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Red squirrels in UK, Ireland carry leprosy
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Researchers discovered that red squirrels living in the United Kingdom and Ireland carry leprosy bacteria, but say there is little risk of transmission to humans.
The protected squirrel species harbors a strain of Mycobacterium leprae akin to one that circulated in humans in medieval Europe, but was eradicated centuries ago. They also harbor a strain of the recently discovered M. lepromatosis, according to Anna Meredith, PhD, professor in the University of Edinburgh’s Royal (Dick) School of Veterinary Studies, and colleagues.
“The discovery of leprosy in red squirrels is worrying from a conservation perspective but shouldn’t raise concerns for people in the U.K.,” Meredith said in a news release.
According to WHO, around 212,000 new cases of human leprosy were reported worldwide in 2015. The ancient disease can be cured with multidrug therapy and is now mostly a concern in low- and middle-income countries. The only British cases occur in patients who have lived in one of the countries where it is endemic, Meredith and colleagues noted.
While investigating a potential leprosy outbreak among red squirrels in the U.K., they collected samples from squirrel cadavers in Scotland and England, where evidence of leprosy was observed, and in Ireland, where there had been no signs of infection. They analyzed 172 tissue samples from 13 squirrels with signs of leprosy and 101 with no signs, using PCR to screen for M. leprae and M. lepromatosis DNA.
Red squirrel with small leprosy lesion on its ear.
Source: Karen van der Zijden
All 25 red squirrels tested from Brownsea Island in southern England carried a type of M. leprae closely related to two strains from medieval England and Denmark, including one originating from the skeleton of a leprosy victim buried 730 years ago in the nearby city of Winchester. Just eight of the 25 had clinical signs of the disease such as swelling and hair loss on the ears, muzzle and feet.
According to Meredith and colleagues, the strain also is highly related to one that is endemic in nine-banded armadillos in the southern United States.
Nine squirrels from Scotland, Ireland and the Isle of Wight off the southern English coast — including six with clinical signs — harbored a strain of M. lepromatosis related to human strains from the Caribbean and Mexico. Overall, 21% of the red squirrel cadavers studied without clinical signs of leprosy and 100% of those with clinical signs harbored leprosy bacilli.
It was not possible to distinguish between M. leprae and M. lepromatosis infections during post mortem inspection the way it is in human cases, Meredith and colleagues wrote. They said their research proves leprosy can survive for a long time without humans as a reservoir.
“Finding M. leprae in red squirrels in England was unexpected because leprosy was eradicated from the British Isles several centuries ago,” they wrote in Science.
According to Meredith and colleagues, the red squirrel population in the U.K. is down to about 140,000, decimated by habitat loss, squirrel poxvirus and competition with more than 2.5 million gray squirrels introduced from North America.
Meredith and colleagues said it was unclear whether leprosy was also contributing to the decline, or even how the squirrels became infected in the first place.
“We need to understand how and why the disease is acquired and transmitted among red squirrels so that we can better manage the disease in this iconic species,” she said in the release. – by Gerard Gallagher
Disclosures: The researchers report no relevant financial disclosures.
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