"The SARS Coronavirus and Wet Markets"
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 convergenceâ€”fresh slaughter with exotic animalsâ€”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 actually 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% 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 humans.
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 civets' 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 that 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.