To prevent new viruses from spreading to humans, we need to protect and restore bat habitats

To prevent new viruses from spreading to humans, we need to protect and restore bat habitats

Grey-headed flying foxes prefer to roost in large groups and feed on eucalyptus nectar. But when there are no eucalyptus trees, they forage in rural and suburban areas. Credit: Vivien Jones, author provided

Bats have lived with coronaviruses for millennia. Details are still unclear about how one of these viruses evolved into SARS-CoV-2, which causes COVID in humans. Did it go directly from bats to humans or via another species? When? And why? If we can’t answer these questions for this now infamous virus, we have little hope of preventing the next pandemic.

Some bat species are hosts to other viruses deadly to humans, from rabies to Nipah to Hendra. But their super-powered immune system allows them to coexist with these viruses without looking sick.

So what can we do to prevent these viruses from popping up in the first place? We found a surprisingly simple answer in our new research on flying foxes in Australia: protect and restore native bat habitats to increase natural protection.

When we destroy native forests, we force nectar-eating flying foxes into survival mode. They are shifting from primarily nomadic animals that follow eucalyptus blooms and form large roosts to less mobile animals that live in a large number of small roosts near farmland where they may interact with horses.

The Hendra virus is transmitted by bats and can spread to horses. It doesn’t often spread from horses to humans, but when it does, it’s extremely dangerous. Two thirds of Hendra cases in horses have occurred in heavily cleared areas of northern New South Wales and southeastern Queensland. That’s no coincidence.

Now that we know how habitat destruction and overflow are linked, we can take action. Protecting the eucalyptus species that flying foxes rely on reduces the risk of the virus spreading to horses and then to humans. The data we’ve collected also makes it possible to predict times of increased Hendra virus risk – up to two years in advance.

What have we discovered?

Many Australians love flying foxes. Our largest flying mammal is often seen framed against the summer night sky in cities.

These nectar-loving bats play a vital ecosystem role in pollinating Australia’s native trees. (Pollination in Australia isn’t limited to bees – flies, moths, birds and bats do too). In winter they depend on nectar from a few tree species, such as red bush gum (Eucalyptus tereticornis) which is mainly found in southeastern Queensland and northeastern NSW. Unfortunately, most of this habitat has been cleared for agriculture or cities.

Flying foxes are typically nomadic and fly great distances across the landscape. When eucalypts come into bloom in certain areas, these bats will descend on the abundant food and congregate in vibrant nests, often more than 100,000 strong.

But Australia is a tough country. During the severe drought caused by El Niño, eucalyptus trees may stop producing nectar. To survive, flying foxes must change their behavior. Gone are the big sleeping places. Instead, bats scattered in many directions, seeking other food sources, such as introduced fruit. This reaction usually only lasts a few weeks. When the eucalyptus blooms resume, the bats come back to feed in native forests again.

But what happens when there aren’t enough forests to return to?

Between 1996 and 2020, we found that large winter roosts of nomadic bats in south-east Queensland were becoming increasingly rare. Instead, flying foxes formed small roosts in rural areas that they would normally have ignored and fed on introduced plants such as privet, camphor laurel and citrus fruits. This has brought them closer contact with horses.

In related research published last month, we found that the smaller nests formed in these rural areas also had higher detection rates of Hendra virus, especially in winter after a climate-induced nectar shortage.

To prevent new viruses from spreading to humans, we need to protect and restore bat habitats

Flying foxes are social, intelligent and play a key role in pollinating native trees. Credit: Vivien Jones, author provided

An early warning system for the Hendra virus

Our models confirmed that strong El Niño events caused nectar shortages for flying foxes, fragmenting their large nomadic populations into many small populations in urban and agricultural areas.

Importantly, the models showed a strong association between food shortages and clusters of Hendra virus spillover from these new abodes over the following year.

This means that by tracking drought and food shortages for flying foxes, we can get a crucial early warning of riskier times for the Hendra virus – up to two years in advance.

Biosafety, veterinary health and public health authorities can use this information to alert horse owners to the risk. Horse owners can then ensure that their horses are protected with the vaccine.

How can we stop the virus-jumping species?

Conservationists have long pointed out that human health depends on a healthy environment. This is a very clear example. We found that the Hendra virus never jumped from flying foxes to horses when there was abundant winter nectar.

Protecting and restoring bat habitat and replanting key tree species away from horse pastures will improve bat health and keep us safer.

Flying foxes will leave roosts in cities or rural areas if there is abundant blooming gum elsewhere. It won’t be long — trees planted today could start attracting bats within a decade.

SARS-CoV-2 won’t be the last bat virus to leap across species and rock the world. Experts are planning ways to better respond to the next pandemic and are working on human vaccines based on Hendra’s equine vaccines. We can help too.

How? By restoring and protecting the natural barriers that have protected us for so long from bat-borne viruses. It is much better to prevent viruses from spreading in the first place than to do everything possible to stop a potential pandemic once it has started.

Planting trees can help prevent dangerous new viruses from reaching us. It really is that simple.

More information:
Peggy Eby et al, Pathogen spillover driven by rapid changes in bat ecology, Nature (2022). DOI: 10.1038/s41586-022-05506-2

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