This Debilitating Disease Might Have Totally Unexpected Origins

A patient with tuberous leprosy in 1895. Wellcome Collection CC BY 4.0

Leprosy is one of the oldest recorded diseases in human history, but despite its fearsome reputation, scientists have never been able to pinpoint its origins. Thanks to dozens of leprosy-ridden skeletons and ancient genome analysis, we just got a lot closer to an answer – and it’s totally unexpected.

New research, published in the journal PLOS Pathogens, has traced 10 strains of the bacterium behind leprosy, Mycobacterium leprae, and discovered that its origins appear to be in Western Europe, not Asia like it was previously assumed. Most specifically, the oldest strain was discovered on a 1,600-year-old skeleton from Great Chesterford, a typical English village in Essex, UK.

Weirdly enough, this strain is also found in modern-day red squirrels, once more reaffirming the theory that squirrels were one of the main drivers of this disease in Europe throughout the Medieval Period. Along with this, the researchers discovered a surprising amount of diversity in the leprosy strains circulating Medieval Europe, indicating that the disease was well established across the continent

The bones of hands infected with leprosy. St Bartholomew's Hospital Archives & Museum/Wellcome Collection CC BY

The most common theories previously suggest that leprosy sprung out of China, East Africa, or the Middle East. With the discovery of the oldest known strain being found in the UK, it appears that leprosy could have originated in Europe.

“This latest research shows all the strains of the leprosy bacterium, were, in fact, present in Medieval Europe, which strongly suggests leprosy originated much closer to home, possibly in the far south-east of Europe, or western Asia,” study co-author Dr Helen Donoghue, from University College London, said in a statement.

“We now know from this study, that different communities spread leprosy to north-west Europe, compared to those peoples who passed different strains to central and south-east Europe, which may have spread along the Silk Road to China, and via the ancient trade routes to Africa.”

While this new find is the oldest genetic evidence of leprosy, there are other forms of evidence that date leprosy back further. Hippocrates, the Ancient Greek "Father of Medicine", wrote about a leprosy-like disease some 2,400 years ago. Researchers have even found a 4,000-year-old skeleton in India that shows deformations characteristic of leprosy.

The puzzle is not yet complete, it seems. However, with some further work, research like this could be used to help the 200,000 people who continue to be infected with the disease each year.

“Leprosy disappeared from Europe, but it used to be rampant in the Middle Ages, and we know very little about why this was the case. But unlike Europe, leprosy is still a problem in many endemic countries,” added Dr Andrej Benjak from the Global Health Institute at EPFL in Switzerland.

"Studying the past spread of M. leprae might help us identify mechanisms that still contribute to the persistence of this disease around the world.”

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