New research suggests industrial livestock, not wet markets, might be origin of Covid-19

by GRAIN | 30 Mar 2020
Image credit: World Health Organization/Getty

Update June 1, 2020

Since we first published our article on the origins of Covid-19 on 30 March 2020, there is increasing scientific consensus that Covid-19 (Sars-Cov-2) did not originate at the Huanan wet market in Wuhan, as has been widely maintained in the media and even many scientific and governmental publications. On May 23, the director of the Wuhan Institute of Virology publicly stated that the first case of SARS-CoV-2 did not emerge from this market. This was echoed by China’s top epidemiologist, Gao Fu, director of the Chinese Center for Disease Control and Prevention. “It now turns out that the market is one of the victims,” he said.

A study published by Chinese and US scientists on 25 May 2020 also concluded that the virus did not originate from the Huanan market. Like other recent scientific studies that have analysed the initial samples of the virus collected from China, they determined that multiple types of the virus were circulating in China for some time, and that the initial transmission from animals to humans happened prior to the outbreak at the Huanan market. The type that infected people at the Huanan market was a transmissible type that most likely evolved in humans from an initial type that had made the jump from animals. How that initial jump happened is still a mystery.

"This is an animal-origin virus that made the leap, maybe from bats to humans, maybe through… another animal, maybe through livestock. And we don't have the data yet to know where or how," said Colin Carlson, a professor at Georgetown University, in an interview with LiveScience. "I haven't seen anything that makes me feel, as a researcher who studies zoonotic disease, that [the Huanan] market is a likely option.”

Surveys of wild and domestic animals in China and studies of the susceptibility of animals to Covid-19 have not pointed to any obvious candidates that may have acted as the intermediate host between bats and humans, which many scientists believe was a necessary step in the virus’ evolution. In our article, we argued that pigs would be an important species to investigate. Since then, two studies in which pigs were subjected to doses of Sars-Cov-2, found that they were not infected with the disease. It would be important, however, to treat these studies with caution, since they were not conducted with the earlier type of the disease that likely first jumped to humans from animals. Pigs and other species of animals that are intensively farmed in China should continue to be investigated, particularly mink.

We remain convinced that factory farming needs to be treated as one of the most important sources for the emergence of dangerous, new pathogens, including coronaviruses, alongside deforestation and our increasing encroachment into the habitats of bats and other wild animals. These threats are highlighted in a newly published, scientific study that provides a 3-year update on the emergence of new enteric coronaviruses in pigs in China (known broadly as SeACoV). One of these, known as SADS, is referred to in our article and our recent report on African Swine Fever. The authors found that there were several outbreaks of new SeACoV viruses at factory pig farms during that period, and that multiple types were likely involved. They warn that the circulation of these viruses, likely evolving through transmission between bats and pigs (and perhaps rats), is a major risk for the emergence of new pandemic coronaviruses in humans.

Let’s be clear: there is no solid evidence that the origin of the SARS-CoV-2 virus, which is the cause of the current Covid-19 disease pandemic, is an open seafood market in Wuhan that also trades in domestic and wild animals. All that we know is that several early cases of people diagnosed with Covid-19 either worked at this market or shopped there in the days preceding their diagnosis. Many media outlets and pundits have seized on this information to claim that Chinese wet markets and the live trade in domestic and wild animals are to blame for the emergence of the disease1. And some are even calling for a ban on wet markets— which are vital to the livelihoods and food security of millions of small farmers, traders and consumers2.

There is a growing body of evidence that points to a different origin story for Covid-19. We now know that none of the animals tested at the Wuhan seafood market tested positive and about a third of the initial set of reported cases in people in Wuhan from early December 2019 had no connection to the seafood market, including the first reported case 3 4 . And we also now know, thanks to the leak of an official Chinese report to the South China Morning Post that the actual first known case of Covid-19 in Hubei was detected in mid-November, weeks before the cluster of cases connected to the Wuhan seafood market were reported5.

Last week, scientists at the Scripps Research Institute published a genomic sequencing analysis of the SARS-CoV-2 virus in the journal Nature that raises more doubts about the possibility of SARS-CoV-2 having originated at the Wuhan seafood market6.

The scientists conclude that SARS-CoV-2 evolved from natural selection and not genetic engineering in a lab, and they say that this natural selection occurred through two possible scenarios. One is that it evolved into its highly pathogenic form within humans. In this case, a less pathogenic form of the virus would have jumped from an animal to a human host and then would have evolved into its current form through an “extended period” of “undetected human-to-human transmission”. Under this scenario, there is no reason to believe that the Wuhan seafood market had anything to do with the evolution of the disease, even if it is quite possible that an infected person at the market could have transmitted it to others.

The second scenario fits with previous coronavirus outbreaks, in which humans contracted deadly coronaviruses after direct exposure to civets, in the case of SARS, and to camels, in the case of MERS. In this scenario, SARS-CoV-2 would have evolved to its present form in an animal host before transfer to humans. Like many other scientists, the Scripps researchers think that it is most likely that the initial transmission would have occurred from bats to an intermediate animal host, where the virus then evolved to its current form.

