Copper engraving of Doctor Schnabel, a plague doctor in 17th-century Rome.
Yersinia pestis has played quite a role in history, wiping out hundreds of millions of people over time. In the first documented outbreak of the pathogen in Justinian in the 6th and 7th centuries, scholars believe as much as 40% of the population of Constantinople died. In fact, modern estimates suggest that half of Europe's population died as a result of this first plague pandemic before it disappeared in the 700s.
Then, in the 14th century, the second iteration of the pandemic began, what is now the famous Black Death—which caused the deaths of nearly 200 million people. The origin and exact spread of this pandemic is disputed to this day.
Last year, a team of researchers shed more light on the origins of the Black Death when they discovered a sudden surge of deaths in what is modern-day Kyrgyzstan. Analysis of ancient DNA suggested the spread of Y. pestis may not have been due to Mongol conquests in the 14th century, as previously speculated.
Now, scientists at the Francis Crick Institute have added another piece to the puzzle with their identification of three 4,000-year-old British cases of Y. pestis—the oldest evidence of the plague in Britain to date.
The plague has previously been identified in several individuals from Eurasia between 5,000 and 2,500 years before present, but hadn’t been recorded in Britain before this point in time. This strain of the plague—the LNBA lineage—was likely brought into Central and Western Europe around 4,800 before present by humans expanding into Eurasia. The study authors say their new research now suggests the pathogen also spread to Britain at that time.
For the study, published in Nature Communications, the team identified two cases of Y. pestis in human remains found in a mass burial in Charterhouse Warren in Somerset, and one in a ring cairn monument in Levens in Cumbria. The Charterhouse Warren site is rare as it doesn’t match other funeral sites from the time period—the individuals buried there appear to have died from trauma. Thus, the researchers speculate the mass burial wasn’t due to an outbreak of plague, but individuals may have been infected at the time they died due to other causes.
Pooja Swali, first author and Ph.D. student at Francis Crick, and team extracted ancient DNA from the teeth of 34 individuals across the two sites, screening for the presence of Y. pestis. DNA analysis identified three cases of Y. pestis in two children estimated to be aged between 10-12 years old when they died, and one woman aged between 35-45. Radiocarbon dating suggests it’s likely the three people lived at roughly the same time.
Using genome sequencing, Swali and team then showed that the identified strain of Y. pestis looks very similar to the strain identified in Eurasia at the same time. The individuals all lacked the yapC and ymt genes, which are seen in later strains of plague and known to play an important role in plague transmission via fleas. This information has previously suggested that this strain of the plague was not transmitted via fleas, unlike later plague strains. Additionally, the study authors say the wide geographic spread suggests that this strain of the plague may have been easily transmitted.
“We understand the huge impact of many historical plague outbreaks, such as the Black Death, on human societies and health, but ancient DNA can document infectious disease much further into the past,” said Pontus Skoglund, group leader of the Ancient Genomics Laboratory at Francis Crick. “Future research will do more to understand how our genomes responded to such diseases in the past, and the evolutionary arms race with the pathogens themselves, which can help us to understand the impact of diseases in the present or in the future.”