Canadian researchers have genetically mapped the bacterium known as the Black Death, one of the deadliest pathogens in history that wiped out onethird of Europe's population in only four years during the Middle Ages.
Mapping Black Death marks the first time an ancient pathogen has been reconstructed in its entirety and will allow researchers to track changes in its evolution and virulence over time.
The study, published in the science journal Nature, sheds light on how epidemics develop and suggests a killer pandemic will not be caused by a deadly pathogen alone, but by a "perfect storm" of circumstances, said Hendrik Poinar, one of the lead researchers, from McMaster University in Hamilton, Ont.
He said the findings mark a new era of research into infectious diseases.
"For so many years, people focused on the pathogen," said Poinar, an evolutionary geneticist at McMaster's Michael G. DeGroote Institute for Infectious Disease Research. "It's one thing to talk about the pathogen, but it's another thing to talk about the disease."
The research team found there were few genetic changes between the ancient and modern version of the bacterium Yersinia pestis, which causes the bubonic plague today and whose relative is a harmless soil-based bacterium.
"The Black Death was the first plague pandemic in human history," said Johannes Krause, a professor at the University of Tuebingen, Germany, and another of the lead researchers on the international project. "Humans were [immunologically] naive and not adapted to this disease."
Another likely factor that worsened the Black Death's toll was social conditions: Poverty and malnutrition were rampant and the concept of hygiene was non-existent.
The onset of the so-called "Little Ice Age" could also have favoured the spread of the disease which, as with many pathogens, travels more quickly in cold climes.
No bug or virus has wiped out a greater proportion of humankind in a single epidemic than the Black Death.
The first outbreak of plague occurred in China more than 2,600 years ago before reaching Europe via Central Asia's "Silk Road" trade route.
It scythed through Europe from 1347 to 1351, killing about one in three of Europe's and nearly one in 12 of the world's population at the time.
"Plague was among the strongest sources of selection on the human population in the last few thousand years," Krause said. "People who were less susceptible due to mutations might have survived, and these [beneficial] mutations may have spread."
When put up against modern medicine, the Black Death is not very dangerous.
"Based on what we know from this [genetic] sequence, would modern antibiotics work on this? Yes," Poinar said.
The researchers studied DNA from the remains of 109 skeletons, now more than 650 years old, that were buried beneath the Royal Mint in London, England, just outside the walls of the Tower of London.
Poinar and his team took bone and teeth samples to gather whatever small bits of DNA they could find.
They then used what can be described as a magnetic fishing line to hook Yersinia pestis from the morass of viruses, bacteria and human genes.
That unique piece of technology - to fish for DNA- can now be used to study and reconstruct other ancient pathogens that turned into deadly killers, Poinar said.
"This technology will allow us to time travel and capture pathogens in the past, which was really [once] a pipe dream. We never thought this was possible," Poinar said.
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