A 5-year Chlamydia vaccination programme could reverse disease-related koala population decline: Predictions from a mathematical model using field data
Craig, AP, Hanger, J, Loader, J, Ellis, WAH, Callaghan, J, Dexter, C, Jones, D, Beagley, KW, Timms, P & Wilson, DP 2014, Vaccine, vol. 32, pp. 4163-4170.
Chlamydia vaccines are being developed to mitigate the impact the disease has on koala populations. Stochastic individual-based mathematical modelling suggests targeting female koalas aged 1-2 years old with a vaccine with 75% efficacy administered to approximately 10% of koalas per year could initiate a reversal in current population declines over a 5-6 year period.
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A guide for ecologists: detecting the role of disease in faunal declines and managing population recovery
Preece, ND, Abell, SE, Grogan, L, Wayne, A, Skerratt, LF, van Oosterzee, P, Shima, AL, Daszak, P, Field, H, Reiss, A, Berger, L, Rymer, TL, Fisher, DO, Lawes. MJ, Laurance, SG, McCallum, H, Esson, C, & Epstein, JH, 2017, Biological Conservation, vol. 214, pp. 136-146.
Disease can drive population declines in many ways such as lowering reproductive success, direct mortality and altering population structure, dispersal and migratory patterns. Its role in driving population decline, however, has received little attention. The authors of the current study argue that its role in species decline is more important than has previously been appreciated. A disease investigation framework consisting of ten steps was developed, with the help of scientists from multiple disciplines. This enabled investigators with diverse knowledge and experience in epidemiology to address disease as a potential factor in population declines.
The ten steps of disease determination were formulated based on knowledge and experience gained from three case studies of significant population crashes. These case studies included amphibian chytridiomycosis, Tasmanian devil facial tumour disease, and the effect of introduced predators on the wild population of Rufous Bettong. The ten steps of disease determination are: 1) identify and clearly define outcome of interest, 2) verify that decline is real by incorporating the best understanding of species’ ecology and demography, 3) determine spatial, temporal and demographic characteristics which can potentially reveal likely causes of decline, 4) list all plausible hypotheses of threatening processes, risk factors and causes, 5) Determine risk factors by considering the association between the outcome of interest and host and environmental factors, 6) undertake health and pathological examinations to identify whether pathogens are present, 7) formulate a tentative diagnosis, 8) implement management actions, 9) use multiple competing hypotheses approach to evaluate the relative influence of each hypothesis, and lastly, 10) refine ongoing management through monitoring and adapting to new information.
Most studies of mammalian population declines that happen across Australia did not recognise disease as a cause. In the Action Plan for Australian Mammals, disease is the putative cause in fewer than 20% of declining species.
Therefore, the development of this framework will ensure that disease as a source is acknowledged, and in turn will maximise the cost-effectiveness of diagnosis and management. Apart from considering the role of disease in population crashes, the authors also emphasize the importance of collaboration between different responsible parties. The various sources utilized included wildlife management, epidemiologists, ecologists, and veterinarians in determining the causes of population decline and planning of management strategies.
Summarised by Cherie Chan
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A multi-subunit chlamydial vaccine induces antibody and cell-mediated immunity in immunised koalas (Phascolarctos cinereus): comparison of three different adjuvants
Carey, AJ, Timms, P, Rawlinson, G, Brumm, J, Nilsson, K, Harris, JM & Beagley, KW 2009, American Journal of Reproductive Immunology, vol. 63, no. 1, pp. 161-172.
An experimental vaccine against Chlamydia induced Chlamydia-specific cell-mediated and antibody responses in immunised koalas. Of three different adjuvants tested, each in combination with a selection of recombinant chlamydial antigens, one caused adverse reactions in immunised koalas and was therefore considered unsafe and removed from the experiment. The remaining two adjuvants had no adverse effects, and both resulted in long-term (270 days) neutralising antibody responses in plasma against the three antigens as well as Chlamydia-specific peripheral blood mononuclear cell proliferative responses. In an artificial environment, plasma antibodies inhibited infections from two different species of Chlamydia, suggesting the approach trialled may be effective for combating chlamydial infections in koalas.
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