Distribution of Hendra virus-carrying bats wider than once thought, findings suggest

Two Australian species of fruit bats previously considered low risk for the cross-species transmission of Hendra virus are carriers of a later variant of the pathogen.
A grey-headed flying fox. Photo: © Mike Lehmann, CC BY-SA 3.0 via Wikimedia Commons

Two Australian species of fruit bats previously considered low risk for the cross-species transmission of Hendra virus are carriers of a later variant of the pathogen, research has shown.

Hendra is a virus carried by bats that has caused lethal disease outbreaks in humans and horses in Australia.

Fruit bats, or flying foxes, are the wildlife reservoir from which the virus was first isolated in 1996.

Following the deaths of flying foxes in a 2013 heat wave, a new variant of the Hendra virus was discovered.

Jianning Wang and his fellow researchers, in a paper just published in the Virology Journal, have described the subsequent surveillance of Australian flying foxes for this novel virus over a nine-year period.

The study team, with the Australian Centre for Disease Preparedness, part of the science agency CSIRO, used molecular-based testing methods on samples taken from flying foxes submitted primarily for Australian bat lyssavirus diagnosis. Genome sequencing and characterisation of the novel Hendra variant was also undertaken.

Spleen and kidney samples harvested from the fox carcasses were initially screened with two real-time tests for the original Hendra virus. Two additional tests were developed specifically for the new strain, as reported earlier this week.

In the nine-year period, 98 flying foxes were tested and 11 were positive for the new variant. No samples were positive for the original Hendra virus.

Ten of the positive samples were from grey-headed flying foxes (Pteropus poliocephalus), although the authors noted that this species was over-represented in the opportunistic sampling (83% of the dead bats tested were this species).

The positive grey-headed flying fox samples were collected from Victoria and South Australia and one positive little red flying fox (Pteropus scapulatus) was collected from Western Australia.

Genetic sequencing shows the new variant belongs to the Hendra species but occupies a distinct lineage, they reported. They designated it Hendra Virus genotype 2.

The identification and characterisation of a new variant, in two species of flying fox previously deemed to be low risk for cross-species transmission, in regions where spill-over has not occurred, is a significant contribution to Hendra epidemiology in Australia, they said.

The recent retrospective identification of a virus belonging to this sub-lineage from a 2015 case of equine neurological disease in Queensland shows the new variant is able to infect horses and potentially cause disease.

Further studies on its disease-causing abilities and the risk of spill-over events are warranted, the study team said.

The new variant causes vasculitis in the flying fox host, the authors reported.

Due to high levels of genome similarity with the original lineage, the new variant can be considered a zoonotic pathogen, posing a significant risk to different species of animals, particularly horses and humans, they said.

The development of the new tests reported in this study will significantly improve the detection, diagnosis and surveillance of the new variant in flying foxes and other host species, they wrote.

Wang, J., Anderson, D.E., Halpin, K. et al. A new Hendra virus genotype found in Australian flying foxes. Virol J 18, 197 (2021). https://doi.org/10.1186/s12985-021-01652-7

The study, published under a Creative Commons License, can be read here




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