Microbiologists at EPFL and the University of Edinburgh have discovered that red squirrels in Britain and Ireland carry the two bacterial species that cause leprosy in humans. Once rampant in medieval Europe, leprosy dramatically declined by the end of the Middle Ages for reasons that are still unclear. About a century ago, leprosy in Europe virtually disappeared, at least among humans. Examining diseased red squirrels from England, Ireland, and Scotland, scientists at EPFL and the University of Edinburgh have now discovered that the same bacteria that cause leprosy in humans also infect red squirrels. The work was published online on November 10, 2016 in Science. The article is titled “Red Squirrels in the British Isles Are Infected with Leprosy Bacilli.” Leprosy is an infectious disease that mainly affects the skin, peripheral nerves, the upper respiratory tract, and the eyes. It is caused by the bacteria Mycobacterium leprae and the recently discovered Mycobacterium lepromatosis. One of the most ancient diseases, leprosy has had an enormous social impact across multiple cultures throughout history. Largely controlled today thanks to antibiotics, there are still over 200,000 new cases of leprosy reported each year worldwide. A little-known fact is that leprosy also affects animals, such as armadillos, which have reportedly caused a few cases of animal-to-human (or "zoonotic") infections. Drawing from this evidence, the labs of Dr. Stewart Cole at EPFL and Dr. Anna Meredith at the University of Edinburgh carried out DNA tests on 110 red squirrels from England, Scotland, and Ireland. Some of these animals showed clinical symptoms of leprosy, while others did not; nonetheless, most were found to be infected with leprosy bacteria.
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