The Vital Link: Understanding Koala Health and Conservation
By Dr Jane Barker
The health of koalas is at the forefront of their conservation. Ensuring they are healthy will make the difference between survival and extinction. Science is developing a deeper understanding of koala health and what is needed for them to thrive in the wild in Australia.
Koalas are uniquely adapted to thrive exclusively on the leaves of the eucalyptus. These leaves are not only low in nutrients but also tough and fibrous, and contain toxins poisonous to many animals. The koala has evolved a specialist digestive system to be able to break down, digest, detoxify and extract as much nutrition from this diet as possible. The hind gut has been adapted to this diet. Relative to its size, it is one of the longest among mammalian species.
Gut Bacteria
Dr Jackie Reed, the expert koala vet with Friends of the Koala, explains that "the health of the koala is all down to gut bacteria."
Every mammalian gut contains the bacteria needed to digest the food to which they are adapted. This soup of bacteria is known as the gut biome.
Koalas have a unique set of bacteria in their guts that are capable of breaking down the tough fibres in eucalyptus leaves. These bacteria ferment the leaves in the koala's hind gut, breaking down the lignin, releasing the nutrients and removing toxins, ready for absorption. Large amounts of low nutrient leaves need to be eaten every day. In Australia, eucalyptus forests form around 2/3 of the natural forest. There are around 900 species of eucalypt trees, each adapted to their ecological environment, but koalas will only eat around 40 of these. In addition to this, the koala's microbiome is adjusted to enable them to digest only those eucalypts growing in their own local environment.
“Koalas need to have very specific bacteria according to what they eat, and that depends on their locality. So northern koalas have a very different gut biome than southern koalas. Maintaining a healthy gut biome is essential to their survival. If they get gut dysbiosis, the koala will try to restore their gut biome through eating dirt, bark or medicinal leaves. If they can’t do that, they may die.”
The mother koala transfers intestinal microflora to the joey at around 22 weeks by producing "pap”, modified fecal material, so the joey has the gut biome essential to its survival in the ecological environment it is born into.
A healthy gut biome plays a critical role in maintaining the health of the koala by aiding with digestion and absorption. Additionally, it has an effect on the koala's immune system, modulating its response to pathogens and controlling inflammation. Conversely, disruption of the gut biome can lead to gut dysbiosis, resulting in inadequate digestion of eucalyptus leaves and a compromised immune system, making it more prone to infection.
Dr Reed says that the koala is a very finicky eater, and its gut biome is very fragile. Gut dysbiosis is a condition where the koala loses condition due to malnutrition, develops diarrhoea and dehydration, and is prone to infection. Dr Reed explains that being an expert koala vet is essential because koala health is so complicated. Koalas are easily stressed, such as by habitat loss, barking dogs or inadequate diet. This can cause gut dysbiosis, which may also be caused by the use of antibiotics and steroids. Gut dysbiosis may lead to immune suppression which, together with koala retrovirus infection, another disease in the koala health equation, can exacerbate chlamydia or other infections.
Chlamydial Infection
Chlamydial disease is a significant threat to the survival of koalas. Caused by the bacteria Chlamydia Pecorum, chlamydial disease is endemic among koala populations, with studies showing between 60% - 80% testing positive in different areas. Chlamydia is primarily transmitted through sexual contact but may also be transmitted from mother to joey.
Chlamydia can affect the eyes, causing keratoconjunctivitis, leading to scarring and loss of vision. When the infection affects the urinary tract, it may cause severe pain, frequent urination and incontinence. Incontinence causes "wet-bottom”, a condition when there is urine staining of the rump with possible skin ulceration and infection. Infection in the genital tract causes inflammation and scarring, leading to infertility. In female koalas, reproductive cysts may develop.
“The ones that suffer most are the females who get reproductive tract infections leading to sterility. If we don’t have fertile females out there to reproduce, what hope is there for the species?”
Chlamydia may be exacerbated by co-infection with koala retrovirus, which causes immune suppression, increasing the risk of contracting chlamydia and progressing onto severe disease. While antibiotics are effective in early onset disease, their effect on the microflora of the gut may be devastating, leading to gut dysbiosis. The use of probiotics is being investigated.
Vaccination Against Chlamydia
The great hope for chlamydia is an effective vaccine. The complex biology of the koala immune system and the intracellular nature of the bacteria have presented challenges, and many years of work have gone into developing a vaccine. With fears that without drastic intervention by 2050, there will be no koalas living in the wild, an effective vaccine may be the miracle that is needed. There are two vaccines currently being trialed, and the efficacy of the vaccine is looking optimistic, offering a level of protection against new disease and prevention of recurrent disease developing in koalas already treated for chlamydia. However, further research needs to be undertaken.
The Friends of the Koala hospital is involved in research together with the University of the Sunshine Coast in clinical trials looking at vaccine efficacy, and is starting to deliver vaccines to koalas admitted to the hospital.
The barriers to the survival of koalas are complex and interrelated, leading to vicious cycles of stress, gut dysbiosis and increased levels of infection. Treating infections with antibiotics, in turn, leads to gut dysbiosis, further lowering immunity.
“Antibiotics are all we have to treat chlamydia until the vaccine is available. Then we will not see chlamydia, we will not need to use antibiotics, and not cause gut dysbiosis. Happy Days!”
The hope has to come through meeting each obstacle head-on, which is what Friends of the Koala are attempting to do by:
Creating corridors of koala trees linking existing koala habitat and increasing the area of forest available for feeding. This also reduces the movement of koalas into urban areas seeking food and therefore reducing the risk of trauma from vehicles and dogs.
Treating sick and injured koalas and returning them to their familiar wild habitat.
Education and advocacy for change in environmental laws and funding for koala conservation.
Contributing towards scientific research to optimise the koala's chances through exploring genetic diversity, the koala gut biome and the use of vaccines.
Australia has a very poor history of the loss of species since colonisation. Often these species were unique to Australia, found nowhere else in the world. Koalas are threatened on all fronts from deforestation and land clearing causing habitat loss, climate change leading to natural disasters from floods to fires and the fears of rising temperatures, and a devastating disease decimating the wild population. Seeing koalas in the wild brings great joy. These beautiful creatures are now endangered. The time to act is now, or else there will be no tomorrow for our most iconic mammal.
To learn more about koalas, the threats to their survival, and breakthroughs in scientific understanding of koala health issues:
Explore the Friends of the Koala website
Read "A Koala Life - Up Close and Personal," a fact sheet published by The Department of the Environment and Natural resources.
Read "Koala - A Life in Trees" by Danielle Clode
Review "Helping koalas battle disease – Recent advances in Chlamydia and koala retrovirus (KoRV) disease, understanding and treatment in koalas" by Bonnie L Quigley and Peter Timms. [Link to the article]