Biology of Plagues: Evidence from Historical Populations (review)

Susan Scott and Christopher J. Duncan. Biology of Plagues: Evidence from Historical Populations. Cambridge: Cambridge University Press, 2001. xiv + 420 pp. Ill. $100.00 (0-521-80150-8).

It has long been doubted whether the plagues that attacked Europe between 1348 and the end of the seventeenth century can be attributed to bubonic plague and its infective agent, Yersinia pestis. The disease spread too quickly over vast areas for it to have been caused by a rodent-based infection, spread from rats to men by fleas. There are no contemporary descriptions of mortality among rodents, and the climatic conditions necessary for high flea-densities did not obtain over most of Europe. Studies of bubonic plague in India in the modern period provide more contrasts than comparisons with the historic experience in Europe.

Susan Scott and Christopher Duncan add powerful support to the skeptical case. They summarize previous findings, and contribute material and arguments of their own. In particular—and this is their major contribution—they have painstakingly studied the temporal and familial incidence of mortality in particular epidemic outbreaks. One of them is the plague in Penrith, England, in 1597-98, on which they are acknowledged experts. Others are the famous epidemic in Eyam in 1666, and some of the London outbreaks of the seventeenth century. From this assorted evidence they reach the important conclusion that there was an average period of thirty-seven days between the point of individual infection and death—long enough to explain much of the movement of plague over space, while allowing concentrations of high mortality in crowded cities, given direct transmission from person to person.

The authors go on from this to much broader conclusions. Neither bubonic nor pneumonic plague will explain the historical phenomena. A single disease, which they term "haemorrhagic plague," ravaged Europe from 1348 to about 1670, and it was "an infectious disease (probably viral) spread person-to-person" (p. 394), perhaps caused by a filovirus (p. 389). Only one piece of evidence gives them pause: the DNA extracts from dental pulp in skeletal material, which have recently confirmed the presence of Yersinia pestis in 1722 and earlier "plague" years in mass graves in Marseilles and French Provence. But Scott and Duncan deal with this difficulty by arguing that true bubonic plague may well have caused epidemic mortalities on the Mediterranean coast of Europe (including in Italy) while haemorrhagic plague was dominant further north.

Their argument at this point is less than wholly convincing. Although there were clearly climatic differences between southern and northern Europe, the differences between plagues in Marseilles and Italian cities and those in London and Paris are not as stark as the authors would have us believe, and those in the south were scarcely closer in character to plague epidemics in India than were those in the north. There are sometimes weaknesses also in the authors' use of historical evidence. It is surprising to find J.-N. Biraben's graphs of references to outbreaks of plague being taken to demonstrate a shift toward greater frequency of epidemics after ca. 1500, for example, when the nature of the historical record—and hence the likely survival of contemporary references—notably changes around that date.

Nevertheless, there is important material here which every historian of plague must ponder seriously. Scott and Duncan tell us more than previous writers about the local epidemiology of plague outbreaks, and they have much of interest to say about their character in different countries and about their ongoing demographic consequences. Stimulating as it is, however, their case for a viral haemorrhagic fever as against Yersinia pestis must necessarily remain unproven. What we need now are more analyses of skeletal material and surviving DNA. If evidence were to be found of Yersinia pestis in mid-fourteenth-century London, or in the London of 1665, that would really set the archaeological cat among the epidemiological and historical pigeons, and make us all...