The deadly Hendra virus (Henipavirus) currently threatens a very restrained area of the world—specifically, the northeastern coastal regions of Australia in Queensland and northern New South Wales. But in the coming decades, that area could become less restrained, researchers say.
Where the virus will be located in the future depends on the locations of four relevant species: humans, horses, and two types of flying fox bats. And between now and, say, 2050, their location—and, thus, that of Hendra—could depend largely on climate change.
An international team of scientists says climate change could send Hendra-infected bats farther south and in contact with new local horse populations and humans in the southern coastal regions of Australia, as well as into the country’s inland territories.
“Adopting preventive measures at local scales will ultimately help cope with the increased risk to a larger horse population,” said Gerardo Martin, PhD, of the One Health Research Group at James Cook University College of Public Health, Medical, and Veterinary Sciences, in Townsville, Australia, and the Imperial College London Department of Infectious Disease Epidemiology, in the U.K.
While those local measures would help reduce risks to horses in areas where Hendra is present, broader initiatives could contribute to reducing the risk of Henipavirus spread itself, Martin said.
“At larger, probably national scales, measures to reduce greenhouse gas emissions could then slow down warming and the resulting shifting distributions of diseases such as Hendra and Ebola,” he said.
Hendra first appeared in 1994 near Brisbane, Australia, and has since killed nearly 100 horses and four humans. It can cause respiratory or neurologic problems in both species, but it doesn’t affect bats, which act as healthy reservoirs. Bats excrete the virus in their bodily fluids (mainly urine, but also fetal and birthing fluids), and horses pick up the virus by eating contaminated feed. Horses can then transmit the virus to other horses and humans through contact, although scientists still don’t fully understand the mode of transmission. It is still unknown whether humans can transmit it to other people or animals. So far none of the outbreaks in horses have resulted in epidemics, due to transmission being very limited, Martin said.
In their study, Martin and his fellow researchers, including scientists from the U.S. and Mexico, created statistical models to predict how Hendra virus could spread as the climate changes over the next 30 years. They took into consideration the specific kinds of bats that act as the main reservoirs of the virus—the black flying fox/fruit bat and spectacled flying fox/fruit bat—and studied their habitats and climate preferences.
They used advanced statistical modeling to predict that the number of horses at risk of Hendra infection could increase by 170% to 260% by 2050 due to climate change, he said. While this sounds alarming, their model actually shows a lower level of geographical expansion than other scientists have suggested. That’s because researchers originally thought four bat species transmitted the virus, but now it appears there’s only two. So Martin’s group focused only on the changing habitat of the black and spectacled flying foxes.
Regardless, the point of the study is not to alarm, Martin said. Rather, it’s to help horse owners prepare for the risks and carry out prevention tactics.
“I would say there are real reasons to be concerned about the potential consequences of climate change,” he said. People can offset these effects—which do remain theoretical at this stage, he added—through awareness and prevention strategies.
“Horse owners in and around areas at risk should undertake vaccination against Hendra virus,” he said. “Other measures likely to be effective to reduce exposure to the virus are keeping grass short under trees, reducing the foliage of trees so that there’s more light reaching the ground to reduce the viability of the virus urinated by bats, and fencing off fruiting and nectaring trees where bats feed, at least during the night.”
Those interested in the details of the model’s predictions and potentially affected areas can consult the scientific report online.
On a more general level, humans can contribute to reducing climate-change-related risks by modifying their habits.
“Based on the results of the model. I would recommend that people increase their efforts to reduce greenhouse gas emissions, so that the depicted scenarios in the models become less likely to take place,” Martin said.
It’s important to keep in mind, however, that this model is just that—a model—and isn’t necessarily what will happen in the future, Martin said.
“Models are only predictions, which are subject to an enormous amount of assumptions and, as we acknowledge, uncertainty,” he said. “To be certain of the predictions, we would have to continue observing and documenting how bat populations and Hendra virus levels change with climate change. We are just beginning to understand these bat-borne diseases and their interactions with climate, and this model only considers the effect of climate.
“On the one hand, it allowed us to identify very broad, coarse scale trends, but bats are complex organisms that are very much affected by other processes like land conversion and urbanization, which we did not take into account,” Martin continued. “I think we currently lack the capacity to say to what extent the predicted changes will occur.”
The study, “Climate Change Could Increase the Geographic Extent of Hendra Virus Spillover Risk,” was published in EcoHealth.