Epidemic reflections

Biraben’s lists of plague epidemics register 8,068 outbreaks of plague in Europe in the nearly 300 years of the Second Plague Pandemic from the end of the Black Death to the time epidemic countermeasures began to have significant effect around the mid-1600s, namely the period 1356–1649. This indicates that on average 28 plague epidemics broke out in Europe each year, many of them simultaneously and independently at long distances. This feature of plague in Europe and adjacent regions in this period evidently must be some effect of the Black Death and reflect the presence of a source of persistence and continuity of plague.

In 2000 Keeling and Gilligan published an important article on ‘Metapopulation Dynamics of Bubonic Plague’ containing mathematical modelling of rat-and-rat-flea-based bubonic plague that demonstrated reasons for the persistence and recurrence of bubonic plague epidemics. By definition, a metapopulation consists of a group of spatially separated populations of the same species, in this case black rats, which interact at some social level or by some means of contact. This model is entirely based on the conventional theory that black rats and their consort of fleas (X. cheopis) constitute the epidemiological dynamics of the transmission and dissemination of bubonic plague, including in Europe: ‘bubonic plague is driven by the dynamics of the disease in the rat population’. It accords with all standard works on plague, and with the primary studies on plague. Within this conventional framework, Keeling and Gilligan developed an analytical explanatory model for the understanding of certain observed aspects of plague that reflected lasting effects of the Black Death because there was a dense presence of black rats where plague was circulating: