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The ecology and epidemiology of devil facial tumour disease
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Abstract
Emerging infectious diseases are increasingly recognised as a significant threatening
process in conservation biology. Empirical studies aimed at understanding the
epidemiological and ecological processes underlying disease transmission and its
impact on host populations are crucial for designing disease management strategies.
The Tasmanian devil (Sarcophilus harrisii), is threatened with extinction by Devil
Facial Tumour Disease (DFTD), a novel and fatal transmissible cancer. In this thesis,
I use proximity-sensing radio collars to reveal empirical contact networks in a wild
devil population and infer the role of seasonal and demographic network structure
dynamics in the epidemiology of DFTD. I further use this information to build
disease-simulation network models to assess the role of contact heterogeneities in
epidemic behaviour. Finally, I use longitudinal data sets that followed the natural
progression of DFTD to compare contact patterns, epidemiology and impact of the
disease in subpopulations which differ in their genotypic structure and diversity.
The results indicate increased frequency and length of male-female contacts during
the mating season, compared with the non-mating season. These strong inter-sex
contact preferences during the mating season suggest that the transmission dynamics
of DFTD might be frequency dependent. There are strongly connected individuals in
the network, but their identity changes with season, providing limited scope for
targeting disease control actions to particular demographic groups.
Incorporating network structure and its seasonal and demographic dynamics in
disease simulation models had a modest effect on the epidemic threshold for DFTD
compared to traditional compartmental disease models. Quantifying heterogeneities in
contact patterns and assessing their role in disease spread do, nonetheless, represent
an important step for predicting epidemic behaviour and developing approaches for
managing wildlife diseases.
This study has provided the first evidence of reduced impact and slow progression of
DFTD in a wild population as the disease moves to a genetic subpopulation with
major histocompatibility complex genes differing from those of the tumour itself.
Biting patterns associated with disease transmission did not significantly differ
between the two genetic subpopulations. Therefore, differences in genetic diversity in
the host immune system or reduced virulence in the pathogen are proposed as
plausible explanations for the epidemiological differences between subpopulations. In
addition, I found that most tumours were located inside the oral cavity and devils with
fewer bites were more likely to develop DFTD, which suggests that the probability of
acquiring infection is higher in devils delivering bites than in those receiving bites.
The findings of this study, which examined the natural progression of an emerging
disease in an ecological and epidemiological context, have direct implications for
designing future conservation strategies for the species, and are broadly applicable to
a range of other conservation challenges posed by wildlife diseases.
| Item Type: | Thesis - PhD |
|---|---|
| Authors/Creators: | Hamede, RK |
| Keywords: | Tasmanian devil facial tumour disease, wildlife disease ecology, social networks, contact rates, epidemiology, infectious cancer, disease transmission, social behaviour, seasonality, biting patterns, disease management |
| Copyright Information: | Copyright 2012 the Author |
| Additional Information: | Chapter 2 appears to be the equivalent of the peer reviewed version of the following article: Hamede, R., Bashford, J., McCallum, H. and Jones, M., 2009, Contact networks in a wild Tasmanian devil (Sarcophilus harrisii) population: using social network Chapter 3 appears to be the equivalent of the peer reviewed version of the following article: Hamede, R., Bashford, J., Jones, M and McCallum, H., 2012, Simulating devil facial tumour disease outbreaks across empirically derived contact networks. Journal of applied ecology, 49(2), 447-456, which has been published in final form at 10.1111/j.1365-2664.2011.02103.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Chapter 4 appears to be the equivalent of the peer reviewed version of the following article: Hamede, R., Lachish, S., Belov, K., Woods, G., Kreiss, A., Pearse, A.M., Lazenby, B., Jones, M. & McCallum, H., 2012, Reduced effect of Tasmanian devil facial tumour Chapter 5 appears to be the equivalent of the peer reviewed version of the following article: Hamede, R., McCallum, H., Jones, M., 2013, Biting injuries and transmission of Tasmanian devil facial tumour disease. Journal of animal ecology, 82(1), 182-190, which has been published in final form at 10.1111/j.1365-2656.2012.02025.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Appendices 1 and 2 have been removed but links to the published articles at the publishers' websites are included in this record. Appendix 3 is a published paper: McCallum, H., Jones, M., Hawkins, C., Hamede, R., Lachish, S., Sinn, D. L., Beeton, N. and Lazenby, B., 2009, Transmission dynamics of Tasmanian devil facial tumor disease may lead to disease-induced extinction. Ecology, 90(12), 3379–3392. doi:10.1890/08-1763.1 |
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