10/30/2013 02:01 EDT | Updated 01/23/2014 06:58 EST

SARS-like viruses found in Chinese bats; closest hit yet to 2003 outbreak virus

TORONTO - A consortium of international scientists has discovered a SARS-like virus recovered from a Chinese horseshoe bat, further solidifying the theory that these bats are the ultimate source of the virus that killed more than 900 people around the globe in 2003.

The new virus, which they called WIV1, is the closest match yet between SARS and coronaviruses from bats. In fact, the viruses are close enough genetically that antibodies in stored blood samples from SARS patients neutralized the virus in seven of nine samples tested.

The scientists also reported that the virus uses the same receptor — called ACE2 — to latch onto and infect cells that SARS does. In laboratory work, WIV1 was able to directly infect human cells.

That, they suggested, means that viruses like this may not need an animal go-between to cause human outbreaks — they may be able to jump directly from bats to people.

"Intermediate hosts many not be necessary for direct human infection by some bat SL-CoVs," they wrote in the paper, which is published in the journal Nature. (SL-CoVs is short for SARS-like coronaviruses.)

Other scientists, though, cautioned that just because something occurs in the artificial confines of a laboratory doesn't mean it would also happen readily in nature.

"We've known for a long time that bats carry all sorts of dangerous viruses. Yet we don't all die," said Marion Koopmans, chief of virology in the Dutch National Institute of Public Health's Center for Infectious Disease Control.

"Cells in a test tube in the lab are very different from cells in a human host."

Koopmans said even if it isn't essential to have another animal serve as a bridge — the way infected civet cats did in Chinese animal markets during SARS — it may remain more likely that bat viruses might take an indirect route into the human population.

"It may not be essential to have an in-between host, but it may be that if bats carry viruses that easily infect intermediate hosts, that their ability to get to humans is much greater," she said.

Michael Osterholm agreed.

The director of the Center for Infectious Diseases Research and Policy at the University of Minnesota, Osterholm said a factor that needs to be considered is how bat viruses could come in contact with human cells.

In other words, what body fluid from the bat — saliva, urine, feces, blood — carries and therefore can transmit the virus?

"If the primary body fluid involved with transmitting (bat) coronaviruses to other animal species or humans is feces, the question becomes: How often is that likely to occur?" Osterholm asked.

Peter Daszak, co-senior author of the paper, said it is true that this type of viral species jump is uncommon. But he said as humans encroach on the habitat of bats and other wild species, the risk rises.

"There are many, many thousands of people — millions — in China who live close to bats. The problem is that we're doing things that put us at risk. And we're increasing those. So we're increasingly catching bats, bringing them into the wildlife (meat) trade and eating them globally,'' said Daszak, a disease ecologist who is president of the conservation group Ecohealth Alliance.

"So yes, the risk is low. But actually, multiply that by billions of people and multiply it by an increasing annual encroachment into forest and an increasing connectivity with wildlife, and the risk grows."

The finding resulted from work done in China's Yunnan Province. The scientists gathered feces and collected fecal swabs from horseshoe bats over the course of 12 months from April 2011 and September 2012.

Of 117 samples, 23 per cent were positive for coronaviruses. Genetic sequencing of RNA from the samples showed evidence of seven different strains of coronaviruses. The scientists were able to generate genetic sequences for two, which were a 95 per cent match for a SARS virus known as Tor2. (Its name indicates it was isolated from a Toronto SARS patient.)

But WIV1 was the only live virus they were able to extract from the material. Daszak said this is the first time, to his knowledge, that has occurred.

They tested the virus to see if it could grow in a wide variety of different types of cells from different species — human respiratory tract and pig kidney cells among them. The virus grew in a surprising number, though not all.

German coronavirus expert Christian Drosten was involved in a study published last year that showed the MERS coronavirus — a SARS cousin — had a similar ability to infect cells from a diverse number of animal species. At the time, Drosten and his co-authors reported this was a rare feature of MERS, which is the virus behind the ongoing outbreak in the Middle East.

Drosten said seeing similar behaviour in this new virus suggests some coronaviruses probably pose more of a risk to humans than others because they have more potential to jump species.

"Here we have a big challenge for future research: to discriminate those potentially dangerous viruses from those that are ... most likely harmless because they are restricted to their hosts," Drosten said in an email.

The work was done by scientists from the Wuhan Institute of Virology of the Chinese Academy of Sciences, Ecohealth Alliance, the University of California, Davis, the CSIRO Australian Animal Health Laboratory at Geelong, East China Normal University at Shanghai and Duke-NUS Graduate Medical School in Singapore.