Koalas die of chlamydia, and climate change makes it worse

For koalas, uncontrolled chlamydia can cause blindness and painful cysts in an animal’s reproductive tract that can lead to infertility or even death.

Worse still, the antibiotics used to treat the disease can destroy the delicate gut flora that koalas need to consume their staple diet of eucalyptus leaves, leading some to starve even after being cured.

The disease can also spread quickly.

In 2008, there was a “very, very low prevalence of chlamydia,” around 10%, in the koala population in Gunnedah, a rural town in northeastern New South Wales, according to Mark Krockenberger, professor of veterinary pathology at the University. from Sydney.

By 2015, that number had risen to 60%. Now about 85% of that koala population is infected with the virus, Krockenberger said.

“If you think about it, that is no longer a viable population due to infertility. Almost all women infected with chlamydia become infertile within a year, maybe two years at the most … Even if they survive, they are not reproducing.” . he said.

Experts say situations like Gunnedah’s are developing among Australia’s koala populations, threatening populations that are already vulnerable to worsening wildfires and habitat loss due to deforestation.

Scientists are now testing chlamydia vaccines to protect animals.

“We are at very high risk, if this vaccine strategy doesn’t work … of localized extinctions,” Krockenberger said.

Are koalas endangered in Australia?

There are few Australian animals more iconic than the koala.

The fluffy-eared gray marsupial, which eats leaves from the eucalyptus tree and carries its young in its pouch, can only be found in Australia and is regularly seen in cultural performances of the country.

But koalas face a number of threats to their survival. In addition to disease, marsupials suffer from habitat loss and are often attacked by wild dogs and run over by cars.

The koala is listed as “vulnerable” on the Red List of the International Union for Conservation of Nature (IUCN), which lists species at risk of extinction. The IUCN says there are between 100,000 and half a million koalas in the wild, but the Australian Koala Foundation says the number is closer to 58,000.
Confusion over the size of Australia’s koala population inspired the government to commit AU $ 2 million ($ 1.47 million) last year to a national koala census to find out where they are and how many are left.
The country’s koala population suffered severe losses during the catastrophic 2019 wildfires, which destroyed more than 12 million acres (48,000 square kilometers) of land across New South Wales alone.
The fires killed or displaced nearly 3 billion animals, according to the World Wide Fund for Nature (WWF). That figure includes more than 60,000 koalas that died, lost their habitat or suffered injuries, trauma, smoke inhalation and heat stress from the flames.
A koala named Paul from Lake Innes Nature Reserve recovers from his burns in the ICU at Port Macquarie Koala Hospital on November 29, 2019, in Port Macquarie, Australia.
In mid-2021, an Australian government report on the conservation status of koalas recommended the status of the animal be changed to “in danger” in Queensland, New South Wales and the Australian Capital Territory, as a result of rapidly declining populations in those areas. In some regions, the report found that populations had nearly halved in just 20 years.
The Australian government is drafting a National Koala Recovery Plan which will be reviewed in December 2021 before potentially becoming law in 2022.

But Deborah Tabart, president of the Australian Koala Foundation, says much more needs to be done to protect koalas and their habitat across the country, warning that marsupials could disappear in three generations.

“We want a law to protect koalas,” he said. “If you are really serious about protecting this species, you will have legislation that is effective and that means protecting the trees,” he said.

Activists say it would be similar to the Bald Eagle Act in the United States that protects the country’s national emblem from threats to its population and habitat.

How is chlamydia spread?

When faced with threats to the koala’s habitat and food supply, chlamydia can seem like a secondary problem.

But with the numbers dwindling, experts said reproduction has never been more important.

There are two varieties of chlamydia in Australian koalas, one of which, chlamydia pecorum, it is almost entirely responsible for the most severe cases of the disease in the population.

An article published in September 2020 in FEMS Microbiology Reviews said that the most dangerous strain of Chlamydia may have originated in domestic cattle brought to Australia by European colonizers in the 19th century.

The disease spreads in koala populations through reproduction and mating-related social behavior, although joeys, baby koalas, can contract the disease from their mothers.

According to the University of Sydney, infection rates in some mainland koala populations in Queensland, New South Wales and Victoria can be as high as 100%, making them completely infertile.
Highlighting the lethal potential of the virus, a study in the Journal of Applied Ecology In March 2018 it found that of 291 koalas examined over four years, 18% had died of chlamydia or related complications.

The disease was the second leading cause of death, after animal attacks.

Climate change is compounding the problem

The climate crisis has made Australia more vulnerable to devastating wildfires, such as those observed in 2019, as well as drought and heat waves. It also makes koalas more susceptible to disease.

According to Australia’s leading scientific body, the Commonwealth Scientific and Industrial Research Organization (CSIRO), the country has already warmed up about 1.44 degrees on average since 1910.

The Australian government report said that when marsupials are exposed to unusually stressful environmental conditions, including “hot weather, drought, habitat loss and fragmentation,” chlamydia spreads more rapidly through their population.

A sign warning motorists about koalas stands in front of a burned bush near the town of Bilpin, New South Wales, Australia, Sunday, Dec. 29, 2019.

Experts say they have witnessed similar rapid outbreaks of disease in the wild. Krockenberger said that in his Gunnedah sample population, a series of heat waves and droughts in 2009 and 2010 preceded a doubling of chlamydia cases.

Peter Timms, a professor of microbiology at the University of the Sunshine Coast in Australia, said that once koalas’ stress hormones rise due to environmental problems, infections often progress from a relatively minor problem to a “more serious one.”

He said a combination of habitat loss and climate change is causing koalas to be “chronically stressed,” depressing their immune systems.

“All of that leads to a poor response to chlamydia. It leads from low-grade chlamydia infections to more serious illnesses,” he said.

“That is what we are doing to them. And we are doing it on all fronts.”

Chlamydia Vaccine Trials for Koalas

But help could be on the way for Australia’s koalas.

A chlamydia vaccine, developed by researcher Timms over the last decade, is being tested among the country’s koala population as a way to protect animals from serious infections.

Control trials are underway to test the effectiveness of the vaccine in small groups of koalas, often around 20 or 30 at a time, Timms said. The current trial is the largest yet, with 400 koalas.

Some koalas are vaccinated when they are brought to veterinary hospitals with complaints other than chlamydia, while others are vaccinated as part of coexisting conservation efforts, he added.

“We know that the vaccine can reduce the rate of infection,” said Timms. “It doesn’t reduce it to zero. There are no vaccines that do that, but it negates the burden of infections.”

He said that while the process is expected to reduce the infection rate, it is difficult to monitor the spread of chlamydia in a wild population.

A koala is vaccinated against chlamydia at the Australia Zoo Wildlife Hospital in Queensland, Australia, on October 15.

Krockenberger of the University of Sydney, which is involved in a separate vaccine trial, said the purpose of the drug is not to reverse the progress of the disease in individual koalas. “Once they are chronically infected, they can often live reasonably happily, they just can’t reproduce,” he said.

Instead, he said the hope is that by reducing infectivity levels in koalas with chlamydia, researchers will be able to prevent the virus from spreading to new hosts and thus maintain a breeding population.

“We also hope that unaffected animals, when vaccinated, will be more resistant to contracting the infection,” he said.

Timms said that once the vaccine is proven safe and effective, he hopes to roll it out to Australia’s wildlife hospitals to vaccinate any koalas that pass through their doors.

He said people often ask him how he’s going to vaccinate “the last koala in the last tree” against chlamydia, to which Timms replies that “he won’t even try.” All you can do is try to save as much of the population as possible.

After all, “these are wild animals,” he said.


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