New strain of deadly Hendra virus discovered

The Australian veterinarian-led research project ‘Horses as Sentinels’ has identified a new strain of the deadly Hendra virus as the cause of a previously unexplained horse death in September 2015.

Hendra virus (HeV) is highly lethal in both horses and humans, with mortality rates approximately 79% and 60% respectively. The originally recognised strain of Hendra virus has resulted in the deaths of four humans and over 100 horses in Australia since it was first identified in 1994, when racehorse trainer Vic Rail and 13 racehorses in Hendra, Queensland, died after suffering a pneumonia-like illness.

The newly recognised variant has not been detected previously by routine biosecurity testing in horses; it was, however, detected in grey-headed flying fox samples from Adelaide in 2013 and found to share ~99% sequence identity with the 2015 horse case strain. Partial sequences of the variant have also been detected in flying foxes in other states.

Grey-headed flying foxes migrate and their range includes parts of southern Australia, which previous advice classed as low risk — with some interpreting this to mean negligible risk of Hendra virus spillover. Up until now, the original strain of Hendra virus has only been known to occur within the range of black flying foxes and spectacled flying foxes.

The findings indicate that HeV should be considered as a differential diagnosis in unvaccinated horses anywhere in Australia that flying foxes are present, and that unwell, suspect horses that return an initial negative Hendra virus test should continue to be treated with the same caution as a Hendra virus positive case, until testing for the new variant is performed.

The research team has developed updated diagnostic laboratory techniques capable of identifying the new strain, and will be sharing them with relevant laboratories. They have also established that the current Hendra virus horse vaccine is expected to be equally effective against the new strain.

On top of vaccination, there are a number of measures that people who work closely with horses can take to reduce the risk of infection with HeV and other viruses, including good biosecurity, use of personal protective equipment and good hygiene. It is also recommended that veterinarians, horse owners and handlers review their Hendra virus management plans.

Image credit: ©stock.adobe.com/au/vprotastchik

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