Coronavirus – Credit CDC PHIL
While we wait for more information on the novel coronavirus that continues to pop up in the Middle East (see WHO Announces Additional Coronavirus Cases), it isn’t lost on most infectious disease geeks that this month (November) marks the 10th anniversary of the initial outbreak of SARS in Guangdong Province, China.
Over the next eight months SARS (Severe Acute Respiratory Syndrome) infected more than 8,000 people, killing roughly 10%. China, Hong Kong, and Taiwan were the hardest hit, but a handful of cases made it into Canada, the United States, and across Europe.
Source World Health Organization
By mid-April of 2003 we learned the illness was due to a novel coronavirus (SARS-CoV). A bit of a surprise really, since human coronaviruses had previously only been linked to mild respiratory illnesses.
Although eventually contained, SARS was the first genuine pandemic threat of the 21st century. It also served to remind us that influenza isn’t the only virus with pandemic potential.
One of the most authoritative accounts of the SARS outbreak, and how it appears to have been linked to the practice of consuming bushmeat in China, comes from Karl Taro Greenfeld’s book The China Syndrome: The True Story of the 21st Century's First Great Epidemic.
While civet cats, which were served in `wild flavor’ restaurants in China, were first implicated in this outbreak (see A Civets Lesson), bats have also been shown to carry this Coronavirus, and may be the primary host.
The jury is out on whether the virus was transmitted directly to man from bats, or perhaps from bats to civits to humans.
Now the world is watching another coronavirus – definitely not SARS – but of the same general family, and capable of producing serious, even fatal illness in humans.
And like SARS, this new virus may be of bat-origin.
What we don’t know (yet) is the source of this virus, how it has managed to jump to at least 6 people in two countries, and whether – once contracted – it can be passed on to other humans.
Up until this week, the reassuring mantra has been that the virus does not transmit from human-to-human (H2H). The reason for that assumption has been the lack of nosocomial infection in hospitals where the first couple of cases were treated.
But this week we’ve learned of two family members in Saudi Arabia who tested positive for the virus, and that there were two other family members with similar symptoms, one of whom died.
One of the two additional family members tested negative, but we’ve little actual experience with the recently developed tests for this virus, and so its sensitivity isn’t well established. Tests are pending on the fourth family member who died.
Although a common environmental exposure is always possible, these latest revelations put H2H transmission back on the table.
The lack of human-to-human transmission in the earlier cases doesn’t rule out H2H transmission now, or in the future. When a virus jumps to a new species, it isn’t necessarily completely optimized for its new environment.
So one of the things we watch for are signs of further adaptation as the virus `figures out’ its new host.
Influenza viruses are the absolute master at this type of evolutionary adaptation, but are by no means the only virus with this ability.
One of the ways researchers test viruses is via a serial passage experiment. It is essentially how Ron Fouchier created a `mammalian-adapted’ H5N1 virus in the laboratory last year, and it mimics what viruses do in the wild.
Last year, in H5N1: A Rite Of Passage, I described how serial passage studies are conducted, but briefly, an experimental animal is infected with a virus, and that virus is then collected and used to inoculate another lab animal.
Simplified Illustration of a Serial Passage Experiment.
The process is repeated, and after 10 or so iterations, the virus is then examined for `adaptive changes’. Sometimes, after multiple passes through a series of hosts, the virus picks up mutations that favor its survival in the new species.
This process happens outside of the laboratory as well, which is why – when a virus jumps to a new species – we watch it carefully to see if it develops `legs’; the ability to spread efficiently.
Over the summer we watched as swine-variant H3N2v viruses tried – and for the time being, failed – to make a sustained jump to humans (see MMWR: H3N2v Related Hospitalizations In Ohio – Summer 2012). But past performance is no guarantee of future results.
There’s always next year.
And so it is with this new coronavirus. It could recede back into the woodwork, or it could sputter ineffectually for years, threatening occasionally - but never quite succeeding - as a major public health threat.
Or it could develop `legs’ and become the next big global health threat. At this point, no one knows.
For those looking for comfort, pandemics are a fairly rare occurrence. Many viruses emerge and threaten, but few are truly ready for prime time.
Like with H5N1, H3N2v, Nipah, and a handful of other emerging viruses that continue to make the occasional foray into the human population, we remain in a watchful waiting mode with this new coronavirus.
For more coverage of this developing story, I’d recommend Maryn McKenna’s blog from last night:
And finally, Crofsblog for the best news round up on the coronavirus, and many other EIDs.