SPILLOVER PREVENTION
The development of a subunit vaccine containing recombinant HeV soluble G glycoprotein for horses was a major advance in managing HeV infection risk in horses. The additional benefit of potentially breaking the chain of transmission from flying-foxes to horses to humans has been proposed as an illustration of a One Health approach to the control of human disease (Middleton et al.
2014). Horses receiving an initial course of three doses, followed by annual boosters, have robust immune responses and demonstrate antibody levels consistent with protective immunity against infection (Middleton et al. 2014; Tan et al. 2018; Halpin et al. 2021). The uptake of the vaccine has been limited because of safety concerns expressed by some horse owners (Manyweathers et al. 2017), and some horse owners may request testing of antibody titres in their horse before booster vaccinations (Barrett et al. 2021).Experimental studies in unvaccinated horses showed that infected horses were increasingly infectious from the prodromal period, highlighting the need for appropriate- scaled PPE usage, risk assessment and case management for all equine consultations (Marsh et al. 2011). The limited available data on the duration of viral shedding from flying-foxes suggests that the duration of RNA shedding is short (Halpin et al. 2011) and viral loads in wild flyingfox populations are often low (Lunn et al. 2023). However, some flying-foxes excrete very high viral loads that are comparable to those seen in horses (Lunn et al. 2023), and so appropriate PPE is also warranted when handling flying-foxes (Wildlife Health Australia 2020).
Finally, the discovery of the protective effect of mass winter flowering presents an encouraging prospect for landscape-scale ecological interventions to prevent spillover (Eby et al. 2023). Improving the availability and reliability of critical flying-fox foraging habitat through restoration efforts would protect horses and people against spillover of Hendra and other viruses by restoring functioning ecosystems, improving the health of flying-foxes, and reducing their reliance on urban and agricultural areas (Eby et al. 2023). This is an example of how the extensive research on HeV spanning various disciplines continues to bridge critical knowledge gaps, facilitating more informed strategies for spillover risk mitigation and management and ongoing development of HeV as a model for the emergence, impact and investigation of other diseases at the wildlife-livestock-human interface.