June 1

Where Do Deadly Coronaviruses Like MERS-CoV Come From?


Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

It was December 30, 2019—New Year’s Eve eve—when Dr. Li Wenliang, an ophthalmologist at Wuhan Central Hospital in the Hubei province of China, messaged his fellow physicians alerting them to the appearance of a concerning cluster of pneumonia cases. In response, he was detained for “spreading rumors,” summoned to the Public Security Bureau, and reprimanded for “making false statements that disturbed the public order.” Thirty-nine days later, after becoming infected with the very virus he tried to warn his colleagues about, he was dead at age 33. By that time, the disease had already spread to dozens of countries. My new book How to Survive a Pandemic is dedicated to Dr. Li’s memory.

His initial message read “7 SARS cases confirmed at the Hoo-ah-nin Seafood Market.” SARS stands for Severe Acute Respiratory Syndrome, which, seventeen years earlier, had been the first deadly global outbreak triggered by a coronavirus. (Sadly, the doctor who first alerted the world to that epidemic, Carlo Urbani, also succumbed to the disease.)

Coronaviruses are named for their crown-like appearance under an electron microscope—from the Latin corona, for “crown,” as in coronation—due to a fringe of protein spikes that radiate from the surface. I’m sure you’ve all seen those graphical representations, but this is what they actually look like under an electron microscope. You can see that halo of spikes. These are actually chicken coronaviruses, the first type of coronavirus ever discovered, which cause a disease called avian infectious bronchitis. Here’s the COVID-19 coronavirus. It’s a little hard to see the spikes, but they show up nice in this colorized version.

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Before the big outbreak of SARS in 2003, only two coronaviruses were known to cause disease in humans, and both caused little more than the common cold. But the SARS coronavirus went on to kill nearly one in ten people it infected––a 10 percent mortality rate.

A decade later, in 2012, another deadly coronavirus emerged: MERS, the Middle East respiratory syndrome coronavirus. Like SARS, MERS spread to infect thousands of people across dozens of countries, but this time, one in three died. More than a 30 percent mortality rate!

Emerged, from where? Where do emerging infectious diseases emerge from? According to the CDC, three-quarters of new or emerging infectious diseases in people come from animals, based likely on this landmark study of the risk factors for human disease emergence, and it may be an even greater percentage for human viral infections––all of which may have originated in animals, been zoonotic in origin, meaning an animal-to-human disease.

In the case of coronaviruses, most human coronaviruses appear to have arisen originally in bats. The reason bats make such good viral hosts is that up to 200,000 can crowd together in dense roosting colonies, and they can fly more than a thousand miles, acquiring and spreading new viral strains. Their unique navigational tool—echolocation—may even facilitate bat-to-bat transmission by spraying out respiratory secretions.

But people aren’t getting the diseases directly from bats. Bats are considered the primordial hosts, the “gene pool” from which genetic fragments of coronaviruses can mix and match. Breaching the species barrier to infect people appears to necessitate intermediary hosts in whom coronaviruses can adapt, amplify, and access human populations. In the case of MERS, the intermediate hosts were found to be camels.

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A bat in Saudi Arabia was found carrying the MERS coronavirus, but it is contact with the bodily fluids of infected camels—particularly their nasal secretions—that is considered the major risk factor for human infection. Once camels infect people, MERS can then be spread human-to-human.

Now of course, those in the camel business denied the link between MERS and camel exposure. In response to the warnings that those in close camel contact “wear proper personal protective equipment at all times” they launched with a social media campaign entitled, and I’m not making this up, Kiss Your Camel.

But wait, we domesticated camels 3,000 years ago. What happened to turn camel slobber into a potential kiss of death? Archived samples of camel blood show MERS had long been circulating in them for decades before spilling over into the human population. Why now?

Camels used to be allowed to forage outdoors, but as more and more camels were being raised, desertification from overgrazing forced the industry to transition to thousands of camel farms, using enclosed, high-density housing systems where they were confined indoors. And the high-intensity contact between camels alongside their workers is thought to be what helped drive the spillover of the MERS coronavirus from camels to humans. By 2011, open grazing was completely banned in Qatar, the Middle Eastern country with the highest camel density. The next year, the first human cases of MERS were reported.

In my next video, I’ll cover the emergence of the SARS coronavirus and then the emergence of SARS coronavirus 2, the cause of COVID-19.

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