For four months after the Aztecs had driven Cortez and his men from their city, an epidemic of smallpox broke out among them, and the man who had organized the attack on Cortez was among those who died. Such an epidemic, striking an entirely inexperienced population, was dreadful in itself, and no one knew how to respond or what to do. Since the population lacked inherited or acquired resistances, something like a quarter to a third of them died from the initial onslaught.Moreover, it is worth considering the psychological implications of a disease that killed only Indians and left Spaniards unharmed. Such partiality could only be explained supernaturally, and there could be no doubt about which side of the struggle enjoyed divine favour.
Though important details remain unclear, the array of parasites that infest wild primate populations is known to be formidable. In addition to various mites, fleas, ticks, flies, and worms, wild apes and monkeys apparently play host to an impresssive roster of protozoa, fungi, and bacteria, not to mention more than 150 so-called arbo-viruses (i.e. arthropod-borne viruses, conveyed from one warm-blooded host to another by insects or other arthropods).
p. 41
It is in fact, mainly because sleeping sickness was and remains so devastating to human populations that the ungulate herds of African savana have survived to the present. Without modern prophylaxis, humans simply cannot live in regions where the tsetse fly abounds. Hence, until very recently, the vast herds of these regions have remained the prey of lions and of other well-adapted predators, but were spared more than casual contact with that far more destructive newcomer among the beasts of prey: humankind.
pp. 41-42
Looked at from the point of view of other organisms, humankind therefore resembles an acute epidemic disease, whose occasional lapses into less virulent forms of behavior have never yet sufficed to permit any really stable chronic relationship to establish itself.
Obviously human attempts to shorten the food chain within the toughest and most variegated of all natural ecosystems of the earth, the tropical rain forests and adjacent savanna regions of Africa, are still imperfectly successful, and continue to involve exceptionally high costs in the form of exposure to disease. That, more than anything else, is why Africa remained backwards in the development of civilization when compared to temperate lands (or tropical zones like those of the Americas), where prevailing ecosystems were less elaborated and correspondingly less inimical to simplification by human action.
pp. 74-75
Human efforts to reduce the number of rabbits in Australia took a new turn in 1950 when the virus of myxomatosis (a distant relative of human smallpox) was successfully transferred to the rabbit population of that continent. The initial impact was explosive: in a single season, an area as great as all of western Europe was infected. The death rate among rabbits that got the disease in the first year was 99.8 per cent. In the next year, however, the death rate went down to a mere 90 per cent; seven years later, mortality among infected rabbits was only 25 per cent. [...]Before 1950 myxomatosis was a well established disease among rabbits in Brazil. The virus provoked only mild symptoms among the wild-rabbit population of that country and exhibited a comparatively stable pattern of endemic incidence.
By the sixth century, when European medical writers finally recognized that measles and smallpox were distinct diseases, there is no doubt that both had become standard children afflictions, familiar in all parts of the continent, and of considerable demographic significance, inasmuch as many children died of one or the other, with or without additional complications. [...] The sequence of two devastating pestilences, the first coming between A.D. 165 and 180, and the second raging from A.D. 251 to 266, is exactly what one would expect—indeed what was required—if, one after the other, these two infectious diseases broke in upon the comparatively massive but previously unexposed population of the Mediterranean world.p. 134
The upshot, as is well known, was the breakdown of the imperial fabric in the western provinces and its precarious survival in the more populated east.p. 137
On the strength of a lengthy and exact description by Procopius, the so-called plague of Justinian(542-43) can confidently be identified as bubonic [...] The disease (or something very like it) had appeared previously in Egypt and Libya in the third century B.C., if a casual remark by a medical writer named Rufus of Ephesus (ca. 200 B.C.) is to be believed. Thereafter it disappeared until Justinian time.
[Some] time after 1252, when the Mongols first invaded Yunnan-Burma, they inadvertently transferred the plague bacillus to the rodent population of their own steppe homeland and thereby inaugurated the chronic pattern of infection which medical researchers discovered in Manchuria in our own time.
Even after the initial ravages of smallpox had passed, having killed something like one third of the total population, nothing approaching epidemiological stability prevailed. Measles followed hard upon the heels of smallpox, spreading through Mexico and Peru in 1530-31. Deaths were frequent, as is to be expected when such a disease encounters a virgin population dense enough to keep the chain of infection going.
[Although] in the eighteenth century the major triumphs of scientific medicine lay still in the future, it does not seem absurd to suggest that decreasing significance of epidemic disease, partly due to medical advances but mostly due to ecological adjustments of which men were entirely unaware, constituted an essential background for the popularization of “enlightened” philosophical and social views. A world where sudden and unexpected death remains a dreaded possibility in eveyone's life experience makes the idea that the universe is a great machine whose motions are regular, understandable and even predictable, seem grossly inadequate to account for observed reality.