Special Issue "Health and Diseases of Koalas"

A special issue of Animals (ISSN 2076-2615). This special issue belongs to the section "Wildlife".

Deadline for manuscript submissions: 31 October 2021.

Special Issue Editor

Dr. Natasha Speight
E-Mail Website
Guest Editor
School of Animal and Veterinary Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
Interests: koalas; oxalate nephrosis; chlamydiosis; koala retrovirus; mange; disease

Special Issue Information

Dear Colleagues,

Koala populations are declining across Australia, and a major threat to them is disease. Chlamydia and koala retrovirus are two key infectious pathogens of koalas, which cause ocular and urogenital disease, and leukemic and lymphomic cancers, respectively. Research has uncovered many complex mechanisms in the pathogenesis of both these infections, and the potential for koala retrovirus to predispose to chlamydial disease. Other infectious conditions of koalas include the virus Phascolarctid herpesvirus, and the parasitic infection Sarcoptes scabiei, whilst non-infectious diseases include oxalate nephrosis, a renal disease associated with a build-up of calcium oxalate crystals in the kidney. Together with the threats of climate change effects such as drought and bushfires, it is important to understand how koalas are affected by disease based on their unique physiological adaptations as a eucalypt specialist.

Novel papers from different aspects of koala health and disease are invited to this Special Issue that aims to bring together the latest research on koalas, such as (but not limited to):

  • Unravelling the complexity of infectious diseases of koalas;
  • Pathological conditions of koalas;
  • Climate-change-related health and dietary issues;
  • Role of gut microbiota in koala health.

Dr. Natasha Speight
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Animals is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

  • koalas
  • health
  • disease
  • Chlamydiosis
  • koala retrovirus
  • gut microbiome
  • pathology

Published Papers (4 papers)

