Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. Many of us are feeling helpless in the face of the current pandemic. But the good news is there’s things we can do right now to reduce our risk of falling seriously ill and dying from COVID-19 and preventing even greater infectious disease threats in the future.
We start our series – with an origin story – of the coronavirus. In the last 17 years, there have been three new deadly coronavirus epidemics, but where do emerging diseases emerge from?
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.
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 viralinfections––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.
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 our next story we discover the role live animal markets and the trade in exotic animals have played in the emergence of deadly coronavirus outbreaks.
SARS was the first new global disease outbreak of the 21st century, which went on to cause about 8,000 cases and about 800 deaths. Many of the first cases of SARS were tied to the same kind of place most of the first cases of COVID-19 were linked to: live animal “wet” markets in China.
Freshly slaughtered animals are thought to be more nutritious by many regional consumers, and some seek ye-wei, the “wild taste,” believing the consumption of exotic animals bestows benefits to health and social status. This convergence—fresh slaughter with exotic animals—leads to a perfect storm for disease transmission, where crowded cages in these wet markets are contaminated with the blood, urine, and feces of countless species mixed together in a potential cauldron of contagion.
There was a vast expansion of the wildlife trade in the 1990s to supply the emerging urban middle-class demand, driven, according to the World Bank, predominantly by demand for wild animal products in China. Many of the wild animals, typically while alive, enter China through Vietnam from Laos, where the wildlife meat trade rose to become the second-largest income source for rural families. Markets there sell a ton of animals (literally), many of which are critically endangered.
Then, as demand surpassed supply, the cross-country wildlife trade was supplemented with the creation of intensive captive production farms, where a menagerie of wild animals are often raised under poor sanitation in unnatural stocking densities before being transported and caged at markets for sale. Fourteen million people are involved in China’s wildlife farming industry, valued at 74 billion dollars.
The genetic building blocks for the SARS virus have since been identified from 11 different strains of coronaviruses found in Chinese bats, but there are bat-borne coronaviruses around the world. The reason China in particular has been ground zero for multiple jumps of deadly human coronavirus epidemics may be because of these wet markets.
In the case of SARS, the intermediate host appeared to be the masked palm civet, a cat-like animal prized for its meat. In addition to being raised for their flesh, civet cat penis is soaked in rice wine for use as an aphrodisiac. These animals also produce the most expensive coffee in the world. So-called fox-dung coffee is produced by feeding coffee beans to captive civets and then…recovering the partially digested beans from their feces. I don’t know if you can see, but those are actually civet turds. “A musk-like substance of buttery consistency secreted by the anal glands gives the coffee its characteristic flavor and smell.” One might say this unique drink is good to the last dropping.
Coronaviruses acquired from civets in live animal markets were almost identical to the SARS virus. While civets at wildlife farms supplying the live markets were found largely free of infection, up to 80 percent of sampled civets at the markets showed evidence of exposure. This suggests that most infections happened at the market, perhaps due to a combination of crowded interspecies mixing and the immunosuppressive effect of stress.
Live animal markets not only allow for cross-species transmission, viral amplification, and human exposure, but viral modification too. The SARS coronavirus exploited opportunities provided by wet markets in southern China to adapt to the palm civet and human. Apparently, civets were not just passive conduits for the virus; they appear to be incubators for human-adapting mutations in the virus itself.
The virus uses its corona of spikes like a key in a lock to latch onto host receptors to gain entry into its victims’ cells. To switch from infecting one species to another, the genes that code for the spikes have to mutate to fit into the new host’s receptors. A new lock requires a new key.
Both the SARS coronavirus and SARS coronavirus 2, the virus that causes COVID-19, attach to a specific enzyme coating the cells of our lungs. By the time a mishmash of bat coronaviruses made it into civets, the docking spikes of the virus were only two mutations away from locking in the configuration that bound to human receptors, and then the human-to-human SARS epidemic was born.
After the initial SARS outbreak ended in 2003, new human cases were confirmed, tied to a restaurant serving civets. Unlike most of the previous cases, the new victims presented with mild symptoms, and didn’t seem to pass it on. Viruses sampled from palm civets at both a local market and the restaurant were found to be nearly identical to those discovered in the new, milder human cases. The new civet viruses shared only one of the two civet-to-human spike mutations found in all of the new human patients, but none of the previous year’s civet’s coronaviruses. These findings suggest that intermediate hosts can help transform coronaviruses from the primordial reservoir in bats into greater human infectivity.
Yes, bats are trapped for meat in Asia, and many bat hunters do report getting bitten. Yes, the handling and consumption of undercooked bat meat is still practiced in China, Guam, and other parts of Asia. But it appears intermediate hosts may be needed as a stepping stone for bat coronaviruses to adapt to humans to trigger a human pandemic. And it’s hard to imagine a system that could be better designed to facilitate this process than a live animal wet market.
In response to the SARS outbreak, the Chinese government implemented strict controls over the wildlife market, including a ban on the sale of civet cats. Though the permanent closure of live animal markets has been called the “strongest deterrent to another zoonotic disease outbreak,” within months, the ban was lifted, and trade resumed as before. Civets were back on the menu.
Had authorities in China learned its lesson from SARS and listened to experts and enacted a permanent ban on live animal markets, it’s possible humanity would not now be suffering the worst pandemic in a century.
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For a vital, timely text on the pathogens that cause pandemics, you can order the e-book, audio book, or actual book of my latest book, “How to Survive a Pandemic.”
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