Abstracts Category : Other

Modelling transmission of Hendra virus from flying foxes to horses

by Muoz de Martn

Diseases that originate in wildlife and spillover to humans and domestic animals are of increasing public health concern. Of the wildlife groups in which emergent diseases originate, bats (Mammalia: Chyroptera) are a common source of some of the most virulent organisms: Ebola and Marburgh viruses, SARS Coronavirus and Nipah and Hendra viruses. Of these, Hendra virus (HeV, Paramyxoviridae: Henipavirus) is the only one that has not caused an epidemic outbreak a.er it spills over to horses and thence to humans. However, its geographic location in Australia represents an unparalleled opportunity to study spillover dynamics of emerging viruses, given the research capacity and human resources immediately available. .e importance of understanding spillover dynamics lies in the potential ability of reducing the risk of epidemics by decreasing the frequency of spillover. Since emergence HeV has spilled over to horses on 55 occasions along a 1500 km coastal stripe in eastern Australia, from northern Queensland to central New South Wales, with mortality rates in infected horses and humans close to 50-75%.In this study I used a series of modelling techniques to address basic questions of HeV epidemiology and ecology: What are the essential components of the spillover system? How is HeV transmitted from bats to horses? Which reservoir host species are more likely involved in spillover? What are the potential avenues to predict spillover occurrence? How does the spillover host affect spillover risk? How can we mitigate risk of HeV spillover?To identify the components of the HeV spillover system I participated in a workshop with the National HeV Research Program investigators. We discussed the available evidence and theory regarding spillover and published a conceptual model that is included here as Chapter 2. .e conceptual model consists of an explicit representation of the factors that have to be present for spillover to occur.Then, to find out how HeV is transmitted, I used unpublished experimental data on HeV survival at different temperatures in the laboratory (Australian Animal Health Laboratory, Paul Selleck), to generate a HeV survival model in the form of an ordinary differential equation. I used the model to test if survival could predict spillover in space (Chapter 3). .e poor predictive capacity of the HeV survival model suggested that transmission to horses could be direct. However, given that I could not completely rule out indirect transmission I quantified HeV decay in the microclimates it experiences once excreted in paddocks. With the simulations and analyses I found that HeV survival is lower on the ground than at ambient air temperatures, and that ground vegetation and tree shade increase survival. In addition, given that desiccation occurs in most circumstances and further decreases survival, HeV can seldom be indirectly transmitted (Chapter 4).At the time this project began in late 2012 it was not clear which of the four flying fox species were more important for spillover. To identify the most