A mother and baby koala are seen Sept. 23 at the Sydney Wildlife World in Sydney, Australia. A study on koalas has found an unexpected consequence of habitat loss is a latent disease called chlamydiosis that can cause blindness, infertility and death in 50 to 90 percent of the creatures.

Cudlee Creek, Australia ? The koala, Australia’s star symbol, is dying of stress.

Koalas live in the rolling hills and flat plains where eucalyptus trees grow, because they need the leaves for both food and water.

But as people move in, koalas are finding themselves with fewer trees, researchers say.

The stress is bringing out a latent disease that infects 50 to 90 percent of the animals.

“Koalas are in diabolical trouble,” says researcher Frank Carrick, who heads the Koala Study Program at the University of Queensland. “Numbers show that even in their stronghold, koala numbers are declining alarmingly.”

The problem came to national attention in August, when the well-known Sam the Koala died during surgery to treat the disease, called chlamydia.

Sam captured the world’s attention during major wildfires in February, when she was photographed drinking from the water bottle of a firefighter in a smoldering forest.

Sam was in such obvious pain from chlamydia that veterinarian John Butler decided to operate. But her organs were too scarred to complete the surgery, and Sam was euthanized.

Chlamydiosis is a virus that breaks out in koalas in times of stress — like cold sores in humans — and leads to infections in the eyes and urinary, reproductive and respiratory tracts. It can cause blindness, infertility and death.

Deborah Tabart, chief executive of the Australian Koala Foundation, urged the government to follow up on Sam’s case by classifying koalas as a threatened species and implementing policies to preserve their habitat. Her organization named September “Save the Koala” month, with the theme “No Tree, No Me.”

The United States already considers the koala a threatened species.

And the Australian Koala Foundation estimates there are fewer than 100,000 koalas left in Australia, down from the millions at the time European settlement started in the late 1700s.