Researchers have completed the analysis of the new Hendra virus variant which was detected by routine testing from a horse who died in 2015 but had tested negative to HeV infection.

They say that the current vaccine will be effective against the new strain, now named Hendra virus Genotype 2 (HeV-g2).

The results of the study led by the ‘Horses as Sentinels’ research team, are published in the journal Emerging Infectious Diseases.

CSIRO and the ‘Horses as Sentinels’ project team have been working closely with vets and laboratories around Australia to implement improved tests for horses with signs of Hendra virus disease. The tests can detect and differentiate both types of Hendra virus with a high degree of accuracy.

Genome-sequencing and detailed analysis of the new strain’s features have found that its receptor-binding protein shares sufficient similarities with the previously known virus for the researchers to confidently state that the current human monoclonal antibody treatment and equine vaccine will be effective against this new variant.

These advanced genetic-testing technologies can avoid the need to conduct challenge trials on horses, something that scientists aim to avoid due to the significant welfare impact.

Keeping an eye on emerging diseases

‘Horses as Sentinels’ is an Australian veterinarian-led research project that aims to identify previously unknown viruses that cannot be detected by the current diagnostic tests. Once a new strain or virus is identified, new tests can be developed.

The project was founded by Dr Peter Reid, the veterinarian who helped identify the virus when he attended, in 1994, the 24 horses who died during the first outbreak in the suburb of Hendra, Brisbane. Since then, 4 people and over 100 horses have died after contracting the disease.

The research, which is funded by a Biosecurity Innovation Program grant from the Department of Agriculture, Water and the Environment, found HeV-g2 present in samples collected from one horse from Queensland, in 2015. The horse presented with severe disease signs consistent with Hendra virus infection but had tested negative to the known HeV strain.

In October 2021, the new genetic type was also detected in a horse near Newcastle in New South Wales, the most southern case of Hendra yet recorded.

All Australian horse owners and vets should remain vigilant

The findings show there is a greater diversity of HeV strains than was previously recognised circulating among flying fox species in Australia, meaning Hendra can be found across a broader region of Australia than previously thought.

HeV should be considered as a differential diagnosis in unvaccinated horses anywhere in Australia that flying foxes are present, and unwell, suspect horses which 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 newly recognised variant found in the Queensland horse who died in 2015 and the NSW horse who died in 2021, is 99 percent identical to the virus detected as present in grey-headed flying fox samples from Adelaide, South Australia, in 2013. The previously known strain is linked to the black flying fox that lives in northern Australia.

Biosecurity measures

These findings are a reminder of measures that horse owners and people who work closely with horses can put in place to reduce the risk of infection.

Biosecurity measures, such as vaccination of horses for Hendra virus and seeking veterinary attention for sick horses will help to minimise the risk of disease transmission.

To help prevent Hendra virus in horses, reduce the opportunity for flying-foxes and horses to interact. Do this by removing feed bins and water troughs from under or near trees. Remove horses or restrict their access to paddocks where flowering or fruiting trees attract flying-foxes.

Flying foxes are protected animals, with two species on our nationally vulnerable list. They are critical to our environment because they pollinate our native trees and plants and also spread their seeds.

Without flying foxes, we wouldn’t have our eucalypt forests, rainforests and melaleucas.

The study is open access and can be found here.

Further reading:

Hendra virus disease fact sheet