Researchers have found a population of koalas that could be vital for stabilising the koala population.

Scientists from the University of Adelaide say they've found what could be the last Australian koalas totally free of chlamydia, according to a study published recently in the journal Nature Scientific Reports.

Chlamydia is rampant in the primary koala habitat in New South Wales and Queensland on the country's eastern coast. A 17-year study published in 2017 characterised the koala population as in catastrophic decline.

The disease is exacerbated by the stress that koalas feel from habitat loss, and the Australian government lists the tree-dwelling marsupials as "vulnerable."

The sexually transmitted bacterial infection, which causes blindness, female infertility and death, threatens to wipe out the species, according to the Australian Koala Foundation.

"This last large, isolated chlamydia-free population holds significant importance as insurance for the future of the species," Jessica Fabijan, an author of the study and a Ph.D. student at the University of Adelaide, said in a news release. "We may need our Kangaroo Island koalas to re-populate other declining populations."

Researchers captured (and later released) 75 wild koalas from the Mount Lofty Ranges outside the southern city of Adelaide. They compared them with 170 koalas from Kangaroo Island, about 8 miles off the coast of southern Australia.

Veterinarians tested both groups for Chlamydia perocum and koala retrovirus.

Of the koalas from the mainland, 47.5% had chlamydia, but not one of the koalas from the island had the infection or signs of the disease.

On Kangaroo Island, the researchers estimate the koala population at about 50,000 and say that growing this koala population could help offset losses elsewhere.

"Future-proofing South Australia's koala health is paramount to ensuring the survival of the species in Australia, given the marked decline in the eastern states," said Brenton Grear, a spokesman for the South Australian Department for Environment and Water.

Scientists are looking at a number of ways to push back against the chlamydia epidemic.

In 2018, researchers announced that they had mapped the koala genome, fueling hopes for a vaccine against chlamydia.

"There are current trials of a Chlamydial vaccination in northern koalas to protect them from infection, but it is an uphill battle," Fabijan said.

For now, the koalas on Kangaroo Island are the species' best hope.