect. But then the teules arrived [a corruption of the Indian word teotl, demigod-god, or supernatural personage], and everything fell apart. They brought fear, and they came to wither the flowers...."

The Aztecs were next. They were by no means healthy. They suffered from gout, cancer, congenital deformities, and assorted parasitosis. They had all sorts of skin diseases, which they believed sent by the god Macuilxochitl (meaning "five flower") in punishment for transgressions against the mandate of sexual abstinence during high and holy religious days. But they were new to the infectious diseases brought by the invaders. Consequently, the mortality was appalling, and the manifestations of the disease uncommonly virulent. Conjunctival hemorrhages, hematuria, excruciating bone pain, not regularly present in the European patient, were often seen in the non-immune Amerindian population. Prostration was extreme, and death followed swiftly.

The Mexicans, like other Amerindians, were most grievously decimated. Their traditional medicine was woefully useless. The Indian custom against skin rashes was to bathe. Against smallpox, this remedy did not work. They applied bitumen, which they rubbed against the affected part; and they traveled long distances to their most venerated temples for this ritual cure. It did not work, either. Then they used tobacco, or consumed hallucinogens, and repeated incantatory, magical formulas. They even poured pulque, the fermented drink from the agave plant that is still widely consumed in Mexico, directly onto the skin lesions. Nothing seemed to work.

As with smallpox, so with other infectious diseases. Mumps, measles, tuberculosis—the diseases of civilization—struck with equally deadly force and brought forth manifestations of such severity as were rarely seen in Europe. Nineteen major epidemics are said to have occurred in New Spain in the century that followed the conquest. In the Valley of Mexico, there may have been approximately 1.2 million inhabitants before the arrival of Europeans. By the year 1650, after one century of Spanish colonization, and when the Indian population had begun to stabilize, their number was down to only 70,000. This was the combined result of war, enslavement, malnutrition, and other factors. But the major cause was epidemic infectious diseases brought by the Spaniards. I suppose today we might say they waged "bacteriological warfare." To judge by the results, the destruction was bigger than any ever inflicted upon any ethnic group; and this includes the genocidal holocaust wrought against European populations during the Second World War.

IMMUNITY SEEN AS ‘GOD’S FAVOR’

It could not have escaped the notice of both warring camps that the Indians succumbed when the Spaniards survived or were spared, a fact that greatly facilitated the conquest. Beset by strange illnesses, debilitated by sores and fevers, depressed upon confirming the impotence of their best medicines and the growing panic of the population, the Indians became utterly demoralized. They ended up believing that the Spaniards were, if not on a par with the gods, certainly endowed with supra-human vigor; and beings of such resilience were bound to emerge victorious. Accompanying the conquistadors, came many friars; and among these, learned theologians, and some casuists famous for their subtle reasoning. One of them was quick to point out: "God kills them and preserves us." In other words, Spanish survival in the face of Indian mortality bespoke partiality of Divine Providence for the men who fought to eradicate heathenism, and to implant the one and only true faith, the Roman and Apostolic Catholic religion. Today, most of us believe that Castilians or Extremadurans, being Europeans, had lived through one or more epidemic waves, including perhaps out-breaks of plague, by the time they reached adulthood. Their immunity was thus strengthened through previous exposure. But, at the time, Europeans drew solace from belief in divinely ordained protection, while the natives, in their misery, subscribed to a nonrational belief that recurs in history: that catastrophe was the punish-ment the people had merited from angry gods, by some misconduct.

SYPHILIS, THOUGH, SHOWS LITTLE FAVORITISM

The Europeans, it seems, were not previously exposed to syphilis. The origin of this disease has been hotly debated for many years, but the majoritarian body of opinion holds that it originated in America. Accordingly, syphilis thrived vigorously, as infectious diseases are wont to thrive in a virgin soil. Millions of Europeans fell ill; the Treponema spared neither prince nor pauper. Nor is this just a metaphor: simple peasants, kings, and even popes, acquired the disease. Historians tell us that Henry VIII died of syphilis; that Cesar Borgia refused to give audience in order to hide disfiguring lesions of secondary syphilis on his face; and that pope Julius II declined to offer his bare feet to be washed and kissed by the faithful, as required by Catholic ceremony, because he wished to conceal the luetic dermatitis that covered them.

