Detecting Plague: Palaeodemographic Characterisation of a Catastrophic Death Assemblage

Article excerpt

Introduction

The palaeodemographic signatures of epidemics are of perennial interest to biological anthropologists. It has been demonstrated that patterns of human mortality generally demonstrate a high degree of uniformity across populations (Paine 2000:181). This is referred to as attritional mortality and is characterised by a high number of infant deaths, low numbers of adolescent deaths and a gradual increase in mortality throughout adulthood. By contrast, an episode of catastrophic mortality refers to a short-term mortality crisis in which a high risk of death applies to all age categories. The identification of catastrophic as opposed to attritional mortality profiles in archaeological samples of human skeletons clearly has important social and palaeopathological implications (Paine 2000). A catastrophic mortality profile should mimic the age structure of the living population because all individuals have an approximately equal probability of dying irrespective of age or sex (Keckler 1997). Catastrophic mortality is almost by definition unusual, as a population subjected to frequent episodes of catastrophic mortality would rapidly become extinct.

The bubonic plague is an example of a disease that can cause catastrophic mortality because it is highly infectious and has a high case-fatality rate when untreated. Currently the demographic effects of pre-modern catastrophic events, such as the 'Black Death' plague that affected England in AD 1348-1350, are poorly understood. While the bubonic plague is strongly implicated as the cause of the Black Death, the event occurred prior to the detailed recording of mortality, and it is not known whether this plague episode resulted in a characteristic demographic signature that can be detected in samples of skeletal remains. The aim of our study was to examine the demographic structure of a sample of human skeletal remains that represent some of the victims of the 1348 plague, to test whether the skeletal sample exhibited a catastrophic age structure.

The Black Death

The Black Death swept from China and across Europe during the fourteenth century, causing devastating mortality. The 'Great Mortality' or 'Great Pestilence' (as it was referred to then) reached England in AD 1348. This plague episode, like the Great Plague of 1664, is generally believed to have been bubonic and possibly pneumonic plague, caused by the bacterium Yersinia pestis. The DNA of this organism has been identified from the dental pulp cavity of individuals excavated from a contemporary plague pit in France (Drancourt et al. 1998; Raoult et al. 2000; but see Wood & DeWitte-Avina 2003 and Mackenzie 2003 for critiques of this evidence). In bubonic plague the bacterium has an incubation period of approximately 2 to 8 days. Onset is acute with high fever, prostration and a characteristic infective lesion at the lymph nodes known as a bubo. In the premodern era there were no effective antibiotic treatments and the disease may have had a mortality of greater than 50 per cent (Benedictow 1987). Bubonic plague is a complex disease because it is primarily a zoonotic infection transmitted from animals: humans are incidental victims.

Some authors have questioned the interpretation of the Black Death as an outbreak of bubonic plague on the grounds that Yersinia infection could not have caused such massive and rapid mortality (Twigg 1984; Karlsson 1996; Scott & Duncan 2001; Wood et al. 2003). 'Plague' was (and still is) a generic word used to describe almost any fatal outbreak of disease. Contemporary descriptions tend to be embroidered, impressionistic affairs that hinder accurate diagnosis. This, coupled with the shortage of accurate mortality statistics, raises a number of epidemiological questions (Ell 1984). What is known is that from its port of entry in Dorset, the plague spread rapidly through England and reached London by 1348, finally abating in 1350. Estimates of mortality vary widely and the most often quoted figure is that one third of the total population of Western Europe died between 1346 and 1350 (McNeil 1976). …