Viruses in bats may have mixed and matched genes to create the virus that gave rise to the deadly SARS outbreak in 2003, a new study suggests. And it could happen again. All of the ingredients needed to create a new SARS virus are found among viruses currently infecting horseshoe bats, researchers report November 30 in PLOS Pathogens.
The viruses “are poised to cause future outbreaks,” says virologist Ralph Baric of the University of North Carolina School of Medicine in Chapel Hill, who was not involved in the study. “We can’t let our guard down.”
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Severe acute respiratory syndrome, or SARS, is caused by a type of coronavirus. After the first human case of SARS was recorded in 2002 in Guangdong Province in southern China, a global epidemic of the disease sickened more than 8,000 people and killed 774 in 2003.
In that outbreak, masked palm civets sold in live animal markets passed the virus to people. It wasn’t clear whether civets were the initial source of the virus, or if they caught it from some other animal. Since then, evidence has been building implicating species of horseshoe bats as the origin (SN: 11/30/13, p. 13). Until now, though, coronaviruses isolated from bats were genetically distinct from the one that caused the 2003 outbreak, suggesting that bat strains weren’t the direct ancestor of SARS.
After five years of surveying bats in a cave in southern China’s Yunnan Province, Zhengli Shi and colleagues discovered 11 new strains of SARS-related viruses in horseshoe bats (especially in Rhinolophus sinicus). Within the strains, the researchers found all the genes to make a SARS coronavirus similar to the epidemic strain, says Shi, a virologist at the Wuhan Institute of Virology, Chinese Academy of Sciences.
These new strains are more similar to the human version of SARS than were previously identified bat viruses, says Matthew Frieman, a virologist at the University of Maryland in Baltimore.
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By analyzing the new viruses’ complete genetic makeup, Shi and her colleagues retraced the steps that might have given rise to the original SARS virus. A few spots in the viruses’ DNA seem particularly prone to rearrangement, so remixing happens often. The study suggests that recombination between viruses has shaped the evolution of SARS, says Baric.
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,” Frieman says. “Whether they will or not is anybody’s guess.”
Trying to head off that jump by getting rid of the bats is not a solution, say Frieman and Baric. Bats perform many important ecological tasks, such as eating insects and pollinating some plants. Coronaviruses don’t make bats sick, so studying bats’ immune systems, Frieman says, could give scientists clues about how to fight the illness.
Editor’s note: This story was updated December 11, 2017, to delete the description of masked palm civets. They are not cats.