Single Population of Bats Possessing all “Ingredients” for SARS Epidemic
Bats are shoddy as it is.
Just as researchers feared, the virus behind the deadly severe acute respiratory syndrome (SARS) epidemic of 2003 is still out there: A Chinese Academy of Sciences group has now discovered that viruses that have infected horshoe bats in China could cause the next major SARS outbreak.
The original SARS outbreak, which killed more than 700 people around the world and sickened over 8000 in the winter of 2002-2003, was traced to weasel-like animals called masked palm civets being sold at live animal markets in southern China. Researchers suspected that civets were just a conduit and not the real reservoir for the SARS virus because it was not found in civets on farms or in the wild. Subsequent sequencing analyses traced the virus to bats and civets. In 2013, an international team of researchers found that horseshoe bats in a cave in China’s Yunnan Province harbored coronaviruses that resembled the human SARS-coronavirus, but with some key differences.
That team, led by the Chinese Academy of Sciences’ Zheng-Li Shi, has monitored the cave for five years, collecting bat viral samples. The team found distinct bat coronaviruses within that cave that — when put together — had all the genetic pieces of the human SARS-CoV. This suggested to the team that the ancestor of the human SARS-CoV arose through recombination of the bat viruses before spilling over into an intermediate host, possibly the civet.
“As a whole, our findings from a five-year longitudinal study conclusively demonstrate that all building blocks of the pandemic SARS-CoV genome are present in bat SARSr-CoVs from a single location in Yunnan,” Shi and her colleagues wrote in their paper.
In all, the team identified 11 new strains of SARS virus carried by the bats, and a genomic analysis of these – along with strains from the same cave identified in previous research – revealed something interesting.
In the new research, that held true again – none of the viruses from the cave by themselves displayed the genetic traits of the SARS coronavirus that spread to humans, infecting more than 8,000 people during the 2002-2003 emergency.
But together, it was a different story. In this one cave, there were enough genetic ingredients among the strains to build the virus that kills humans.
The researchers sequenced the full genomes of 11 of the novel SARSr-CoV strains they found in the cave. These genomes ranged in size from 29,694 nucleotides to 30,291 nucleotides. When combined with the four viruses the researchers previously uncovered in this cave, they calculated that the SARSr-CoVs circulating there shared between 92 percent and 99.9 percent sequence identity. Similarly, they were between 93.2 percent and 96 percent similar to human and civet viruses.
“Importantly, all of the building blocks of SARS-CoV genome, including the highly variable S gene, ORF8 and ORF3, could be found in the genomes of different SARSr-CoV strains from this single location,” the researchers explain in their paper.
Hypothetically speaking, the team suggests it’s possible – even probable – that if the right strains mixed with one another in the cave, you’d end up with the direct ancestor of a virus that can infect and kill people.
Several of the strains could already grow in human cells, Shi’s team found. That indicates “there’s a chance that the viruses that exist in these bats could jump to people,” says Matthew Frieman, a virologist at the University of Maryland in Baltimore. “Whether they will or not is anybody’s guess.”
Although the bats could become a threat to human life, researchers say that exterminating the species is not a viable solution. That’s because bats play an essential ecological role in their habitats, like pollination. They plan to continue to study the species to learn more about how the virus operates and possibly prevent future SARS outbreaks.