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Research

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Article
Seasonal Variations of Faecal Cortisol Metabolites in Koalas in South East Queensland
Animals 2021, 11(6), 1622; https://doi.org/10.3390/ani11061622 - 31 May 2021
Cited by 1 | Viewed by 953
Abstract
The Koala (Phascolarctos cinereus) is an endemic marsupial inhabiting four states of Australia. Urbanisation, declining habitat, drought and fires are threatening the survival of this flagship species. These threats may cause acute and chronic stress in koalas, which might also be [...] Read more.
The Koala (Phascolarctos cinereus) is an endemic marsupial inhabiting four states of Australia. Urbanisation, declining habitat, drought and fires are threatening the survival of this flagship species. These threats may cause acute and chronic stress in koalas, which might also be associated with occurrence of infectious diseases in koala populations. Stress may induce an increase in cortisol reflected in increased faecal cortisol metabolite (FCM) values. To be able to use faecal cortisol metabolites to measure stress levels in this species, our aim was to determine baseline values for males and females during breeding and non-breeding season. A total of 351 defecations were collected fortnightly, twice a day, for 12 months from koalas at a wildlife facility in South East Queensland. Samples were analysed with three different enzyme immunoassays (EIAs): a cortisol, 5α-pregnane-3β,11β,21-triol-20-one (37e) and tetrahydrocorticosterone (50c) EIA. The latter, which also reacts with tetrahydrocortisol, the main metabolite in koala faeces, was found to have the highest biological sensitivity and, therefore, is the most suitable EIA to measure stress levels in koalas. Utilising this EIA, we found significant differences (p < 0.05) in FCM values between males and females, breeding and non-breeding season, and between morning and evening samples. Values of faecal cortisol metabolites established in stress-free koalas in this study can serve as a reference for future studies in koalas. Full article
(This article belongs to the Special Issue Health and Diseases of Koalas)
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Article
Molecular Diagnosis of Koala Retrovirus (KoRV) in South Australian Koalas (Phascolarctos cinereus)
Animals 2021, 11(5), 1477; https://doi.org/10.3390/ani11051477 - 20 May 2021
Viewed by 979
Abstract
Koala retrovirus, a recent discovery in Australian koalas, is endogenised in 100% of northern koalas but has lower prevalence in southern populations, with lower proviral and viral loads, and an undetermined level of endogenisation. KoRV has been associated with lymphoid neoplasia, e.g., lymphoma. [...] Read more.
Koala retrovirus, a recent discovery in Australian koalas, is endogenised in 100% of northern koalas but has lower prevalence in southern populations, with lower proviral and viral loads, and an undetermined level of endogenisation. KoRV has been associated with lymphoid neoplasia, e.g., lymphoma. Recent studies have revealed high complexity in southern koala retroviral infections, with a need to clarify what constitutes positive and negative cases. This study aimed to define KoRV infection status in Mount Lofty Ranges koalas in South Australia using RNA-seq and proviral analysis (n = 216). The basis for positivity of KoRV was deemed the presence of central regions of the KoRV genome (gag 2, pol, env 1, and env 2) and based on this, 41% (89/216) koalas were positive, 57% (124/216) negative, and 2% inconclusive. These genes showed higher expression in lymph node tissue from KoRV positive koalas with lymphoma compared with other KoRV positive koalas, which showed lower, fragmented expression. Terminal regions (LTRs, partial gag, and partial env) were present in SA koalas regardless of KoRV status, with almost all (99.5%, 215/216) koalas positive for gag 1 by proviral PCR. Further investigation is needed to understand the differences in KoRV infection in southern koala populations. Full article
(This article belongs to the Special Issue Health and Diseases of Koalas)
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Article
Toll-Like Receptor Expression Profiles in Koala (Phascolarctos cinereus) Peripheral Blood Mononuclear Cells Infected with Multiple KoRV Subtypes
Animals 2021, 11(4), 983; https://doi.org/10.3390/ani11040983 - 01 Apr 2021
Cited by 1 | Viewed by 727
Abstract
Toll-like receptors (TLRs), evolutionarily conserved pattern recognition receptors, play an important role in innate immunity by recognizing microbial pathogen-associated molecular patterns. Koala retrovirus (KoRV), a major koala pathogen, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-B to J). However, the expression profile [...] Read more.
Toll-like receptors (TLRs), evolutionarily conserved pattern recognition receptors, play an important role in innate immunity by recognizing microbial pathogen-associated molecular patterns. Koala retrovirus (KoRV), a major koala pathogen, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-B to J). However, the expression profile of TLRs in koalas infected with KoRV-A and other subtypes is yet to characterize. Here, we investigated TLR expression profiles in koalas with a range of subtype infection profiles (KoRV-A only vs. KoRV-A with KoRV-B and/or -C). To this end, we cloned partial sequences for TLRs (TLR2–10 and TLR13), developed real-time PCR assays, and determined TLRs mRNA expression patterns in koala PBMCs and/or tissues. All the reported TLRs for koala were expressed in PBMCs, and variations in TLR expression were observed in koalas infected with exogenous subtypes (KoRV-B and KoRV-C) compared to the endogenous subtype (KoRV-A) only, which indicates the implications of TLRs in KoRV infection. TLRs were also found to be differentially expressed in koala tissues. This is the first report of TLR expression profiles in koala, which provides insights into koala’s immune response to KoRV infection that could be utilized for the future exploitation of TLR modulators in the maintenance of koala health. Full article
(This article belongs to the Special Issue Health and Diseases of Koalas)
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Review

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Review
The Koala Immune Response to Chlamydial Infection and Vaccine Development—Advancing Our Immunological Understanding
Animals 2021, 11(2), 380; https://doi.org/10.3390/ani11020380 - 03 Feb 2021
Viewed by 950
Abstract
Chlamydia is a significant pathogen for many species, including the much-loved Australian marsupial, the koala (Phascolarctos cinereus). To combat this situation, focused research has gone into the development and refinement of a chlamydial vaccine for koalas. The foundation of this process [...] Read more.
Chlamydia is a significant pathogen for many species, including the much-loved Australian marsupial, the koala (Phascolarctos cinereus). To combat this situation, focused research has gone into the development and refinement of a chlamydial vaccine for koalas. The foundation of this process has involved characterising the immune response of koalas to both natural chlamydial infection as well as vaccination. From parallels in human and mouse research, it is well-established that an effective anti-chlamydial response will involve a balance of cell-mediated Th1 responses involving interferon-gamma (IFN-γ), humoral Th2 responses involving systemic IgG and mucosal IgA, and inflammatory Th17 responses involving interleukin 17 (IL-17) and neutrophils. Characterisation of koalas with chlamydial disease has shown increased expression within all three of these major immunological pathways and monitoring of koalas’ post-vaccination has detected further enhancements to these key pathways. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off. Recent advances in marsupial genetic knowledge and general nucleic acid assay technology have moved koala immunological research a step closer to other mammalian research systems. However, koala-specific reagents to directly assay cytokine levels and cell-surface markers are still needed to progress our understanding of koala immunology. Full article
(This article belongs to the Special Issue Health and Diseases of Koalas)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: The koala immune response to chlamydial infection and vaccine development – advancing our immunological understanding
Authors: Bonnie L Quigley; Peter Timms
Affiliation: University of the Sunshine Coast, Sippy Downs, Australia
Abstract: Chlamydia is a significant pathogen for many species, including the much-loved Australian marsupial, the koala (Phascolarctos cinereus). To combat this situation, focused research has gone into the development and refinement of a chlamydial vaccine for koalas. The foundation of this process has involved characterizing the immune response of koalas to both natural chlamydial infection as well as vaccination. From parallels in human and mouse research, it is well-established that an effective anti-chlamydial response will involve a balance of cell-mediated Th1 responses involving interferon-gamma (IFN-γ), humoral Th2 responses involving systemic IgG and mucosal IgA, and inflammatory Th17 responses involving interleukin 17 (IL-17) and neutrophils. Characterization of koalas with chlamydial disease has shown increased expression within all three of these major immunological pathways and monitoring of koalas’ post-vaccination has detected further enhancements to these key pathways. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off. Recent advances in marsupial genetic knowledge and general nucleic acid assay technology has moved koala immunological research a step closer to other mammalian research systems. However, koala-specific reagents to directly assay cytokine levels and cell-surface markers are still needed to progress our understanding of koala immunology.

