The deadly Hendra virus is likely to extend its Australian range further south, modelling suggests, placing an additional 110,000 to 165,000 horses at risk.
Most cases of the bat-borne virus among horses are currently diagnosed in Queensland, with only rare cases in the northern regions of New South Wales. A spread south into New South Wales would expose many more horses to the risk of infection.
Hendra virus, first identified in 1994, is naturally carried by two of the four mainland Australian bat species, Pteropus alecto (the black flying fox) and Pteropus conspicillatuss (the spectacled flying fox).
The virus is capable of spilling over into horses, and then people, with a high fatality rate. Infected horses are routinely euthanized.
Researcher Gerardo Martin and his colleagues carried out disease risk mapping for the virus, producing two models to estimate areas at potential risk of Hendra spillover, based on climatic suitability for the two bat species that carry the virus.
They also included additional climatic variables that might affect spillover risk through other biological processes, such as bat or horse behaviour, plant cycles, and bat foraging habitat.
The study team, writing in the journal Ecohealth, said the modelling pointing to the southward expansion of the range of habitat suitable for the black flying fox, which has the potential to increase the number of horses at risk by 175% to 260%. This represented between 110,000 and 165,000 animals.
There was complete agreement among climate change scenarios on this range expansion, they said.
Changes to the northern tropical limits of the virus were highly uncertain because the modelling work indicated quite novel climatic conditions.
The study team found that the extent of areas at risk of spillover from the spectacled flying fox was predicted to shrink.
“Due to a likely expansion of P. alecto into these areas, it could replace P. conspicillatus as the main Hendra virus reservoir,” they suggested.
Some scenarios under the modelling also predicted that the black flying fox could expand its range inland.
The researchers, discussing their findings, say it is clear that direct intervention will be necessary to reduce risk in response to climate change, such as extending vaccine coverage regardless.
“However, a more holistic approach would include reduction of greenhouse gas emissions. Such a management strategy would positively impact all levels of organisation of the Hendra virus spillover system studied here and prevent other predicted consequences of climate change.
“For instance, the Australian tropics are predicted to experience large biodiversity losses and grasslands in southern Australia could experience increased variability in productivity which could affect the cattle and potentially the horse industry.”
The researchers recommend Hendra virus monitoring in bats and enhanced Hendra virus prevention in horses in areas predicted to be at risk. They propose that investigations be carried out to develop risk-reduction strategies for areas that could experience reservoir host replacements.
The full study team comprised Gerardo Martin, Carlos Yanez-Arenas, Carla Chen, Raina Plowright, Rebecca Webb, and Lee Skerratt.
Martin G, Yanez-Arenas C, Chen C, Plowright RK, Webb RJ, Skerratt LF. Climate Change Could Increase the Geographic Extent of Hendra Virus Spillover Risk. Ecohealth. 2018;15(3):509-525.