Woodcut of dying plague patients from 1532. Public domain, via Wikimedia Commons.
Researchers have uncovered the types of bacteria, viruses and parasites that plagued ancient humans across Europe and Asia as far back as 37,000 years ago.
An international team, including researchers from the University of Copenhagen, Denmark, Lund University, Sweden, Curtin University, Australia, has created an archaeogenetic-based map of human pathogens across both time and geography.
“Infectious diseases have had devastating effects on human populations throughout history, but important questions about their origins and past dynamics remain,” the authors write.
Modern medicine provides better prevention and treatment of many diseases, but this was not always the case.
At least a quarter of all children died before the age of 1 until 1850, with infectious diseases being attributed to more than half of these deaths.
The research, published in Nature, aims to construct a better understanding of how past epidemics emerged and what factors affected the spread of disease.
The team collected ancient microbial DNA from 1,313 ancient individuals from across western Eurasia, central and north Asia and southeast Asia to create the map.
These individuals lived during a 37,000-year period, spanning from the Upper Palaeolithic to recent history.
The team collected the DNA from bone and tooth samples.
“Expanding our analyses to the broader pathogen landscape allowed us to infer and contrast incidence patterns between different species and types of pathogens to a greater extent than previously possible,” say the authors.
Their research reveals that around 6,500 years ago, zoonotic pathogens emerged. Zoonotic pathogens are disease-causing infections that can be transmitted between animals
and humans.
Zoonotic pathogens peaked about 5,000 years ago, which coincides with the widespread domestication of livestock.
“Our current map shows clear evidence that lifestyle changes in the Holocene led to an epidemiological transition, resulting in a greater burden of zoonotic infectious diseases,” write the authors.
“This transition profoundly affected human health and history throughout the millennia and continues to do so today.”
In total, the study selected 136 bacteria and 1,356 viral genera to detect, with some of the most common bacteria being Streptococcus and Actinomyces.
However, these bacteria are commonly associated with the human oral microbiome, so considering the team used tooth samples, these results may be skewed.
“Our dataset provides a unique opportunity to investigate the origins and spatiotemporal distribution of human pathogens in Eurasia, expanding the known range of some ancient pathogenic species and identifying others not previously reported using paleogenomic data,” write the authors.
The findings challenge current historical understanding of early plague strains, with the team identifying cases of plague across the Late Neolithic (7000 BCE–4500 BCE) and Bronze Age (3300 BCE-1200 BCE).
The team found many instances across this period where individuals who were buried at a similar time were infected, suggesting a plague outbreak.
“These results indicate that the transmissibility and potential for local epidemic outbreaks for strains at those sites were probably higher than previously assumed,” the authors write.
While the team was able to detect previously undiscovered pathogens, others such as M. tuberculosis, the bacteria responsible for causing tuberculosis, were not identified.
The authors hypothesise this may be because the study heavily relied on DNA data from tooth and bone samples where M. tuberculosis is unlikely to be identified.
The team are hopeful, however, that more research into ancient human pathogens will help fill gaps in current knowledge.
“This map will develop as more ancient specimens are investigated, as will our abilities to match their distribution with genetic, archaeological and environmental data,” the authors write.