Up until now, the biggest threat to British red squirrels was thought to be competition from their grey cousins – and the squirrelpox virus they spread. But a recent study has shown that the majority also have to contend with leprosy.
The disease, which was prevalent in the Middle Ages, has long been wiped out in humans in Britain. But it appears that red squirrels are still highly susceptible to the two types of bacteria, resulting in swelling and hair loss to the ears, muzzle and feet.
Researchers from Lausanne’s Federal Institute of Technology (EPFL) joined forces with the University of Edinburgh to examine the DNA of red squirrels on the small island of Brownsea, off the south coast of Britain.
The study, presented in the journal Science, found that most were infected by at least one of the bacteria Mycobacterium leprae and Mycobacterium lepromatosis, even though many of the animals were not displaying symptoms. Despite leprosy being found earlier in Scottish red squirrels, the scale of the findings in Brownsea surprised researchers.
"The next logical step after this study would be to investigate the condition of red squirrels outside the British Isles, including Switzerland", one of the study’s authors, Andrej Benjak from EPFL, told the Swiss news agency SDA.
But Benjak also played down the risks to humans by leprous squirrels for the practical reason that there is limited contact between the two.
"Even if there is leprosy bacteria infection in red squirrel on continental Europe, the risk of transmission to humans is generally low", he said.
Red squirrel numbers in Britain have declined from a high of 3.5 million to fewer than 120,000 today. The decline has been largely blamed on habitat loss and the introduction of the North American grey squirrel last century. Greys are are bigger, can live in much denser populations and often carry the squirrelpox virus which is more harmful to reds.
swissinfo.ch with agencies