title: Pilot study of physiological stress evaluation in rescued wild koalas in a rehabilitation sanctuary
Authors: Edward Narayan, Renae Charalambous, Troy Simonato
Author Affiliations: School of Agriculture and Food Sciences, The University of Queensland, Australia School of Science, Western Sydney University, Australia
Abstract: Koalas (Phascolarctos cinereus) is one of Australia's highly charismatic native small marsupial species however it also continues to face increasing pressure from environmental trauma and diseases. Negative stimulants in the environment can elicit stress responses through activation of the hypothalamic-pituitary-adrenal (HPA) axis. This response can be either acute or chronic and is shown through the activation of the neuroendocrine stress system and the release of glucocorticoids (e.g. cortisol). Wild koalas entering care also face novel physical and psychological stressors that can be out of a wildlife carer's control. In this pilot study, we monitored physiological stress in three newly arrived wild koalas over a period of seven months at a wildlife rehabilitation centre in NSW, Australia. Physiological stress was indexed non-invasively using fecal glucocorticoid metabolites (FCM) analysis. The koalas were rescued due mainly due to trauma incurred from vehicle collision and health issues such as blindness and cryptosporidium infection and were unreleasable back to the wild. The results show the changes in fecal cortisol metabolite levels of the three koalas in relation to specific environmental factors such as construction noise, storms, interactions with other koalas, and public presence. To our knowledge, this is the first evidence of stress tracking of wild rescued koalas in a sanctuary. Further monitoring will be needed to better understand how koalas respond to external cues and whether they can be successfully adapted long-term into the sanctuary.

title: Seasonal variations of faecal glucocorticoid metabolites in koalas in South-East Queensland
Authors: Flavia Santamaria 1*, Rupert Palme 2*, Rolf Schlagloth 1, Edith Klobetz-Rassam 2 and Joerg Henning 3
Author Affiliations: 1 School of Health, Medical and Applied Sciences, Central Queensland University; 2 Department of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria; 3 School of Veterinary Science, University of Queensland.
Abstract: The Koala (Phascolarctos cinereus) is an endemic marsupial inhabiting eastern Australia. Koalas are listed as vulnerable in Queensland. Urbanisation, other anthropogenic activities and drought caused by climate change are threats to the survival of this flagship species. Rural koala populations are also increasingly impacted. These threats may cause acute and chronic stress which may induce an increase in glucocorticoids reflected in increased faecal glucocorticoid metabolite values. To be able to use faecal cortisol metabolites to establish a link between these threats and adrenocortical activity, our aim was to determine baseline values for male and female koalas during mating and non-mating season. We hypothesised that, during the mating season, average values would be higher for both sexes. A total of 355 defecations were collected fortnightly for 12 months (morning and afternoon) from five females and four males at a wildlife facility in South-East Queensland. Based on the results of our previous study on the characterisation of faecal glucocorticoid metabolite in koalas (article in preparation) samples were analysed with three different enzyme immunoassays. We showed a significant difference between faecal glucocorticoid metabolite values for both sexes during the mating season. These values serve as a reference for future faecal cortisol metabolite studies in koalas.

Vaccination against the Koala Retrovirus (KoRV): Problems and strategies

Joachim Denner

Anti-chlamydial therapy of the male koala reproductive system and its role in genetic rescue

Lyndal Hulse

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