Hendra virus (HeV) belongs to the genus Henipavirus (family Paramyxoviridae), and is an emerging zoonotic virus. The virus is transmitted to humans via an intermediary equine host from bats of the genus Pteropus, colloquially referred to as flying foxes. HeV was first identified in 1994 following an outbreak in Hendra, a suburb of Brisbane, Queensland, Australia that resulted in the infection of 20 horses and two humans. There have been 31 identified spillovers of Hendra virus, resulting in a total 66 attributed equine cases and 7 human cases resulting in 4 human deaths. In an unprecedented year for HeV activity, 17 spillovers resulting in 21 infections in horses have been identified between June and August 2011. The first infection in a dog was also diagnosed. Due to its wide host range, high mortality and lack of effective prevention or treatment modalities, HeV is classified in the highest biological safety category – BSL4.
Multiple genetic variants of HeV circulating at one time were observed previously in July 2008 when there were two concurrent outbreaks in horses over 930 km apart. Spillovers of HeV from flying foxes into horses are most likely due to the increased incidence of horses coming into contact with excretions from flying foxes when compared to humans. In addition, horses may be more susceptible to HeV infection as their innate immune response genes are genetically most closely related to flying foxes. Intimate contact between horses and humans have been found to be required for infection, however, no direct transmission from bats to humans has been detected. The possibility of direct HeV infection from bats to humans cannot be ruled out. When spillovers occur from horses to humans the variation observed in HeV variants is minimal.
Identifying Hendra Virus Diversity in Pteropid Bats. (2011) PLoS ONE 6(9): e25275. doi:10.1371/journal.pone.0025275
Hendra virus (HeV) causes a zoonotic disease with high mortality that is transmitted to humans from bats of the genus Pteropus (flying foxes) via an intermediary equine host. Factors promoting spillover from bats to horses are uncertain at this time, but plausibly encompass host and/or agent and/or environmental factors. There is a lack of HeV sequence information derived from the natural bat host, as previously sequences have only been obtained from horses or humans following spillover events. In order to obtain an insight into possible variants of HeV circulating in flying foxes, collection of urine was undertaken in multiple flying fox roosts in Queensland, Australia. HeV was found to be geographically widespread in flying foxes with a number of HeV variants circulating at the one time at multiple locations, while at times the same variant was found circulating at disparate locations. Sequence diversity within variants allowed differentiation on the basis of nucleotide changes, and hypervariable regions in the genome were identified that could be used to differentiate circulating variants. Further, during the study, HeV was isolated from the urine of flying foxes on four occasions from three different locations. The data indicates that spillover events do not correlate with particular HeV isolates, suggesting that host and/or environmental factors are the primary determinants of bat-horse spillover. Thus future spillover events are likely to occur, and there is an on-going need for effective risk management strategies for both human and animal health.