Current DNA research suggests that the descendants of plague survivors share certain genetic changes, described as super-genes, that may extend life expectancy by providing protective immunity and resistance to certain cancers and auto-immune diseases. The theory interests me because two of my Italian ancestors may possibly have died of plague, My 8x-great-grandfather Michele and his son Giovanni died on the same day at ages 85 and 54, respectively. Their deaths could be attributable to factors other than plague – an accident of some kind involving father and son (perhaps a hunting accident); or wounds sustained in battle (Italy's history is littered with countless wars of territorial conquest and retribution); but their deaths on 26 February 1729, suggest that they may have succumbed to a catastrophic illness - a localised plague epidemic.
The first recorded plague pandemic (an epidemic affecting countries around the world almost simultaneously) began in Constantinople in the 6th Century, killing one-third of the city's population and spreading, over the next three years, to southern France, the Rhine valley and Iberia (Spain), eventually causing the fall of the Roman Empire. The second pandemic in the 14th Century killed one-quarter of the population of Europe (including 60 per cent of people in the British Isles), while the 19th Century pandemic originated in China, spread to Hong Kong and then to Australia; there were 12 major outbreaks of plague in Australia from 1900 to 1925, with 1371 cases and 535 deaths, mostly occurring in Sydney (Curson P.H. Times of Crisis: Epidemics in Sydney 1788-1900. Sydney: Sydney University Press, 1985).
Pandemics cause social, cultural and economic upheaval but are relatively short-lived - because they kill almost everyone who becomes infected. In the years between the second and third plague pandemics, localised outbreaks occurred sporadically throughout Europe, the Middle East, and Africa owing to increases in population density (crowded living conditions = more people available to
succumb to the infection) but also to changes in agricultural practices, from small-crop farming and single-animal husbandry to concentrated production of single species crops and animals to produce domestic surpluses that could be traded for other staples. These developments led to further expansion of trade routes which, in turn, made the spread of disease more likely. In medieval Italy, trade routes expanded inland from the port cities of Venice, Florence and Genoa, connecting previously isolated hamlets with the urban populace. These changing social and economic conditions prevailed in Italy during the 1700s, when Michele and his son Giovanni lived in a small village about 70km northeast of Venice.
The causative agent of plague is the Yersinia bacillus endemic to certain rodent populations; flea-infested rats spread plague over long distances. But in medieval times disease (and especially plague) was viewed as God's judgement upon a wicked world, evidenced by the fulminating nature of plague that resulted in a mortality rate of nearly 100 per cent. There would have been nothing more frightening than the appearance of blackened swellings in armpits and groin, a raging fever quickly followed by gangrene of the extremities, delirium and death within 48 to 72 hours. Whole villages were wiped out. Early accounts of plague-ridden populations contain chilling descriptions of corpses stacked up in lane-ways because there were no grave diggers to bury them, no clergy to perform burial rites.
Fifty-something Giovanni was almost certainly the primary provider for an extended family that included his ageing father Michele. Giovanni would have dealt with merchants and may even have plied the trade route to Venice, increasing his exposure to both human and animal vectors of plague. Giovanni's comparative youth and presumably strong physical condition may have delayed the onset of infection but Michele, weakened by old age and possibly by pre-existing illness, would have succumbed more readily. Giovanni's sons, with under-developed or compromised immune systems, may also have succumbed (their death dates are unknown), but the fact that father and son died on the same day is, to my mind, more than coincidental, and the familial relationship is key to my belief that they died of plague because communal living conditions of the period in which they lived would have been ideal for the spread of fleas.
Plague had drastic and permanent effects on the social fabric of the entire world. Food production was severely disrupted because there were fewer hands to grow and harvest food. Famine usually followed a plague epidemic. The number of plague deaths reduced the number of available marriage partners at a time when producing children was essential in order to prevent extinction of an ancestral line (or an entire cultural or national grouping). Mating between survivors provided benefits – it reduced the pool of potential plague victims by strengthening the immune systems of the resulting offspring. The plague bacillus also benefited: successive plague outbreaks killed fewer and fewer people, ensuring the survival of the bacillus - it couldn't live without a host to infect and needed time to reinvigorate; this, along with scientific and medical advances, explains the episodic nature of contemporary plague epidemics (the most recent in the 1950s that killed more than 15 million, most of them in India; Butler T. Plague and Other Yersinia Infections. New York: Plenum Medical Books, 1983).
The widespread social and economic disruption that accompanied plague pandemics altered cultural distinctions between communities and between the nations of the ancient world (Rosen, W. Justinian's Flea: The first great plague and the end of the Roman Empire. New York: Viking Penguin, 2007). Accounts of the medieval plague pandemic, such as Boccaccio's Decameron (1348), contain vivid descriptions of 'the pestilence', as plague was then known. Contemporary studies of the consequences of plague have increased our understanding of the epidemiology of plague and led to improvements in public health policy and the development of pharmaceuticals to combat infectious disease epidemics.
For my family, the consequence of the 14th Century plague pandemic may be the legacy of a super-gene that confers survival benefits on those of us who carry it, courtesy of Michele and Giovanni.