Since 1994, Hendra has annually occurred in Queensland and more recently in New South Wales in horses and occasionally humans. To date, infections in humans have shown a 70% case mortality and although only 7 clinical cases have occurred, this poses a real threat to those that keep horses and those called in to treat potential Hendra cases. The causative virus has been shown to occur as a symptomless infection in fruit bats and that close contact between bats and horses leads to infection in horses. Once infected, horses become rapidly sick showing both respiratory and neurological signs and with death usual in 3 - 4 days. The infection in bats is poorly understood and whilst it is known that bats only intermittently shed virus, it is not known why this occurs or how the virus is transmitted from shedding bats to horses. Similarly, whilst it is clear from studies of the few clinical cases that very close contact is required between horses and humans for transmission to occur, the actual mode of transmission is unclear and the potential risk from infected horses exists even prior to the onset of clinical signs.
Underlying all control approaches has to be the application of basic biosecurity principles, reducing contact between bats and horses and introducing basic infection control procedures when dealing with potentially infected horses. Beyond this however, research has clearly identified the virus attachment protein allowing the development of a vaccine for use in horses, and the production of an immune sera for use in humans. Whilst these developments show real promise, further work is needed in understanding the infection process, undertaking safety studies with the immune sera and undertaking efficacy studies with the vaccine.