June 3

The SARS Coronavirus and Wet Markets

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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.

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.

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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.

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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.

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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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