Why it may be necessary to kill a sizeable population of Australia's koalas

As our biosphere continues to collapse and man-made greenhouse gases continue to assault our only home, we will be confronted with more and more catastrophes that we will just not want to face.

Australia’s adorable koala is suffering  horribly from an exceptionally painful and often lethal ancient pathogen. The iconic marsupial is being killed in large numbers by chlamydia, a sexually transmitted disease spreading exponentially through koala habitat.

With humans chlamydia is a common sexually transmitted disease easily treated with antibiotics. A different chlamydia strain infects koalas, and it too is spread sexually and is creating a devastating epidemic. Experts suspect the total number of koalas in Australia, is likely to be somewhere between 50,000 and 100,000. In some parts of Australia, koala infection rates are as high as 90%. It is not that chlamydia is not found in other species, but the infection is usually at very low levels. Experts do not know why it is affecting the koala so seriously. Chlamydia affects male and female koalas, and even the very young babies known as  joeys. The joey contracts the bacteria from their mother, by suckling in her pouch. It also appears to be transmissible via urine.  

Symptoms include blindness and infertility and it can be fatal. Visible signs of infection include red eye, and a condition named "dirty tail," caused by urinary tract infections and incontinence. Dirty tail is an awful experience for the marsupials. The urinary tract gets inflamed and expands substantially. It is incredibly painful. They get discharge and many koalas die a horrible death as a result.

Koalas can’t be treated with antibiotics, at least not on a mass scale, because their gut bacteria, which is essential to digesting Eucalyptus leaves which is what they eat throughout their lifespan. Systemic antibiotics, will kill this gut bacteria starving and dehydrating the koalas.  

BBC reports on the suggestion of euthanizing a sizable population of the infected koalas.

A large scale round up and bringing them to hospitals is too resource intensive and not feasible explains Professor David Wilson, Head of Infectious Disease Modelling for the Burnet Institute:

Instead, he has come up with a controversial strategy. “My suggestion is this: the population is in decline. The way we can increase the population is, paradoxically, we should kill some of them.” 

“They’re transmitting chlamydia to each other and many of them can’t be healed. These koalas are in a lot of pain and if they’re out of the time-range of antibiotics being effective; the humane thing to do is probably to euthanize them.”

Wilson argues a strategic cull now would help the koala population begin to bounce back in the next 5 to 10 years.

The Abstract from David Wilson’s study titled “THE PARADOX OF EUTHANIZING KOALAS (PHASCOLARCTOS CINEREUS) TO SAVE POPULATIONS FROM ELIMINATION” was published in the Journal of Wildlife Diseases. 

Koala (Phascolarctos cinereus) populations in the wild are in sharp decline in Australia due to deforestation, road accidents, dog attacks, and disease from infection with sexually transmitted Chlamydia spp. Severely diseased koalas that are captured are euthanized for humane reasons because antibiotics are not effective. Paradoxically, we propose that euthanizing more koalas could help to increase koala population numbers. We investigated the potential impact of systematically euthanizing diseased koalas. Using data from a well-studied koala population, and an individual-based computer simulation model, we predict that such a program would result in a larger population of koalas after 7 yr than would exist without the program. If terminally diseased and sterile koalas are euthanized and other infected captured koalas are given antibiotics, chlamydial infection could be eliminated and population growth observed after 4 yr. The practical implementation of such a program would be facilitated with further development of tools to diagnose infection and internal disease in the field.

There is some positive news, clues from the koala genome has advanced promising vaccines.

“End stage disease is hard to stop but if we get them early on, we might have a better chance,” says Timms.  So far the team has completed eight trials including six in the lab, and two in the field. Timms says they are still testing but the results look promising.

The vaccine is something that works and it is something we can do now

Early trials have found the vaccines effective at stopping koalas picking up the infection. They have also found that despite strains of chlamydia varying across the country, it is possible to develop a vaccine that combats this. And they have managed to make the vaccine administrable in one dose rather than three.

“While the vaccine’s not perfect, we’re catching koalas all the time now. We should be vaccinating them now. Not waiting 10 or 20 years.”

Disease is not the only threat to the survival of the species. There are native predators that include goannas, dingoes, predatory birds and pythons. Humans pose the most risk to koala populations. Humans hunted koalas for their pelts and this practice was only stopped in the late 1930s. Today, koalas face excessive habitat loss due to urban and agricultural development in the region, forcing them to live in smaller areas and closer to human populations. As many as 4,000 koalas are killed each year by run-ins with dogs and cars. Isolated populations inbreed.

Their brains are quite small, they get stressed easily and are confused when their habitat changes such as increasing temperatures due to climate change. Selective tree harvesting in their habitat eliminates the tree that the Alpha male needs to survive (think “Home Tree” in Avatar) causing it to wander in confusion while leaving its range with the females left stunned and lost to fend for themselves. They also have travel pathways that they use and human disturbance of that pathway will cause severe stress and confusion.

A threat also comes in the form of a koala retrovirus, which, like HIV in humans, suppresses a koala's immune system.

Climate change is also taking a toll on the koala’s diet of eucalyptus leaves. The leaves provide the main moisture intake to the koala in a very dry environment. Studies have shown that Eucalyptus trees are adapting to climate change so far. But that does not necessarily mean that this is good news for the Koala. Because it is not about the right Eucalyptus species but in many cases it comes down to the right tree. Research has shown that koalas choose to visit trees with leaves that contain high concentrations of nutrients and lower toxins.

The koalas desperately hug trees to stay cool as greenhouse gases assault the Australian continent with blistering heat waves. Measurements of the temperatures of the tree trunks showed that, on days as hot as 102 F, they were up to 12.6 degrees cooler than the air.  

Wildlife Bayside reports:

Climate change could have long-term negative impacts on the suitability of leaves for koalas. Research by Stalenberg (2010) suggests that koalas need a diversity of tree species with varied quality foliage so they can pick and choose their foods. This need for diversity may become even more important with climate change as a choice of trees will provide koalas with the capacity to alter their feeding patterns to respond to changing leaf chemistry and maintain a balanced diet over time.

While widespread eucalypt species adaption to climate change is good news but for the koala to survive it will still depend upon forest diversity and leaf quality.