14 May 2020
The complex role of wet markets and global health
In the wake of the COVID-19 pandemic, international debate is swirling over on the role of wet markets in China and whether they should be closed down to help prevent future zoonosis outbreaks or whether stricter regulation of the markets would be a better option.
China recently allowed some of its wet markets, which primarily sell vegetables and fresh (sometimes live) meat, to reopen after two months of temporary closures after the SARS-CoV-2 outbreak was linked to a market in the city of Wuhan.
Many in the West expected the WHO to oppose China’s decision and were surprised when the global organisation proffered the view that while many wet markets were poorly regulated and maintained, they continued to provide a source of affordable food and livelihood for millions of people.
“WHO’s position is that when these markets are allowed to reopen it should only be on the condition that they conform to stringent food safety and hygiene standards,” Dr Tedros Adhanom Ghebreyesus, the director general of the WHO, said, adding that “Governments must rigorously enforce bans on the sale and trade of wildlife for food.”
While the majority of wet markets in China sell only select live animals, particularly seafood, others do trade and slaughter wild animals such as bats and exotic and endangered species such as pangolins.
While these markets are not the norm in China and South East Asia, they are the focus of global concerns over the threats they pose to biosecurity and human health.
In early February, the Chinese government banned the sale of wildlife, either for consumption or other purposes, such as use in traditional Chinese medicines, in wet markets. But under these new rules, live animals which are more commonly farmed for food, such as chickens, pigs and fish, are still able to be slaughtered and sold in these markets.
So how much of a health risk are these markets?
Professor James Gilkerson, director of the centre for equine infectious diseases at the University of Melbourne, says any wet markets which allow the sale of any live animals have potential risk of zoonosis and should be banned.
“There have been many comparisons made of wet markets with farmers markets in Australia, but people go to farmers markets to buy fresh produce, it is not slaughtered in front of them at the market,” he says.
“What you’ve got at wet markets is a mixture of animals such as pigs, chickens and water birds like ducks and no understanding of how long they’ve been trussed up, how long it’s taken them to get to the market or how long they’ve been at the market.”
When animals are kept alive in a marketplace, they may have exposure to other wild and domestic animals enabling viruses to jump between species which would not normally come into contact with one another.
The risk of zoonosis is then further increased by these animals coming in contact with hundreds of people, working or shopping in the market.
“From a food safety point of view, it’s poor practice, and from a zoonotic point of view, it’s potentially dangerous,” Professor Gilkerson says.
Adding to the case for closing such wet markets is the history of previous zoonotic outbreaks of disease at these centres, such as the SARS pandemic in 2002 and the avian influenza (H7N9) outbreak in 2013.
“I think it’s wrong of the WHO to ignore that sort of risk, particularly when for decades the WHO have been very good about having evidence-based plans to try and mitigate these sorts of outbreaks,” Professor Gilkerson says.
At time of going to press, the precise origins of SARS-CoV-2 remained in doubt with China’s theory that the virus most likely was transmitted between animals and humans at a wet market in Wuhan was not universally accepted.
Associate Professor Ian Mackay, a virologist at the University of Queensland, says more investigation is needed to find the “missing strains” of the virus, which would explain how SARS-CoV-2 adapted between animals and humans to become the strain we now identify.
These strains, when discovered, could reveal the relationship between SARS-CoV-2 and a suspected parent virus, such as the bat coronavirus, RaTG13, providing an informed guide for prevention in the future.
Professor Mackay says these strains could potentially debunk the narrative that SARS-CoV-2 started at a wet market in Wuhan.
“China have primed their health surveillance to detect pneumonia of an unknown cause associated with a wet market because they don’t want to see another SARS event happen, which may have happened anyway, but it doesn’t mean that the outbreak started there,” he said.
An alternative theory is the virus could have been initially transmitted on a farm where different animal species were kept near bats.
“The prevention phase of future zoonosis will be to try and reduce contact between animals of different species and then also keeping humans away from those animals to reduce the risk of new and exotic viruses emerging,” Professor Mackay says.
This was the case for preventing the MERS coronavirus in Saudi Arabia, where effective prevention didn’t require a vaccine, rather it needed people to stay away from camels.
But this logic for public health prevention didn’t factor in the traditional culture of the Saudi people interacting with camels for racing, breeding and as pets.
The example with MERS shows it’s not just as easy as “let’s turn the faucet off and close wet markets,” when human habits and traditions are involved, and often these traditions are hard to break, Professor Mackay says.
It is true that in the West, cultural norms of purchasing meat after the butchering process, and only eating a few types of animals, has reduced the risk of being infected by viruses endemic to the animal species we consume.
And while wet markets no doubt have room to improve in terms of hygiene standards, it would be naïve for Australia to pass the buck on future infection control to China when we are no strangers to facilitating zoonosis ourselves.
For example, earlier this month the Nepean Blue Mountains local health district in NSW told doctors to be aware of cases of “parrot fever” or psittacosis, a rare bacterial infection acquired by exposure to infected birds or their droppings.
Understandably, the three patients diagnosed with the condition were mistaking their mild flu-like illness, which can also develop into severe pneumonia, as symptoms of COVID-19.
But as Australia and some of its allies continue to focus the blame of zoonotic infection on China and its wet markets, the WHO remains steadfast in its call for better regulation rather than jeopardising the livelihoods of those working in these markets and reducing the supply and affordability of food for many people.
The WHO is continuing to work with other United Nations bodies to develop guidance on what the safe operation of wet markets might look like in the future while reducing some of the risks they might pose to global health.