Dec. 12, 2012 -- The SARS-like coronavirus that has killed five people and sickened four more has some important -- and possibly dangerous -- differences from the virus that caused the deadly 2003 SARS outbreak, researchers reported.
The new virus -- dubbed hCoV-EMC -- appears to be able to infect a wide range of mammalian cells, including those of bats, according to Dr. Christian Drosten of the University of Bonn Medical Center in Bonn, Germany, and colleagues.
That could mean it has a natural host in the wild and a relatively low barrier against cross-species transmission, Drosten and colleagues reported online in mBio.
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Other coronaviruses that infect humans -- including the SARS virus -- began as bat pathogens, but lost the ability to infect the flying mammals when they adapted to humans, the researchers noted.
SARS, in particular, is no longer present in the wild and can't pass back and forth from bats to humans. "The (SARS) virus lost its old host and gained a new one," Drosten said in a statement.
The "quite remarkable" range of possible targets for hCoV-EMC suggests that humans might repeatedly acquire the virus, Drosten and colleagues reported.
There have been only a handful of confirmed infections by hCoV-EMC, according to the World Health Organization.
As of Nov. 30, the agency said, there have been nine cases -- two in people from Qatar, five in residents of Saudi Arabia, and two in Jordan. Of those, five ended in death.
There is also some limited evidence of human-to-human transmission, the agency said.
The first two cases in Saudi Arabia were not linked to each other, but the remaining three were members of a single family living in the same household. The two cases in Jordan were found by screening stored samples from a cluster of pneumonia cases in April 2012.
The novel virus rang alarm bells because it is genetically akin to the SARS virus, which caused hundreds of deaths worldwide and because, like SARS, it led to severe respiratory illness with renal failure.
"This virus is closely related to the SARS virus, and looking at the clinical picture, it causes the same pattern of disease," Drosten said.
Given the similarities, the researchers wanted to know if hCoV-EMC used the same receptor to infect cells – angiotensin-converting enzyme 2 (ACE2).
The fact that SARS used that receptor is credited with both the aggressive course of disease and with the relatively slight population-level impact, the researchers noted.
On the one hand, the receptor is expressed on pneumocytes that are deep in the respiratory tract of humans -- but only rarely on cells higher up -- so that a large dose of virus was needed for infection, leading to aggressive disease.
On the other hand, the severe symptoms meant that victims were quickly admitted to the hospital and isolated, possibly limiting wider spread of the disease.
The ability of the virus to infect bats "was a big surprise," Drosten said. "It's completely unusual for any coronavirus to be able to do that -- to go back to its original reservoir."
The findings also mean it's possible that hCoV-EMC could use a receptor in the human lung that is easier to access, which might make it easier to catch and transmit than SARS.
But, the researchers reported, they still don't know what receptor the virus does use, except that it must be present in all three types of mammals.