CURRENT UNDERSTANDING OF THE PLAGUE

To better grasp the origin of the modern concept of contagion in European thought, it is useful to briefly sketch our current scientific understanding of plague, the paradigmatic epidemic disease. Today, most educated persons know that plague is a disease caused by bacteria, Yersinia pestis, that habitually infect rats and other rodents, and is transmitted to man by fleas. In a typical example, a flea feeds on a rat’s blood, and subsequently bites a human being and so transmits the disease. Transmission, therefore, follows the path rat-to-flea-to-man. French researchers in North Africa established that the human flea, Pulex irritans, can be more dangerous than the rat’s flea, because much more numerous, in transmitting the disease to humans. Also, a human flea may transmit the disease by feeding on a human patient and subsequently biting a susceptible, healthy human being. In this case the pathway followed by the infection is man-to-flea-to-man. Lastly, when there is pulmonary involvement, droplets of mucus bearing bacteria can be expectorated into the air, and be directly inhaled by a susceptible host. In that case, the route of transmission is man-to-man. Knowledge of these basic facts enables any informed person to predict that conditions which foster the proliferation of rats and fleas close to humans favor the spread of plague; and, conversely, circumstances that hamper the concentration of rats, fleas, and their contact with humans will correspondingly minimize the risk of an epidemic of plague.

WHEN THE 'MIASMATIC PARADIGM' RULED

It is obvious, however, that all these considerations on viruses, animal hosts, insect vectors, and routes of transmission, presuppose awareness of modern, scientific concepts of infectious disease. In the pre-microbiology era none of this was known, and medical European thought was dominated by what an Italian historian, Carlo Cipolla, has called the "miasmatic paradigm." Contagion was thought to arise from exposure to unhealthy, "corrupted" air, although the precise nature of this noxious influence was left vague. Ambroise Paré wrote of "a certain poisonous and venenate malignitie, the force whereof exceeds the condition of common putrefaction." Likewise, Robert Boyle wrote that plague "is carried by a malignant disposition in the air; without which some plagues could never have been so catching, as they were," but did not clarify further.

Plague fighter. This protective garb was developed in the Middle Ages for doctors to wear when plague was rampant. The 'beak' contained pleasant-smelling substances to mitigate the evil odors inevitably encountered.

"Infected," or "pestilent" air, denoted miasmas or exhalations rising from a variety of sites: marshes, stagnant ponds, caves, volcanoes, and putrefying bodies. A bewildering number of circumstances could "infect" or "corrupt" the air—or rather the atoms of the air—for most authorities believed, as we do today, in atoms. The corpuscular philosophy, propounded in antiquity by Lucretius and the Epicureans, maintained the existence of atoms so small as to be invisible to the unaided eye. Declared Boghurst in 1665: "The seeds of the pestilence are so hidden and removed from sense, that we see them better in their effects than we can in themselves." Heat, humidity, an inauspicious conjunction of the stars, sudden wind currents, effluvia from animal skin, especially from furry animals: all were imagined potentially capable of conveying pestiferous atoms, and thus transmitting the plague.

