(CNN) – A silent killer is spreading through Australia’s koala population, posing a threat that wildlife experts say could kill the iconic marsupial across vast areas of the country.
The culprit is chlamydia, a sexually transmitted virus that infects more than 100 million people a year worldwide and may cause infertility in humans if left untreated.
In the case of koalas, uncontrolled chlamydia can cause blindness and painful cysts in the 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.
Chlamydia, a rapidly spreading disease
The disease can also spread quickly.
In 2008, there was a “very, very low prevalence of chlamydia” – about 10% – in the koala population of 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’s no longer a viable population due to infertility. Virtually all chlamydia-infected females become infertile within a year, maybe two years at the most … Even if they survive, they don’t reproduce,” he explained .
Experts say situations like Gunnedah are brewing among koala populations across Australia, threatening populations that are already vulnerable to worsening wildfires and habitat loss due to deforestation.
Scientists are now testing chlamydia vaccines to protect animals.
“If this vaccination strategy does not work, we are at great risk of localized extinctions,” Krockenberger said.
Are koalas endangered in Australia?
There are few Australian animals more iconic than the koala.
This gray fluffy-eared marsupial, which feeds on eucalyptus leaves and carries its young in its pouch, is only found in Australia and regularly appears in cultural representations 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.
The koala is listed as “vulnerable” on the Red List of the International Union for Conservation of Nature (IUCN), which lists species as endangered. 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 the 58,000 copies.
Confusion over the size of Australia’s koala population inspired the government to allocate A $ 2 million (US $ 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 alone in New south Wales.
The fires killed or displaced nearly 3,000 million animals, according to the World Wide Fund for Nature (WWF). That number includes more than 60,000 koalas that died, lost their habitat or suffered injuries, trauma, smoke inhalation and heat stress from the flames.
In mid-2021, an Australian government report on the conservation status of koalas recommended change the animal’s status to “endangered” in Queensland, New South Wales and the Australian Capital Territory, as a result of rapid population declines in those areas. In some regions, the report found that populations had nearly halved in just 20 years.
The Australian government is developing a National Koala Recovery Plan which will be reviewed in December 2021 and could become 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 Koala Protection Law,” he said. “If you are really serious about protecting this species, you have to enact legislation that is effective, and that means protecting the trees,” he added.
Activists say it would be similar to the United States’ Bald Eagle Act, which protects the country’s national emblem from threats to its population and habitat.
How is chlamydia spread?
In the face of threats to the koala’s habitat and food supply, chlamydia might seem like a secondary problem.
But with their numbers declining, experts say that reproduction has never been more important.
There are two varieties of chlamydia in Australian koalas, one of which, chlamydia pecorum, 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 notes that the most dangerous strain of Chlamydia may have originated in the domestic cattle brought to Australia by European settlers in the 19th century.
The disease spreads in koala populations through reproduction and mating-related social behavior, although the young – 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 reach 100%, which makes them totally infertile.
Highlighting the lethal potential of the virus, a study published 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 exacerbates the problem
The climate crisis has made Australia more vulnerable to devastating wildfires, such as those in 2019, as well as drought and heat waves. It’s also making 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 a few 1.44 degrees on average since 1910.
The Australian government report notes that when marsupials are exposed to unusually stressful environmental conditions, such as “heat, drought, habitat loss and fragmentation,” chlamydia spreads more rapidly among its population.
Experts claim they have witnessed similar rapid outbreaks of the 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 go from being 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 moves them from low-grade chlamydia infections to more serious diseases,” 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 past decade, it 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 efficacy of the vaccine in small groups of koalas, often about 20 or 30 at a time, Timms said. The current trial is the largest to date, with 400 koalas.
Some koalas are vaccinated when they are brought to veterinary hospitals with ailments other than chlamydia, while others receive the vaccine 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 greatly reduces the burden of infection.”
He said that while the process is expected to reduce the infection rate, it is difficult to control the spread of chlamydia in a wild population.
Krockenberger of the University of Sydney, who is involved in another vaccine trial, said the drug’s goal is not to reverse the progress of the disease in individual koalas. “Once they are chronically infected, they are usually able to 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 get it to wildlife hospitals across Australia to vaccinate 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’s not even going to try.” The only thing you can do is try to save as much population as possible.
After all, “they are wild animals,” he says.
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