In a new study, researchers sought to provide more granular data collected over 25 years in Australia to illustrate the links between habitat loss, animal behavior and viral spread.
Specifically, scientists looked at the Hendra transmitted by bats virus, which primarily infects fruit bats (also called flying foxes); the virus can spread to humans via horses.
“Interactions between land-use change and climate now lead to the persistent residence of bats in agricultural areas, where periodic food shortages lead to clusters of fallout,” said behavioral ecologist Peggy Eby of the University of New South Wales in Australia and his colleagues. write in their published article.
Zoonotic fallout describes how viruses and other pathogens found in animals can spread to humans, sometimes with deadly consequences. The Hendra virus is an example; HIV, Ebolarabies and plague make a grim shortlist of other zoonotic diseases.
Hendra virus – named after the suburb of Brisbane where it was discovered in 1994 – can cause serious illness, even death, in humans and horses. Most commonly, infected bats feeding in horse paddocks transmit the virus, and since 2006 the frequency and extent of Hendra virus spillovers in Australia have increase.
In this study, Eby and his colleagues drew on decades of data to investigate rapid changes in bat behavior that coincided with Hendra virus spread events in South West Queensland between 1996 and 2020. the timing and location of these events were mapped against data on bat roosts, foraging areas, local climate, food supplies, and habitat loss.
“From about 2003 to 2020, bat behavior and spillover incidence changed rapidly: the number of roosts tripled and 40 spillovers were detected,” Eby and colleagues report.
By fitting the data to a statistical model, the researchers showed how changes in climate and land use push bats to live in agricultural and urban areas, increasing the risk of spreading the Hendra virus to horses.
By 2018, nearly a third of the natural habitat for fruit bats in 1996 had been cleared, sending bats flocking to urban areas to roost, although most spillover events (86%) occurred in agricultural areas where horses roam.
Drought-inducing El Niño events have also caused winter food shortages for bats, heralding an increase in roosts closer to human-populated areas where bats could likely find food.
Not only are food shortages and habitat loss pushing bats into areas where humans and horses live – increasing the number of human-animal encounters – but previous research suggests nutritional stress can lead to increased viral shedding in bats.
“The timing of the Hendra virus spread clusters in winter, months after the previous year’s food shortages, may be due to the cumulative effects of nutritional stress overlaying high winter energy requirements (thermoregulation and pregnancy) and scarce resources in suboptimal habitats,” the researchers write.
When nearby native forests bloomed profusely in winter – which is becoming increasingly rare – the bats reverted to their usual nomadic lifestyle, leaving urban and agricultural areas in favor of their natural habitat, and no events of overflow did not occur during these times.
Protecting remnants of native forests, especially winter flowering forests that provide food when food is scarce, “could be a sustainable long-term strategy to reduce fallout and protect livestock and human health,” according to the researchers. conclude.
Replicating a study like this in other regions where zoonotic diseases are common could reveal the dynamics that contribute to these outbreaks and inform strategies to reduce the risk of infections.
But long-term data going back decades on viral reservoir hosts, especially bats, is sparse. And even with our data, it keeps coming back to the same problem: humans are constantly destroying habitats and bulldozing biodiversity.
A Analysis 2020 of approximately 6,800 ecological communities on 6 continents have found that as biodiversity declines, animals that survive and thrive, such as bats and rats, are also most likely to harbor potentially dangerous pathogens , which concentrates the risk of zoonotic disease outbreaks.
“We’ve been warning about this for decades,” said Kate Jones, an ecological modeler at University College London and co-author of the study. Told Nature when published in August 2020.
“No one paid attention to it.”
The latest study was also published in Nature.