Climate Crisis

One popular bat Covid-19 theory may actually be true — study

We should have seen it coming.

Eastern Tube nosed bat in care at The Bat Hospital, Atherton, Far North Queensland.

For decades, scientists have been sounding the alarm on the rise in infectious diseases caused by climate change.

But despite bird flu, swine flue, mad cow disease, ebola, and more, these pleas were largely ignored by policymakers and the general public — until a coronavirus called SARS-CoV-2 jumped from animals to humans. And now here we are, at the one-year anniversary point of a global pandemic that has upended life as we knew it.

The trigger species has long been presumed to be bats — but exactly how the virus made the leap, and why, has been the subject of debate. Climate scientists would tell you it was our own fault, pushing into bats' wild habitats and bringing ourselves in to too close contact with the animals which carry these viruses.

Turns out, they are — at least in part — absolutely right. New research published Friday in the journal Science of the Total Environment provides concrete evidence for the theory SARS-CoV-2, which causes Covid-19, originated in bats.

Perhaps more importantly, the study explicitly links climate change to the uptick in bat species carrying coronavirus in China's Yunnan province, as well as in neighboring countries like Laos and Myanmar.

Robert Beyer is a researcher in the University of Cambridge's Department of Zoology and first author of the study. He tells Inverse Covid-19 may be just the first stop on a dangerous trajectory.

"There is strong evidence that climate change will further shift the geographic ranges of many of the world's species, which can put them, and the viruses they carry, into contact with new species that can result in novel viral transmissions," Beyer says.

Flower fields in the Yunnan province -- an area of high interest in the study.


How they did it — Using pre-existing data, the researchers first established the geographical ranges of individual bat species in both the early 20th century and the present day.

Ultimately, they created a global map showing vegetation coverage and then compared these data to the amount of vegetation coverage each individual bat species require. They also considered how other environmental factors may have changed over time, too, like average monthly temperature, rainfall, and cloud cover between 1901 and 2019.

"In this way, we es­ti­mated the global dis­tri­b­u­tion of nat­ural veg­e­ta­tion based on the cli­matic con­di­tions in the early 20th cen­tury and at pre­sent," the authors write in the study.

This method enabled the scientists to figure out the global distribution of bat species through 1901 and 2019.

What's new — The researchers found many regions of the world — including parts of Central Africa, Central and South America — have experienced significant increases in bat species as a result of climate change.

Zooming in on the southern Chinese province of Yunnan, as well as the countries of Laos and Myanmar, the researchers found what they call a "hotspot" for these zoonotic diseases.

"This lat­ter hotspot co­in­cides with the re­gion cur­rently con­sid­ered as the most likely ori­gin of the bat-borne an­ces­tors of SARS-CoV-1 and SARS-CoV-2."

Specifically, there was an increase of approximately 40 bat species across this region.

The researchers assume each bat species carries 2.67 coronaviruses — with that assumption, they theorize there is an increase of some 100 bat-borne coronaviruses in this area of China and Southeast Asia.

Why it matters — From Ebola to SARS-CoV-1, bats have long been linked with the rise in infectious diseases. But it's only with the rise of Covid-19 that the general public became strongly aware of the possible connections between climate change and novel coronaviruses.

According to the study, increases in carbon dioxide levels over the last century drastically altered the vegetation in the Yunnan province and other regions.

Greenhouses gases have transformed these areas from tropical shrubland to savannah, and deciduous woodland — forest environments are excellent habitats for bats to thrive.

Bat species increasingly populated these habitats, leading to greater opportunity for animal-human interactions. By understanding changes in bat habits, we can better understand the environmental conditions that gave rise to SARS-CoV-2.

"As climate change altered habitats, species left some areas and moved into others — taking their viruses with them. This not only altered the regions where viruses are present, but most likely allowed for new interactions between animals and viruses, causing more harmful viruses to be transmitted or evolve," Beyer says.

Digging into the details — Importantly, the margin of error in this study is plus or minus 50 coronaviruses, so take the results with a pinch of salt. Ultimately, however, one thing remains: There are more bat-borne coronaviruses in the region, and climate change is the driving mechanism for their increase.

Somewhat surprisingly, the data found that climate change wasn't as strongly linked to some prior coronavirus diseases like MERS-CoV — which likely originated from bats in East Africa — suggesting perhaps increases in bat-driven coronaviruses occur in very specific parts of the globe prone to climate change habitat shifts.

A figure from the study showing global bat distribution.

The study also doesn't give us hard evidence on an intermediary species — like a pangolin — that allowed SARS-CoV-2 to jump from bats to humans.

"Our analysis doesn't necessarily confirm or challenge the hypothesis that pangolins were an intermediate species," Beyer says.

A figure from the study illustrating changes in bat habitats.

What's next — As mentioned above, the study is not without its limitations. The model focuses specifically on climate change linked to vegetation use without considering other factors — such as land use changes or pollution — that may be contributing to changes in bats' habitats, too.

"In other words, the approach is specifically designed to isolate the effect of climate change on bat habitat ranges," Beyer says.

For example, habitat destruction vis-a-vis deforestation has made the likelihood of pandemics more prominent. We also cannot say for certain whether the increase in bat species will lead to future pandemics originating from the Yunnan province, Laos, or Myanmar.

But the study's message is clear: Humans must act quickly to curb climate change and reduce the opportunities for animal-human coronavirus transmission, or we may find ourselves in another global pandemic in short order.

"Combined with urban areas, farmland and hunting grounds further expanding into natural habitats, and thus creating new opportunities for contact between humans and pathogen-carrying animals, this makes it plausible that we will see more zoonotic outbreaks in the future," Beyer says.

Actions suggested in the study include:

  • Imposing strong reg­u­la­tions on wildlife hunt­ing and trade
  • Es­tab­lishing ap­pro­pri­ate an­i­mal wel­fare stan­dards on farms
  • Dis­cour­aging high-zoonotic-risk di­etary and med­i­c­i­nal cus­toms

"The fact that climate change can accelerate the transmission of wildlife pathogens to humans should be an urgent wake-up call to reduce global emissions," Professor Camilo Mora at the University of Hawai'i at Manoa, who initiated the project, said in a press statement accompanying the results.

Correction: This article originally stated an incorrect location for Wuhan, which is in Hubei Province, China. We regret the error.

Abstract: Bats are the likely zoonotic ori­gin of sev­eral coro­n­aviruses (CoVs) that in­fect hu­mans, in­clud­ing SARS-CoV-1 and SARS-CoV-2, both of which have caused large-scale epi­demics. The num­ber of CoVs pre­sent in an area is strongly cor­re­lated with lo­cal bat species rich­ness, which in turn is af­fected by cli­matic con­di­tions that drive the ge­o­graph­i­cal dis­tri­b­u­tions of species. Here we show that the south­ern Chi­nese Yun­nan province and neigh­bour­ing re­gions in Myan­mar and Laos form a global hotspot of cli­mate change-dri­ven in­crease in bat rich­ness. This re­gion co­in­cides with the likely spa­tial ori­gin of bat-borne an­ces­tors of SARS-CoV-1 and SARS-CoV-2. Ac­count­ing for an es­ti­mated in­crease in the or­der of 100 bat-borne CoVs across the re­gion, cli­mate change may have played a key role in the evo­lu­tion or trans­mis­sion of the two SARS CoVs.
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