Hendra virus (HeV) is a paramyxovirus of the genus Henipavirus responsible for fatal infection in horses and humans in eastern Australia.
Flying-foxes of the genus Pteropus have been identified as reservoir hosts of the virus. The first recognised outbreak of a novel and highly lethal disease, which heralded the emergence of HeV, occurred 30 years ago (Black et al.
2015). Since then, much has been learnt about the virus, it’s devastating pathology in susceptible host species and its ecology in flying-foxes (Chiroptera, Pteropus spp.). An effective vaccine for horses became available in 2012 (Middleton et al.2014) and a post-exposure monoclonal antibody that has been available for compassionate use in humans since 2010 has successfully undergone human trials (Playford et al. 2020). Both the vaccine and monoclonal antibody appear effective against a novel Hendra variant (HeV genotype 2, HeV-g2) detected in flying-foxes since 2013 (Wang et al. 2021; Peel et al. 2022) and in horses in 2015 and 2021 (Annand et al. 2022; Taylor et al. 2022). This chapter covers updated knowledge from HeV research that has direct relevance to clinical and research wildlife veterinarians. With a continued global focus on bats as hosts of zoonotic viruses with pandemic potential, Hendra virus in Australian flying-foxes also remains a model system for understanding the processes driving virus emergence and ongoing spillover (Eby et al. 2023).
Hendra virus was first described following an outbreak in a horse racing stable in the Brisbane suburb of Hendra in 1994 (Murray et al. 1995a, 1995b; Selvey et al. 1995). Thirteen horses exhibited an acute respiratory syndrome and either died or were euthanased; a further seven horses were euthanased to eliminate ongoing risk (Murray et al. 1995a; Baldock et al. 1996). The trainer and a stablehand, succumbed to infection (the trainer fatally) following close contact with the initial equine cases, marking the first recorded fatal equine zoonosis (Selvey et al.
1995; McCormack et al. 1999). While no human cases have been reported since 2009, equine cases continue to be identified in Qld and NSW annually, totalling 67 HeV spillover events as of September 2023, involving 109 confirmed or suspected equine cases (Eby et al. 2022; Biosecurity Queensland 2023).Investigation of a wildlife origin of HeV had an early focus on flying-foxes because epidemiological features of the initial spillover events suggested a mobile mammalian host (Black et al. 2015). Neutralising antibodies to the virus were soon found in multiple flying-fox species (Halpin et al. 1996; Young et al. 1996; Field 2005) and the isolation of virus from free-ranging flying-fox foetal fluids and tissues supported flying-foxes as reservoir hosts (Halpin et al. 2000). Subsequent field-based investigations (Field et al. 2000, 2001, 2007; Field, 2005; Plowright et al. 2008, 2011; Breed et al. 2011, 2013) and experimental studies (Westbury et al. 1995, 1996; Williamson et al. 1998, 2000) provided key insights into HeV and its ecology, establishing a foundation for the research continuing to this day.
1.