Genetic profile of 6th century plague offers clues to how pandemics spread
Lessons in mutation and emergence of novel germs from sequencing of 6th century scourge
A single pathogen has been identified as responsible for the Plague of Justinian and Black Death, deadly pandemics eight centuries apart which each annihilated half the population of Europe, a new study revealed.
The results, published in medical journal The Lancet Infectious Diseases on Tuesday, showed that in each case, the pathogen causing bubonic plague had been transferred from rodents to humans. Researchers concluded that rodent species worldwide continue to be reservoirs for the pathogen, suggesting a risk that new plagues could emerge in the future.
The transmission of the pathogen can be likened to the current bird flu threat unfolding in China, Professor Edward Holmes from the University of Sydney told the South China Morning Post.
“There is an analogy with influenza in wild birds. Every now and again these wild bird strains can jump out into humans via poultry and cause human disease in the same way they jump from rats,” said Professor Holmes.
Two people have died in Hong Kong from the deadly H7N9 strain of bird flu and a third remains in hospital. The sale of live chickens has been banned in the city for three weeks and 20,000 live birds were on Tuesday culled in a local wholesale market.
The study confirmed a distinct version of the bacterium Yersinia pestis, previously confirmed as having caused the Black Death in the fourteenth century, was also the trigger of the Plague of Justinian some 800 years earlier. The pandemic is considered to be the first of the three human plagues and is believed to have first emerged in the sixth century in the ancient Byzantine capital Constantinople.
An international consortium of scientists examined DNA samples found on dental fragments from the corpses of German victims who are believed to have died between 541AD and 543AD. Estimates of the death toll from the Justinian plague range from between 25 to 100 million people worldwide.
Previous studies had confirmed the pathogen Yersinia pestis as the cause of the Black Death, which wiped out an estimated 75 to 200 million people between the 14th and 17th centuries, returning in the 19th and 20th centuries in the Third Pandemic to wipe out more than 10 million more victims in China and India.
The connection between the three of some of the most devastating outbreaks in human history is a significant finding, researchers say, as it allows them to better understand how the pathogen can change and adapt over time.
“By having the genome sequence of this ancient plague we can now look for mutations”, said Professor Holmes. “We have modern strains, Black Death strains and now Justinian strains. We can now look at these genomes very carefully.”
The study was carried out by scientists from the University of Sydney in Australia, Northern Arizona University in the United States and McMaster University in Canada.