Ancient 'Black Death' plague strain 'could re-emerge in future'

A team of scientists has discovered that two of the world's most devastating pandemics - the plague of Justinian and the Black Death, each responsible for killing as many as half the people in Europe - were caused by distinct strains of the same pathogen.

The strain that helped bring an end to the Roman Empire faded out about 1,500 years ago on its own. But the other, which flourished 800 years later, led to worldwide re-emergence in the late 1800s and is still with us today, killing thousands each year.

The findings suggest a new strain of bubonic plague could emerge again in humans in the future.

Dave Wagner, an associate professor in the Center for Microbial Genetics and Genomics at Northern Arizona University, said the Justinian strain, which earlier research traced to having its origins in Asia, lies "smack between" two groups that are still found in China.

He said that it's pretty interesting that it moved all the way to Europe and went extinct and could still be out there somewhere between Europe and China but we haven't seen it yet.

The plague of Justinian struck in the sixth century and is estimated to have killed between 30 and 50 million people- virtually half the world's population as it spread across Asia, North Africa, Arabia and Europe. The Black Death struck about 800 years later with similar force, killing 50 million Europeans between 1347 and 1351.

The results are currently published in the online edition of The Lancet Infectious Diseases.