Why leprosy died out in Europe
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Leprosy was a scourge of medieval Europe. The image of the leper, covered with sores and face or limbs eaten away by infection, ringing a bell to announce his or her presence, remains powerful today.
Yet at the beginning of the 16th century, leprosy suddenly changed from being a common to a very rare disease in western Europe. Microbiologists have long been puzzled by this abrupt retreat. Did a genetic change make the bacteria less infectious and virulent? Was social change responsible? Or might the key factor be a change in human immunity to leprosy?
A remarkable genetic investigation, published in the journal Science, provides a partial answer. It turns out that DNA of Mycobacterium leprae extracted from medieval graves is nearly identical to that of the modern bacterium, which still causes about 200,000 cases of leprosy a year worldwide.
So the sudden decline of European leprosy 500 years ago is almost certainly not due to a loss of bacterial infectiousness or virulence. Social changes may have played a part but living conditions for most of the population were not that different in 1400 and 1600.
Researchers at the Ecole Polytechnique Fédérale de Lausanne in Switzerland, who played a leading role in the project, prefer an explanation based on host immunity. Many clues indicate that humans developed resistance to the disease, says Stewart Cole, head of the Global Health Institute at EPFL. Conditions were ripe for an intense process of natural selection, with a high prevalence of leprosy and the social isolation of the diseased.
“In certain conditions, victims could simply be pressured not to procreate,” Cole says. “In addition, other studies have identified genetic causes that made most Europeans more resistant than the rest of the world population.”
The leprosy study is the latest example of the way DNA extracted from ancient human remains is shedding light on the history of diseases. The researchers managed to obtain M leprae genomes from the bones of five medieval leprosy cases buried in Sweden (Sigtuna), Denmark (Odense and Refshale) and England (Winchester).
Forty per cent of all the DNA present in the tooth of a woman who died in a 1300s Danish leper colony was M leprae – an astonishingly high proportion, which enabled the scientists to sequence the bacterial genome directly rather than using laborious techniques that patch together degraded traces of ancient DNA.
Further investigation at the University of Tübingen showed that so much M leprae DNA had survived because the bacteria have thick cell walls rich in fatty acids that repel water and reduce damage. If the same is true for other pathogens, it may be possible to trace infections back hundreds of thousands of years.
Tall talk: how altitude and language are linked
The first good evidence of a link between geography and the way people speak has emerged from a study relating language structure to elevation above sea level.
The research by Caleb Everett of the University of Miami published in the journal PLoS One shows that “ejective consonants” – produced with an intense burst of air – occur mainly in languages spoken at high altitude. (They do not feature in Europe.)
Everett analysed the locations of 600 representative languages from around the world, 92 of which had ejectives. It turned out that 87 per cent of them are found in areas more than 1,500m above sea level, including the Andes, the Rockies, the South African plateau, the east African rift region and the Caucasus.
“This is evidence that geography does influence phonology – the sound system of languages,” explains Everett. “Ejectives are produced by creating a pocket of air in the pharynx [part of the throat] then compressing it.
“Since air pressure decreases with altitude and it takes less effort to compress less dense air, I speculate that it’s easier to produce these sounds at high altitude,” he says.
Because the speaker uses air from the pharynx, this may reduce the amount of air exhaled from the lungs and therefore reduce dehydration, he says.
The Himalayas and Tibet make up the only high-altitude region without ejective consonants in its native languages. This exception may be a consequence of the fact that Himalayan people tend to breathe faster than others living at high altitude – which might make ejective expression harder.
Putting ‘engineering’ at the heart of society
York University is not a place you would expect to put on a wide-ranging exhibition of engineering research. After all, it has no department or faculty of engineering. But over the coming week York and the Royal Academy of Engineering are collaborating to stage Engineering: Design for Living as part of the university’s 50th anniversary celebrations.
The ambitious show is an effort to extend the reach of engineering “to the heart of society”, as York vice-chancellor Brian Cantor puts it, and “demonstrate that it improves lives in many, often surprising, ways”.
The aim is to move beyond the traditional categories of mechanical, civil and chemical engineering – and portray engineering as an activity that pays little attention to academic labels and boundaries.
“Britain is a bit sniffy about engineering,” says Cantor, himself a fellow of the Royal Academy of Engineering. “Engineering is all around us … Important scientific and artistic, creative and transformative achievements could not happen without a significant input from engineering.”
High-tech microscopy is one fruitful field of collaboration. York biologists are working to develop instruments that vividly reveal what is happening to living cells.
“Microscopy is far more than simply looking down a light microscope and seeing a cell outline,” says Peter O’Toole, head of imaging and cytometry. “We can now explore cells in incredible multicoloured three-dimensional detail.”
Aerial 3D images are giving archaeologists a new understanding of the way landscape has shaped human behaviour – and vice versa – down the millennia. They can probe below the modern surface and see buried features that are not visible clearly from the ground.
One study focuses on satellite images of Saudi Arabia, probably one of the first places settled by our human ancestors as they moved out of Africa. “By understanding the development of the landscape over time, we can identify where archaeological material could be preserved, as well as reconstructing what the landscape may have looked like when the earliest humans were first dispersing from Africa,” says York archaeologist Robyn Inglis.
Closer to home, her colleague David Roberts is using ground-penetrating Lidar technology to show up earthworks in the Teffont area of Wiltshire. “We were able to find a large, rectangular anomaly, which was the site of a Roman shrine we were looking for,” he says.
Other York researchers are combining the wave properties of light – interference and polarisation – with computer analysis of surface shape for applications in biosecurity and surveillance. For instance, statistical models of human faces and light reflectance from skin make it possible to reconstruct a 3D face from a single 2D image.
Meanwhile, Cantor is preparing to move on from York after 11 years (to Bradford University) with many accomplishments to his credit but one slight failure. “I’m a bit disappointed that I leave the university without having managed to create an overt offering in engineering,” he admits.
“Engineering: Design for Living” runs June 22-26 at York’s Ron Cooke Hub. See http://yorkfestivalofideas.com