Our team at the Wildlife Disease Association International Conference! Part 2 (oral presentations)

Members of our team recently attended (and presented at) the Wildlife Disease Association's 2015 International Conference.

Photos and oral presentation abstracts from our team can be found below (posters still to come):

Spillover: dynamics of cross-species transmission

Raina Plowright 1

1. Montana State University, Bozeman, MT, United States

Advances in genetic sequencing are now revealing the tremendous diversity of the microbial communities that inhabit or infect living organisms. However, it is difficult to identify the microbes that have the potential to spill over from other species to infect and cause disease in humans. We outline the ecological, epidemiological, and behavioral determinants of pathogen exposure and the within-host biological factors that shape susceptibility to spillover infections. By integrating the insights generated in currently isolated fields, we can quantify barriers to spillover, assess the risk of known pathogens to human health, and identify points of intervention and control.

Determining the role of fruit bat population dynamics in the emergence of Hendra virus in Australia

John R Giles 1, Peggy Eby 2, Alison J Peel 1, Raina K Plowright 3, Hamish McCallum 1

1. Environmental Futures Research Institute, South Brisbane, QLD, Australia

2. School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia

3. Department of Microbiology and Immunology, Montana State University, Bozeman, Montana, USA

Hendra virus (HeV) is a bat-borne RNA virus that has recently emerged as a human public health concern in Australia. HeV circulates in the large frugivorous and nectarivorous bats of the genus Pteropus (known colloquially as fruit bats or flying foxes). Periodically, spillover into an intermediate host (horses) occurs which amplifies viral populations before infecting humans. Anthropogenic influence and landscape change have been implicated as catalysts in the emergence of HeV, as well as analogous bat-borne diseases, such as Ebola and Nipah virus. Therefore, a quantitative understanding of the mechanisms that drive host population dynamics and pathogen epidemiology within the context of landscape change is an important and elusive requisite to predicting the behavior of a bat-borne disease system. Here, I present spatiotemporal models of both food resource distribution and foraging behavior of fruit bats, the combination of which enables a functional model of bat population dynamics at the landscape scale. My methods employ novel algorithms that analyze patterns in census counts at roosts of fruit bats across southeastern Queensland over the past decade, and mathematical models of social foraging behavior that characterize spatiotemporal flux of fruit bat populations over time. Some initial results indicate that large aggregations of bats are correlated with remotely sensed measures of eucalypt phenology, and the fission-fusion structure of bat populations appears to be driven by hyper-variable patterns of flowering and nectar production across the landscape. Robust prediction of the mechanistic interaction between food resource variability and bat population distribution facilitates parameterization of epidemiological models of viral transmission that are not vulnerable to typical confounders such as spatial population heterogeneity. And more broadly, it allows construction of scenarios that demonstrate how landscape change quantitatively influences bat population dynamics and ultimately drives spillover and emergence of bat-borne pathogens.

Modelling transmission dynamics of a novel Alphacoronavirus in an Australian population of large-footed myotis (Myotis macropus)

Jaewoon Jeong 1, Hamish McCallum 1, Alison J Peel 1, Craig S Smith 2, 3

1. School of Environment, Griffith University, Nathan, Qld, Australia

2. School of Veterinary Science, University of Queensland, Gatton, Queensland, Australia

3. Queensland Centre for Emerging Infectious Diseases, Biosecurity Queensland, Department of Agriculture and Fisheries, Coopers Plains, Queensland, Australia

Severe acute respiratory syndrome (SARS) emerged in 2002 to 2003 in southern China and Middle East respiratory syndrome (MERS) was detected in September 2012 in southwest Asia have underscored the potential of coronavirus to become emerging infectious diseases. Subsequently, the findings that the SARS coronavirus (SARS-CoV) and the MERS coronavirus (MERS-CoV) were originated from bats emphasized the importance of bats as reservoir hosts of emerging infectious diseases. Previously, mark-recapture data of a novel Australian bat Alphacoronavirus in Myotis macropus identified that this coronavirus was maintained in the population by persistent infected bats. We have taken one step further by utilizing more statistically intense methods of analyses in order to confirm the effects of persistent infection on the coronavirus maintenance in the population of bats. We additionally analysed the data by using ‘MARK’ and ‘OpenBUGS’ to estimate parameters, which subsequently were used to build compartment model, in which the effects of persistent infections against transient infection was estimated to see how it functions in maintenance of coronavirus. The mark-recapture analysis found no evidence that sex and age significantly affect the survival, recapture and transition rates between infection states. Infection was shown to make survival rate decreased slightly, and to make recapture rate increased. Modelling results suggested that the role of persistent infections is not quite dominant but certainly has an effect on the maintenance of coronavirus in the bat population. This study identifies potential effects of persistent infections in coronavirus transmission dynamics, and adds weight to the suggestion that these mechanisms may be an important coronavirus maintenance mechanism in bat populations, and, by extension, may be applicable to other bat RNA virus ecology.

Evolution of resistance to chytridiomycosis is associated with a robust early immune response in a wild amphibian

Laura F Grogan 1, 2, Scott D Cashins 2, Lee Berger 2, Lee F Skerratt 2, Michael S McFadden 3, Peter Harlow 3, David A Hunter 4, Benjamin C Scheele 5, Jason Mulvenna 6

1. Griffith University, Nathan, QLD, Australia

2. James Cook University, Townsville, QLD, Australia

3. Taronga Conservation Society, Mosman, NSW, Australia

4. NSW Office of Environment and Heritage, NSW State Government, Queanbeyan, NSW, Australia

5. Fenner School of Environment and Society, Australian National University, Canberra, ACT, Australia

6. Infectious Disease and Cancer, QIMR Berghofer Medical Research Institute, Herston, QLD, Australia

The fungus, Batrachochytrium dendrobatidis (Bd), aetiological agent of the devastating amphibian skin disease chytridiomycosis, is now considered endemic in most climatically suitable regions around the world. The evolution of or assisted selection for host immune resistance to chytridiomycosis may be a promising avenue for ensuring sustainable long-term persistence of Bd-threatened wild amphibians. For such a strategy to succeed it is essential to understand the mechanisms by which such resistance manifests. Here we examined transcriptomic responses of alpine tree frogs (Litoria verreauxii alpina) to subclinical Bd infection, comparing long-exposed populations to a naïve population. We performed a blinded, randomized and controlled exposure experiment, collecting skin, liver and spleen tissues at 4, 8 and 14 days post-exposure from 51 frogs for transcriptome assembly and differential gene expression analyses. We analysed our results in conjunction with data on infection intensities and the results of a large clinical survival experiment run concurrently in the same species. We identified a large number of significantly dysregulated transcripts (liver 1043, skin 8165, spleen 1665) in the tissues from subclinically infected individuals versus unexposed negative control frog tissue, including the predominant up-regulation of numerous transcripts associated with the host immune response (liver 132, skin 645, spleen 216). Our comparison between populations highlighted variations in response to subclinical infection associated with long-term population Bd exposure history and clinical evidence of survival. Individuals from the longest-surviving population demonstrated a larger complement of differentially expressed immune-associated genes in the skin at 4 days post exposure than frogs from the two more susceptible populations, consistent with a robust early innate and adaptive immune response. Our results support the concept of selecting for the evolution of resistance against chytridiomycosis, and suggest that an insufficient early immune response to infection may contribute to the susceptibility of this non-model species to chytridiomycosis.