Ruairidh Macleod - Lethal Outbreaks of Plague at Lake Baikal 5500 years ago
Plague is amongst the most devastating diseases in human history, however, early strains of Yersinia pestis, the causal agent of plague, lack virulence factors required for the bubonic form, and their severity remains unclear. Here, I describe strains of plague reported associated with early outbreaks among prehistoric hunter–gatherers in the Lake Baikal region in East Siberia, beginning from ∼5600–5400 years ago (cal. BP). These outbreaks occur across four hunter–gatherer cemeteries, with a 39% detection rate for plague across all sites. By reconstructing kinship pedigrees, we show that small familial groups are affected, consistent with human-to-human spread of the disease, and the first outbreak occurred within a single generation. Intriguingly, the infections appear to have resulted in acute mortality events, especially among children. Zoonotic transmission is separately indicated by a Brucella infection in one of the children. Interestingly, differences are noted in functional genomic variants in the prehistoric plague strains, including in the ypm superantigen known from Y. pseudotuberculosis today. The new strains diverge ancestrally to all known Y. pestis diversity and push back the Y. pestis divergence from Y. pseudotuberculosis by some 2000 years. These results show that plague outbreaks happen earlier than previously thought and were indeed lethal. The findings challenge the common notion that high population densities and lifestyle changes during the Neolithic transition were prerequisites for plague epidemics.
About the Speaker
Dr Ruairidh Macleod is presently a postdoctoral research associate with the COREX ERC project at University College London, working in the lab of Prof. Mark Thomas. He defended his PhD in December 2024, which was supervised by Profs. Eske Willerslev and Matthew Collins, at the University of Cambridge. He began working on ancient proteomics in his undergraduate, and then rapidly moved across to ancient genomics in his postgraduate research. The latter centred on large-scale studies of prehistoric hunter-gatherer communities in Northern Eurasia (particularly at Lake Baikal), alongside an ancient environmental DNA record of local ecosystem changes. His current work is in understanding the causes of change in Neolithic and Bronze Age Europe, particularly in the development of methods to integrate genomic and archaeological data types. From October 2025, Ruairidh will start a five-year independent research fellowship at All Souls College, University of Oxford.