Following its emergence in Queensland in 1994, Hendra virus (HeV) infection in horses has recurred on a regular basis with at least two disease events recognised in four of the past six years, and the 16 outbreaks to date in 2011 have already exceeded the total number identified over the past 15 years. Several outbreaks have extended to involve humans and the mortality rate in affected people is over 50%. The natural reservoir for HeV is the Australian flying-fox, with all four mainland species known to harbour the virus. However, infection of people has only been recognised following close contact with the secretions of diseased horses, especially at the time of terminal illness or during post mortem examination of horses that have died from HeV infection.

Reducing HeV exposure risk through the use of Personal Protective Equipment (PPE) during routine horse care has been heavily promoted, but there are inherent difficulties both in making reliable recommendations on this subject and relying on PPE for this purpose. However, immunisation of horses does hold promise both for providing protection against clinical illness in horses and also reducing viral shedding to a level that limits on-going transmission.

A subunit vaccine has been developed that is based on recombinantly expressed soluble versions of the HeV G glycoprotein (sG) and this is administered with adjuvant as an inactivated vaccine. Preliminary data demonstrate seroconversion of vaccinated horses and prevention of disease following exposure to an otherwise lethal HeV challenge. In addition, virus shedding was not detected in vaccinated horses and there was no evidence of virus replication in any tissue. Clearly, vaccination of horses against HeV has the potential both to protect the health of horses and to break the chain of transmission of HeV from bats to people.