A decade after SARS swept through the world and killed more than 750 people, scientists have made a troubling discovery: A very close cousin of the SARS virus lives in bats and it can likely jump directly to people

Study: Bat-to-Human Leap Likely for SARS-Like Virus

GAUTAM NAIK

Updated Oct. 30, 2013 7:07 p.m. ET

A decade after SARS swept through the world and killed more than 750 people, scientists have made a troubling discovery: A very close cousin of the SARS virus lives in bats and it can likely jump directly to people. The findings create new fears about the emergence of diseases like SARS, or severe acute respiratory syndrome. The virus spread quickly from person to person in 2003 and had a mortality rate of at least 9%. Worries of a severe pandemic led the World Health Organization to issue an emergency travel advisory.While bats have previously been fingered as a host for SARS, it was believed that the virus jumped from there to weasel-like mammals known as civets, where it went through genetic changes before infecting people. Operating on that belief, China cracked down on markets where bats, civets and other wildlife were sold for food.

The new bat-to-human discovery suggests that the control tactic may have limited effectiveness because a SARS-like virus remains loose in the wild and could potentially spark another outbreak.

“It changes the equation” for public health, said Peter Daszak, a senior author of the study and president of EcoHealth Alliance, a group involved in conservation and global health. “We can close all the markets in China and still have a pandemic.”

The latest findings, published in the journal Nature on Wednesday, may also help scientists grapple with a more immediate worry. About a year ago, a novel SARS-like virus was reported in the Middle East. It has since killed more than 50 people and some preliminary research suggests that it also may have originated in bats.

SARS is caused by a germ known as a coronavirus. First discovered in 2003 in southern China, SARS went on to sicken more than 8,000 people in more than two dozen countries in North America, South America, Europe and Asia, before it was contained. No known cases have been reported anywhere since 2004.

But a key puzzle remained. No one ever found a live SARS virus in bats found in southern China’s wildlife markets, making it unclear that those bats were the source. So where did it come from?

Dr. Daszak and his colleagues chose to study a horseshoe bat colony in Yunnan province in southwest China—hundreds of miles from the big wildlife-for-food markets of Guangdong province, where SARS was first reported.

The researchers took hundreds of samples from the horseshoe bats. A genetic analysis revealed at least seven different strains of SARS-like coronaviruses circulating in that single group of animals.

Crucially, the scientists were also able to isolate and culture a live virus that binds to a receptor on a human cell. That suggests that direct bat-to-human infection would likely occur.

“This paper indicates that the bat is the origin and that the virus can be directly transmitted to humans,” said Charles Calisher, a virologist at Colorado State University, who wasn’t involved in the study. “It practically rules out the possibility” of an intermediate host.

Dr. Daszak described a potential scenario where close contact between bats and humans—such as when the animals are captured for food—could increase the risk of viral transmission. “They are bringing wildlife in from new areas. They are going to Yunnan where bats are still common.”

Dr. Calisher said the finding was important because researchers will now be able to get important clues about the danger these novel SARS-like coronaviruses pose. For example, if a bat carries a high load of the virus, it indicates that the potential for transmission to humans is also high.

The U.S. Agency for International Development has a project that tries to identify emerging infectious diseases that may pose a threat to human health. One target: bats. Not much is known about the flying mammals, since they are nocturnal and often hard to find. But there is strong evidence that bats are a natural reservoir for a host of dangerous viruses, including Ebola, Nipah and SARS.

A year ago, scientists reported the emergence of a novel coronavirus, called Middle East Respiratory Syndrome, or MERS. It has since been reported in people in several countries, including Saudi Arabia, Germany, France, Italy, Britain and other parts of the Persian Gulf. Oman reported its first case on Wednesday, according to local reports.

In July, a WHO committee concluded that while MERS was of “serious and great concern” it wasn’t a global health emergency. Research has suggested local bats may be a host for MERS, though the findings aren’t definitive.

Nonetheless, the authors of the Nature study noted that the outbreak in the Middle East “suggests that this group of viruses remains a key threat and that their distribution is wider than previously recognized.”