The National Hendra virus Research Program (NHeVRP) symposium was held in Brisbane on 1-2 June, 2016, bringing together researchers funded under this $12 million program as well as stakeholders from the equine, veterinary, medical, and policy arenas. Professor Hamish McCallum was unable to attend in person, but presented via pre-recorded video on the outcomes of three years the research led by himself and Assistant Professor Raina Plowright (Bozeman Disease Ecology Lab): “Models to predict Hendra virus prevalence in flying fox populations”. Dr. Alison Peel represented Hamish and Raina on the question and answer panel following that session in their absence.
Our study is developing models that will enable prediction of flying fox colony dynamics, patterns of high prevalence and intensity of Hendra virus infection in such colonies, and the subsequent risk of transmission of Hendra virus to horses. Hamish’s presentation covered various conceptual advances from the study, including:
a conceptual model that breaks down cross-species spillover processes into various necessary layers, from within-host processes that drive virus excretion to land-use changes that increase interaction among species (Plowright et al. 2015).
a synthetic framework for animal-to-human transmission that integrates the many processes involved and allows quantitative modelling (Plowright et al., in review).
a paper exploring hypotheses that may explain temporal and spatial pulses of virus shedding in bat populations (episodic shedding from persistently infected bats or transient epidemics that occur as virus is transmitted among bat populations), and a suggested research agenda that would allow differentiation between these scenarios (Plowright et al, PLoS Neglected Tropical Diseases, in press)
Hamish also described a spatial model of flying fox colony dynamics developed by John Giles, which is able to predict flying fox presence and abundance through climate and remote sensing vegetation data (Giles et al, in review), and time-series analysis of HeV virus prevalence data which aims to further investigate periodicity of HeV dynamics and its drivers (Paez et al, in preparation).
Clear outcomes from other presentations at the meeting include that the equine horse vaccine remains the single most effective preventative measure against Hendra infection in horses, and subsequently in humans. Findings from the QLD and NSW governments (Field et al 2015, Smith et al, Edson et al, Goldspink et al) indicate that black and spectacled flying foxes are the main carriers of HeV, and subsequently that horses pastured within the distribution of these two species are at greater risk for HeV spillover, and are strongest candidates for vaccination.
Additionally, research out of the CSIRO Australian Animal Health Laboratory (AAHL), Geelong suggests that while HeV RNA may be persistently maintained within the brain of previously infected animals and humans, and this has rarely resulted in return of disease after a long period, there is no evidence to suggest that these individuals are able to excrete infectious virus particles and contribute to transmission.
Risk management strategies were reiterated and refined over the course of the RIRDC-funded research program and effective communication of recommended practices to horse owners is fundamental. This was highlighted by Melanie Taylor’s research, which used online surveys and in-depth interviews to gain an understanding of risk perception among horse owners, their engagement and factors influencing their uptake of recommended practices (including the HeV vaccine). This research identified ‘an urgent need to protect and preserve the veterinarian-horse owner relationship, through encouraging an open and collaborative approach to decision-making to mitigate the risk of Hendra virus’.
Valuable representation at the symposium from the equine industry highlighted the challenges still faced in regulating vaccine use for events, the financial considerations of vaccinating large numbers of horses, and the potential effect of the vaccine on race horse performance.
Finally, Peter Reid, the equine veterinarian present at the first HeV outbreak in 1994, gave a personal and engaging account of his experiences, and how Hendra virus research has developed over the years.
A compendium of the findings from all groups funded by the National Hendra Virus Research Program is now available online (rirdc.infoservices.com.au/items/16-001).