LONDON – Britain's red squirrels – under threat from their promiscuous and disease-bearing North American cousins – may finally have some good news.

Scientists said Wednesday the rust-tailed rodents were showing signs of resistance to a devastating disease borne by their American counterparts.

Red squirrels are vulnerable to the squirrelpox virus, unlike the gray squirrel, which was brought to Britain from North America by Victorian landowners more than a century ago. Red squirrel numbers have plummeted, prompting scientists to fear they would be wiped out in Britain.

However, researchers with the Zoological Society of London and elsewhere discovered that some red squirrels have developed a natural immunity to the disease.

“This finding is the first sign of hope in the long struggle to save the species from extinction in the U.K.,” said Anthony Sainsbury, a researcher at the zoo whose findings were published in the peer-reviewed journal EcoHealth Wednesday. He and other scientists examined about 500 squirrels that had died. Eight of them had survived the virus before their deaths and developed an immunity to the disease, something Sainsbury said had never been detected before.

“Immunity to the squirrelpox virus should give red squirrels a fighting chance against the gray invaders,” he said.

Experts believe there are less than 140,000 red squirrels in the United Kingdom – while gray squirrels number in the millions.

Britons have launched several programs intended to save the red squirrels, immortalized by British children's author Beatrix Potter as the engaging, nut-obsessed “Squirrel Nutkin.” Conservation groups have floated various ideas, including special red squirrel reserves and a sterilization program to put a brake on gray squirrel's aggressive breeding. Sainsbury said scientists now have to further study how widespread the immunity is before working to develop a vaccine to protect the surviving population.

Stan Boutin, a professor in the Department of Biological Sciences at the University of Alberta, read the paper and said he thought that while the evidence was suggestive, further investigation was warranted.

Gray squirrels will still dominate their red counterparts, according to Rudy Boonstra, professor of Physiology and Zoology at the University of Toronto, calling them “competitively superior to the red squirrel.”

Red squirrels are native to most European countries and parts of Asia. It's most threatened in Britain but has also been struggling to survive in parts of Italy, where the gray squirrel has also been introduced.

Associated Press Writer Meera Selva contributed to this report.

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