In this scheme, the pathways followed by infection were dauntingly numerous: marshy water-to-man, animal-to-man, dead body-to-man, rotting wood-to-man, metal-to-man, cave-to-man, and so on. The pathways were simple and direct, less convoluted than those which modern science teaches, but frightening by their overwhelming profusion. Disease could come from anywhere. It could issue literally "out of the blue sky," since it resided in spoilt atoms, the "poisoned corpuscles" of the air. Is it not true that odors suffuse the substance of garments? Well, so can pestiferous corpuscles. Perfumed gloves kept in a drawer for twenty years retained their aroma. Likewise, the straw from a mat on which a patient with plague had slept, kept its contagiousness years after the patient had died. Is it not true that poisonous metals exist underground, as evinced by the insalubriousness of mines and the short lives of miners? Why, this explains that plagues are common after earthquakes, when mortiferous exhalations are released through cracks and fissures of the earth’s surface. Epidemic contagion was thus conceived as a fiendish, demoniac threat; it was invisible, imperceptible, and lurked almost anywhere, ready to spring on its victims without warning.

LOGICALLY CONSISTENT, YET SO WRONG

Think of this: A totally erroneous hypothesis dominated European medical thinking for centuries, between the end of classical antiquity and the beginning of the modern era. Why this error lasted so long is an intriguing paradox for historians. One explanation advanced is that the "miasmatic theory" had a perfect logical consistency, and was beautifully adapted to accommodate every new observation, without losing credibility. For instance, it was correctly pointed out that plague was more likely to break out during the summer months. This true fact was correlated with a greater number and offensiveness of pernicious miasmas. No one thought of linking the factual observation with a greater number of rats and fleas. After all, everyone was used to rats and fleas in those times. As late as the beginning of the present century, if you were traveling in certain parts of Italy or Southern Europe, and were going to stay overnight at an inn, you probably would ask the innkeeper to bring to your room four large basins filled with water. Then you would ask someone to help you raise the bed, and immerse each of the legs of the bed into the respective water basin. This was a standard precaution recommended to all travelers, including refined aristocrats on their continental Grand Tour, to prevent blood-sucking vermin from crawling from the floor to the bed.

FRESH AIR WAS NOT ALWAYS FRESH

And it was a fact that bad odors, repulsive and presumably insalubrious emanations, were more prevalent during the summer months. For not even the most romantic and idealized view of the past should make us forget that, before the invention of the automobile, when horses were the main means of transportation, there were great piles of manure lying on the street; and before the invention of modern sewage, human excrement and urine were often thrown from windows into street and back alleys; and before the creation of modern sanitation, piles of refuse and filth were a familiar spectacle in many public places. The terrible stench rising from these sources must have been hard to bear. Consequently, the enhanced likelihood of plague in the summer months actually reinforced the theory that plague was due to poisonous emanations.

By the same token, the observation that those who handled bales of wool, hemp, or furs were at greater risk than those who handled smooth materials, such as glass or marble, was factually correct. But it was attributed to the greater ability of wools, furs and hairy objects to retain corrupt atoms of the air. It never occurred to the best minds that the real reason was that wools and shaggy carpets were likelier to harbor fleas, and that these, in actuality, were the transmitters of the plague. We have all seen illustrations of the seventeenth century costume donned by French physicians in times of epidemic plague. It consisted of a robe made of a waxed fabric (toile cirée), and a mask for the face with a beak-like part jutting out, that made the wearer resemble a raven. The beak was supposed to contain some salutary herbs capable of filtering the harmful emanations. And the alleged benefit of the waxed robe was that the insalubrious atoms in those miasmas would glide over its smooth surface without sticking to it. If this strange attire ever worked—and it may have, under certain circumstances—its protective power would have been related to the difficulties that fleas encountered in colonizing a smooth, waxed fabric. But the explanation also fitted the miasmatic theory, that the pernicious atoms could not stick to a smooth surface. In fact, the greater irony is, that the observation appeared to fit better into the miasmatic paradigm, than into the modern microbiologic scheme. This is what Cipolla has called the "perverse" quality of the miasmatic hypothesis: that every correct observation could be accommodated into it, and none of thousands of accurate observations ever cast any doubt upon the hypothesis, but actually seemed to reinforce it.

