STUDYING THE PLAGUE: RETRIEVING INFORMATION FROM THE PAST

Recently, due to COVID-19 pandemic, epidemic preparedness programs have received particular attention. Unfortunately, the importance of preparedness and rapid response to epidemic events reached politicians and the public only when it was too late to prevent or limit this infectious disease. This pandemic has rapidly exposed the enormous vulnerabilities of modern human societies; globalization, fast transport, climate change, high population density, and ecological transitions are all aspects of modern societies that can favour and influence the emergence of new and old human pathogens. Although it is currently impossible to predict the emergence of a new pathogen before it actually emerges, analysing past microorganisms and epidemics can allow us to learn from past successes and mistakes, so that present and future surveillance and monitoring programs can be improved. With these premises, this thesis project incorporates biological and historical investigations to examine which information related to microorganisms and epidemics from the past can be derived from remains of organic material and historical records. In the first part of the project, human teeth, recovered from an archaeological site dated to the period of the Milan plague of 1629-1631, were processed to investigate the presence of traces of Yersinia pestis, the causative agent of plague. Both DNA and proteins associated with the pathogen of interest have been searched. Preliminary results for these analyses were inconclusive, but the metagenomic analysis is still in progress and the results will be available in the next few months. During the second part of the project, historical and epidemiological investigations were carried out on textual sources associated with past plague epidemics. The first study (Manuscript n. 1) involved the development of a new informatic tool aimed at extracting useful information from a huge amount of textual data. This tool was applied to derive information regarding the 1720–1722 plague of Marseille and the 1629–1631 plague in northern Italy. The analysis of text related to these two epidemic episodes revealed that plague-related words were associated with the words “merchandise”, “movable”, “tatters”, “bed” and “clothes”, while no association was found with rats. These results support the hypothesis of a role of human ectoparasites during the second plague pandemic. Moreover, the results suggested a potential future application of this tool for the prediction of pathogen, responsible for a described disease, in ancient texts. The second study (Manuscript n.2) concerned the analysis of the progress of the plague epidemic that hit the city of Milan during the years 1629-1631. The registers of the deaths of the city of Milan for the year 1630 were digitized and subsequently used for the spatio-temporal analysis of the epidemic and historical events related to it; in particular, the effect that a religious mass gather had on the spread of the epidemic in the city was analysed. The last part of the thesis project was focused on the research and study of the bibliography concerning the paleomicrobiological studies performed on ancient human microbiota (Manuscript n.3).