Photo Credit NIAID
# 8630
Given that both diseases are caused by a previously unknown coronavirus, both appear to originate from an unusual zoonotic source, and both (so far) flourish and spread best in a hospital environment, it is tempting to believe that the MERS outbreak will follow pretty much the same course as did SARS in 2003.
Once that threat was recognized, quarantines were established, strict infection control procedures were implemented, and SARS was brought under control in a matter of months.
In the end SARS turned out to be a brightly burning, but relatively brief, epidemic that infected about 8,000 people – mostly in Asia - killing roughly 10% of them. But through a concerted international public health response, it was eventually contained.
While apparently the result of a zoonotic spillover, the exact host from which SARS entered the human population has never been firmly established. Many place the blame on the `wild flavor’ restaurants of Guangdong province - where customers could dine on exotic animals that were often kept alive, and in filthy cages, in the back kitchens awaiting their fate.
China’s belated response to the outbreak led to the shuttering of hundreds of these restaurants, the temporary closing of many `live markets’ dealing in `exotics’, and the culling of a prime zoonotic suspect – the Palm Civet (see A Civets Lesson). Something in this mix apparently worked.
Whatever its zoonotic origin, we were lucky that the SARS coronavirus wasn’t more common and widespread in the wild. As a result, the SARS virus disappeared and has not remerged in more than a decade, although similar coronaviruses have been detected in bats in Asia and the Middle East.
With MERS-CoV, while similar to the SARS virus in many ways, we may not be as lucky.
MERS-CoV appears to be endemic in a large (and geographically broad) population of camels – animals that are not only greatly beloved in the Middle East, but are often in close contact with humans (see Saudi Ministry Of Agriculture Issues Warnings On Camels).
While the exact role of camels in the spread of the disease has not been established, many researchers believe that they are responsible for intermittently introducing the virus to the human population (see CIDRAP NEWS WHO sees camels as MERS source, but route uncertain).
With SARS, once the zoonotic source was eliminated, solid infection control and quarantines were able to contain and quash the outbreak in humans.
If, as suspected, camels are the animal host through which the MERS virus gets into the human population - the likelihood is we will continue to see fresh introductions of the virus going forward.
Culling, which has previously been employed with chickens, ducks, and civets would be an impractical and extremely unpalatable option for millions of dromedaries, and a vaccine – assuming one would work with camels - may not be available for months or even years.
The only genuinely good news with MERS is that while human-to-human transmission is well documented, it doesn’t (yet) seem to transmit as readily as SARS did a decade ago. And it is far less transmissible than most other respiratory viruses (colds, flu, etc.).
In the short run, consistent strict infection control protocols and the proactive quarantining of exposed individuals – both used successfully to combat SARS - are likely to effectively contain localized outbreaks.
But unlike SARS, MERS-CoV has the potential to continually reseed itself into the human population. Localized outbreaks can therefore peak, be brought under control, only to fueled by another spillover event.
Meaning that even if MERS never gains an iota of additional transmissibility, it is unlikely we will see it fade from the international stage anytime soon.