Leprosy plagued medieval Europe, causing nerve damage, muscle weakness, and permanent disabilities. Today, however, it has been almost eliminated (the last recorded case in the UK dates back to 1798) while the widespread availability of antibiotics means the global prevalence rate of the disease dropped from 21.1 cases per 10,000 people in 1983, to just 0.24 per 10,000 in 2014.
However, new DNA research from the University of Edinburgh and Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, has discovered the two bacterial species that cause leprosy in humans – Mycobacterium leprae and the recently discovered Mycobacterium lepromatosis – hidden in native British and Irish red squirrels, whether they displayed symptoms or not. ‘It was completely unexpected to see that, centuries after its elimination from humans in the UK, M. leprae causes disease in red squirrels,’ says Stewart Cole, Head of the Cole Lab at the EPFL Global Health Institute. ‘This has never been observed before.’
“The discovery of leprosy is worrying from a conservation perspective. We need to understand how and why it is acquired and transmitted so that we can better manage it in this iconic species”
The obvious concern – whether humans can catch the disease – is one the scientists are keen to play down. ‘There is no reason for panic,’ says the EPFL Cole Lab’s Andrej Benjak. ‘The risk of transmission to people is low because of their limited contact with humans, and hunting red squirrels is forbidden in most European countries.’
Instead, the concern is how to mitigate the worst impacts of the disease in squirrels themselves. Red squirrel numbers have dipped recently, predominantly thanks to the competition presented by their North American cousin, the grey squirrel (the Forestry Commission estimates only 140,000 reds in Britain, compared to over 2.5 million greys). ‘The discovery of leprosy is worrying from a conservation perspective,’ says Anna Meredith, Personal Chair in Zoological and Conservation Medicine at the University of Edinburgh’s Royal (Dick) School of Veterinary Studies. ‘We need to understand how and why it is acquired and transmitted so that we can better manage it in this iconic species.’
This was published in the January 2017 edition of Geographical magazine.
