Bonnie Chaban¹, Vanissa A. Ong¹, Jonathan Hanger², Peter Timms¹

¹Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs, Queensland, 4556, Australia

²Endeavour Veterinary Ecology, 1695 Pumicestone Road, Toorbul, Queensland, 4510, Australia

Koala retrovirus (KoRV) is a new virus that has created new opportunities for retroviral research and new challenges for koala conservation. There are currently two major types of KoRV; KoRV-A, which we believe has added itself to koala DNA and is now passed from parents to joeys in the northern part of Australia, and KoRV-B, which appears to be passed from koala to koala like other viruses in the environment. KoRV is in the same virus family as human immunodeficiency virus (HIV, leading to AIDS in people) and feline leukemia virus (FeLV, which causes cancer in cats). To understand how much of each KoRV type is present in Queensland, what it might be doing to koalas and how it might be spreading between koalas, we studied a wild Moreton Bay koala population of 290 koalas over a five year period. We found that all the koalas we tested were KoRV-A positive (100%) and they all had the same surface protein (meaning KoRV-A is not changing much in this group). By comparison, we found that only 24% of koalas tested KoRV-B positive and within these koalas, we found 21 different versions of the surface protein (meaning KoRV-B is actively changing and adapting as it moves from koala to koala). When we looked at whether having KoRV made a difference to getting another serious disease, we found significant links between koalas having KoRV-B and developing chlamydial disease and/or cancer. So, to figure out how KoRV-B was being spread through the population, we followed 49 adult koalas over several years, as well as 25 new joeys being born into the group. We found that if a koala was KoRV-B negative when he/she became independent, he/she only had a 3% chance each year of getting KoRV-B from another koala. However, we found that if a koala was KoRV-B positive when she started having joeys, all her joeys would have KoRV-B (100%) and if she was KoRV-B negative when she had a joey, her joey would be KoRV-B free (0%). This told us that mothers infecting their joeys is the most significant way KoRV-B is being spread through the group. Overall, this study helped us learn that KoRV-B is the virus type that is contributing to chlamydial disease and cancer in the koala population, making it an imminent threat to this already vulnerable species. We also learned that if we can stop KoRV-B spreading from mother-to-joey, we can have a major impact on how much KoRV-B infection is in the wild. Both of these outcomes are now helping our group develop the first KoRV vaccine to combat this new threat to koala health.

Written by Bonnie Chaban

In the late 1800s and early 1900s, habitat loss, bushfires and hunting for the commercial fur trade led to widespread population declines and localised extinctions of koalas across Victoria.

Mainland koala populations were later re-established throughout the state by translocation of koalas from island populations, which were founded by small numbers of koalas in the late 1800s. As a result, most Victorian koala populations have relatively low levels of genetic diversity.

Genetic diversity is important for the long-term persistence of a species as it provides populations with the capacity to cope with pressures such as disease or climate change. Due to a range of interacting factors, reduced genetic diversity is known to increase a population’s chance of extinction.

Using DNA sourced non-invasively from koala scats, research conducted at Federation University’s Churchill campus (https://link.springer.com/article/10.1007/s10592-018-1049-8) has confirmed that the South Gippsland koala population is genetically distinct and significantly more diverse than Victorian populations established by island koalas. Koalas in South Gippsland were found to have an additional 38 nuclear DNA allele variants and seven extra mitochondrial DNA sequence variants not present in the island populations assessed.

Relative to other Victorian koala populations, greater genetic diversity may provide South Gippsland koalas with an increased chance of survival in the face of future pressures. Conserving the South Gippsland koala population and its genetic diversity are therefore highly important for the long-term survival of koalas in Victoria.

The South Gippsland koala population currently exists in highly fragmented habitat. Population fragmentation and isolation are major threats to the genetic diversity that remains in the koalas of South Gippsland. Improving habitat quality and its connectivity in the region are paramount to the conservation of koalas in South Gippsland and the greater genetic diversity that they have retained.

Written by Faye Wedrowicz

A series of recent studies by researchers at the University of the Sunshine Coast (USC) in collaboration with a range of partners across the country have revealed that (i) koalas are not the only marsupial hosts of chlamydial infections and that (ii) Chlamydia pecorum, the major pathogen of the koala, is not the only chlamydial species that can be found. 

In a report recently published in the journal, Scientific Reports (https://www.nature.com/articles/s41598-017-13164-y), the researchers found that C.  pecorum, could also be detected in common brushtail possums, squirrel gliders and spotted tail quolls in Queensland, New South Wales and, interestingly, Tasmania. No evidence of the characteristic signs of chlamydial disease could be found in these animals, however. How common these infections are and what impact they have for animal health is currently unknown but it does raise interesting new questions about the origin and relationships of these C. pecorum strains to those causing serious disease in koalas. 

 While the detection of C. pecorum in several new marsupial hosts was interesting, perhaps the most surprising discovery was the detection of DNA sequences related to several recently described new chlamydia found in a survey of Australian ticks (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5267465/). Over the last 20 years or so, the access to DNA sequencing technology has revealed an untapped level of diversity of bacteria related to the ‘traditional’ chlamydial pathogens of koalas, humans and domesticated animals. Indeed, many of these new bacteria can be found in surprising locations, including amoeba and arthropods such as ticks, cockroaches and flies. The current study found that the most common chlamydial infections detected in non-koala marsupials were of tick origin, suggesting that, like several other bacterial pathogens, these novel chlamydiae may be transmitted by tick bite. Studies are now underway to investigate the disease-causing potential of these novel chlamydial infections of Australian marsupials. 

The work was funded by Australian Research Council Discovery (DP130102066) and Linkage Project (LP150100722) grants and a Holsworth Wildlife Endowment Grant and forms the major component of the PhD studies of USC student, Delaney Burnard. Please contact Assoc Prof Adam Polkinghorne, University of the Sunshine Coast (apolking@usc.edu.au) for further information.