I declare that the years since the beatific incarnation of the Son of God had reached the sum of one thousand three hundred and forty-eight, when in the illustrious city of Florence, the fairest of all the cities of Italy, a deadly pestilence appeared. It may have been disseminated by the influence of celestial bodies, or sent upon us mortals by God in His just wrath by way of retribution for our sins. The pestilence had its origin some years before in the East, where it destroyed an innumerable multitude of people and animals and propagated itself without rest, moving from place to place until calamitously, it had spread to the West.
In Florence, despite all that human wisdom and forethought could devise to avert it, the doleful effects of this pestilence began to be horribly apparent towards the beginning of the spring of that said year. Officials organised the cleansing of the city from the many impurities that dwelt there, all sick folk were refused entrance to the city, and the city organised the adoption of many precautions for the preservation of health; including humble supplications addressed to God, and often repeated both in public procession and otherwise, by the devout.
The symptoms were not the same as in the East, where an issue of blood from the nose was a manifest sign of inevitable death. Here in men and women alike it first showed itself through the emergence of a form of tumour in the groin or the armpits, some of which grew as large as an apple, others as an egg, which the common folk called “gavoccioli”. From the two parts of the body these deadly gavocciolo soon began to propagate and spread themselves in all directions; after which the form of the malady began to change, black spots began appearing, often on the arm or the thigh sometimes few and large, sometimes minuscule and numerous. And just as those gavocciolo were an inevitable sign of approaching death, so also were these spots on whomsoever they appeared. These maladies utterly defeated both the art of the physician and the virtues of physic; indeed, it was not obvious whether the disorder was of such a nature to defy treatment, or the physicians were at fault (for by now besides the qualified doctors there was now a multitude both of men and of women who practised medicine without having received the slightest tincture of medical science) and failing to understand the disease, failed to apply the proper remedies. Whichever it was, very few who succumbed to the pestilence ever recovered and almost all died within three days from the appearance of the first symptoms, and in most cases without any fever or other attendant malady.
The virulent nature of the pestilence was all the greater because the sick were apt to carry it through contact with the whole, just as fire devours things dry or greasy when they are brought close to it. Yet the evil went further, for not simply through speech or association with the sick was the malady passed to the healthy along with the consequent peril of death; but any that touched the clothes of the sick or anything else that had been touched or used by them, seemed to contract the disease as a result.
This story which I have to tell sounds so incredible that had I (and many like me) not seen it with my own eyes, I would not have credited it myself, even if it was told me by a reliable source, much less committed my story to writing.
I declare that the energy of the contagion of the said pestilence was such that it was not merely propagated from man to man but, more startling, it was frequently noted that if some other animal touched the belongings of one sickened or killed by the disease they not only sickened, but almost instantly died. Indeed I saw with my very own eyes the following event. The rags of a poor man who had died of the disease were strewn around in the open street, when two hogs passed that way, and after some time trifling with their snouts, they took the rags between their teeth and tossed them to and fro and then, almost immediately, they gave a few turns, and fell down dead, as if by poison, upon the rags which in that evil hour they had disturbed.

Boccaccio – Description of the Plague in Florence from Book1 of the Decameron