SOMEDAY OUR TREATMENTS WILL APPEAR BARBARIC, TOO

We should guard ourselves against feeling contempt for these old errors. The achievements of physicians of past eras were no less important than ours. And our ignorance in many respects is no lesser than theirs. It is a safe bet that, one day, some of today’s state-of-the-art treatments for cancer will appear incredibly barbaric to physicians of the future. And some of our most cherished hypothesis will seem outlandish, misguided, perhaps even laughable, to future scientists. Girolamo Fracastoro, a pioneer of epidemiology in the Renaissance, advanced coherent and lucid arguments to explain the routes of transmission of infectious diseases. It seems funny to us that his description of syphilis should have been in the form of a poem, that most unscientific of languages. But his insights of contagion by direct contact, by carriers or fomites, and by airborne dissemination, were perfectly accurate. When epidemic disease was universally regarded as celestial punishment for human wickedness, and this belief supported by references to Holy Scripture, to have recognized that there are specific patterns of transmission, was a monumental achievement. And Fracastoro was only one in a long line of outstanding researchers in quest of a true understanding of contagion. Of this line, the "crowning glory," as some have called him, is of course Louis Pasteur. But Pasteur himself was extending the ideas of others who rejected the corpuscular theory and foresaw, without being able to prove it, that infectious disease was caused by living germs.

CONTAGION—PLUS HUMAN FOLLY—SHOULD MAKE US WORRY

Contagion, some scientists say, will become the chief problem for mankind. Experts believe this will be a consequence of global warming. An article in the Lancet (published in 1992) attributed the 1990 cholera epidemic in Latin America to warming of the tropical Pacific by El Niño. In 1996, the JAMA warned that the ill effects of global warming will run the gamut from malaria to arbovirus, and from cholera to toxic algae. In 1995, an article in Science was entitled "As The Mercury Soars, So May Health Hazards." However, Science published a disclaimer editorial on November 1997. It was hardly reassuring. Here, a distinguished virologist was quoted as saying that global warming was not the problem. The key factors are different, such as drug resistance of parasites, and pesticide resistance of vectors. But this is not all. There is also breakdown of public health measures, as during wars, terrorism, or plain social irresponsibility. Recall the environmental degradation and poor state of health brought about by such disasters as Chernobyl, and it should not be surprising to see new epidemic outbreaks. Remember that homelessness, crowding, and poor nutrition exist in many societies, and the transmission of infectious disease will not seem at all unusual. In the United States, economic changes have eroded the health care infrastructure: with less public spending for anti-tuberculosis programs, it should not be surprising to see a reemergence of tuberculosis in urban centers.

In other words, it is not infectious disease per se that is the supreme worry, but infectious diseases brought about and compounded by human folly. Not cholera, small pox, or equine encephalitis, but these diseases in their corresponding social, economic, and political contexts. Infectious diseases by themselves are only disorders caused by microorganisms. As such, they are an important but relatively simple matter. But contagion as an offshoot of industrialization, magnified by mistrust and prejudice, fortified by ignorance, complicated by violence and combined with human callousness: that is a more serious condition, la maladie du siècle, the real malady of this century.

Seen from this perspective, contagion itself seems relatively minor. Nonetheless, we should do something about it. Let me end by quoting some remedies advocated by Umberto Eco in a darkly humorous essay entitled "How to Avoid Contagious Diseases":

"Take care not to be kidnapped by terrorists: the kidnappers as a rule use the same hood for many terrorists [this practice, Eco condemns as unhygienic]. . . Political prisoners must take great care to elude the backhand slap of the police, striking their mouths after similarly touching the gums of other persons held for questioning. . . Further risk of infection is posed by the dying who kiss crucifixes, and by those sentenced to death, as the blade of the guillotine is seldom properly disinfected after each use. . . Avoid areas subject to bombardment by nuclear warheads: faced with the sight of a mushroom cloud, the spectator has an instinctive tendency to put his (unwashed) hands to his mouth, as he murmurs ‘My God!’"

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