Red squirrels in the UK are having a pretty hard time at the moment.

Their numbers have been declining for years and they have been driven out of many British forests by rival American gray squirrels. But now there's a new threat: leprosy.

The disease was first detected in Scotland in 2014, but has since spread to other areas around the UK.

“We don’t know why it’s only red squirrels," says Anna Meredith from the University of Edinburgh. “We haven’t found it in any other species of squirrel yet. And we don’t really know how badly it’s affecting them and what impact it’s having on the population.”

But they are trying to find out.

Meredith is leading a new research project on Brownsea Island, just off the south coast of England.

Her team will monitor red squirrel numbers and will try to determine how leprosy is spreading around the population.

Brownsea Island off the south coast of England

Chris Lacey, National Trust.

“We are using an island because it creates a really nice environment to run a study. It’s contained and we know there’s a good population of around 200 squirrels,” she says.  

“But it’s also very important because it’s about the only place in England where red squirrels are left.”

The population elsewhere in the UK, Meredith says, has been devastated by the gray squirrel, which was introduced from North America toward the end of the 19th century.

Gray squirrels are larger, more aggressive and better at finding food. But crucially, they also spread a disease called squirrel pox, which is deadly to red squirrels.

“In the UK we consider [the red squirrel] a priority species for conservation,” Meredith says. “About 75 percent of the remaining red squirrels in the UK are in Scotland. There are very concerted efforts there to halt the spread of the gray squirrel.”

With the new threat of leprosy, and the existing threats from the gray squirrel, Meredith says something must be done to save the red squirrel.

“They are an iconic species and much loved by the British public,” she says. “It’s a real shame to lose any species ... and essentially lose it through the actions of people.”

“We introduced the gray squirrels. We have cut down a lot of the trees and destroyed the habitat where the native red squirrel lives. I think we have a moral obligation to try and limit some of that damage and reverse the change to save this very iconic species.”

A previous version of this story misstated where Anna Meredith teaches.

From PRI's The World ©2016 PRI