The Scripps7 researchers go on to say that the particular genetics of SARS-CoV-2 indicate that “an animal host would probably have to have a high population density (to allow natural selection to proceed efficiently) and an ACE2-encoding gene that is similar to the human ortholog,” which is what the SARS-CoV-2 virus binds to in humans.

So which animals fit this criteria?

Another recently published study identifies the most likely intermediate animal hosts for SARS-CoV-2, based on their presence in Wuhan and their having a human-like ACE2 that enables the binding of SARS-CoV-2. These are the animals the study identified: civets, pigs, pangolins, cats, cows, buffalos, goats, sheep and pigeons8.

Many of the animals on this list are industrially farmed in China, even wild animals like civets and pangolins are intensively farmed for their use in Chinese medicines. Suspicions that wild animal farms may have been behind the Covid-19 outbreak have already led the Chinese government to shut down 20,000 wild animal farms across the country9.

But hardly any attention has been given to some other animals on this list, which more clearly meet the “high population density” criteria. Pigs would be one obvious candidate from this list, for several reasons.

For one, pigs and humans have very similar immune systems, making it easy for viruses to cross between the two species, as happened with the Nipah virus outbreak in Malaysia in 199810. Indeed, just three years before the Covid-19 outbreak began, tens of thousands of pigs in four factory farms in Qingyuan county in Guangdong, less than 100 km from the site where the SARS outbreak originated in 2003, died from an outbreak of a new, lethal coronavirus strain (SADS) that turned out to be 98 percent identical to a coronavirus found in horseshoe bats in a nearby cave11 . Luckily transmission to humans did not occur, but subsequent laboratory tests demonstrated that such transmission could have been possible12.

Hubei Province, where Wuhan is located, is one of the top five largest producers of pigs in China. Over the past decade, small pig farms in the province have been replaced by large factory farms and medium-sized contract operations, where hundreds or thousands of genetically-uniform pigs are confined in high density barns. These industrial farms are the ideal breeding grounds for the evolution of new pathogens13.

Hubei’s factory pig farms are still reeling from a massive outbreak of African swine fever that struck the province and other parts of China just over a year ago, wiping out up to half of the national herd14. In these conditions, it is entirely possible that an outbreak of a new coronavirus among pigs in the province could go unnoticed.

GRAIN and other organisations and scientists have been raising the alarm for over a decade now about how the industrialisation and corporate consolidation of meat production has generated increased risks for the emergence of global pandemics such as Covid-1915. But this reality has been completely ignored by governments and the big meat companies they are beholden to. As noted by evolutionary biologist Rob Wallace16, "Anyone who aims to understand why viruses are becoming more dangerous must investigate the industrial model of agriculture and, more specifically, livestock production. At present, few governments, and few scientists, are prepared to do so.” With the growing carnage from Covid-19, a radical change in direction is more urgent than ever.


1. Therese Shaheen, "The Chinese Wild-Animal Industry and Wet Markets Must Go", National Review, 19 March :

2. “Fresh markets are not to blame for the new corona virus outbreak”, GRAIN, 27 February :

3. Carolyn Kormann, "From Bats to Human Lungs, the Evolution of a Coronavirus", The New Yorker, 27 March :

4. Jon Cohen,"Wuhan seafood market may not be source of novel virus spreading globally", Science Magazine, 26 January :

5. Jeanna Bryner, "1st known case of coronavirus traced back to November in China", Live Science, 14 March :

6. Kristian G. Andersen, Andrew Rambaut, W. Ian Lipkin, Edward C. Holmes & Robert F. Garry, "The proximal origin of SARS-CoV-2", Nature Medicine, 17 March :

7. The Scripps Lab website is here :

8. Ye Qiu,Yuan-Bo Zhao, Qiong Wang, Jin-YanLi, Zhi-Jian Zhou, Ce-Heng Liao, Xing-YiG, "Predicting the angiotensin converting enzyme 2 (ACE2) utilizing capability as the receptor of SARS-CoV-2", Science Direct, 19 March :

9. "Coronavirus closures reveal vast scale of China’s secretive wildlife farm industry", The Guardian, 25 February :

10. Stephen P. Luby, Emily S. Gurley, and M. Jahangir Hossain, "Transmission of human infection with Nipah virus", National Center for Biotechnology Information, 2 November 2009 :

11. "How China’s “Bat Woman” Hunted Down Viruses from SARS to the New Coronavirus", Scientific American, 11 March :

12. Yong-Le Yang, Pan Qin, Bin Wang, Yan Liu, Guo-Han Xu, Lei Peng, Jiyong Zhou, Shu Jeffrey Zhu, Yao-Wei Huang, "Broad Cross-Species Infection of Cultured Cells by Bat HKU2-Related Swine Acute Diarrhea Syndrome Coronavirus and Identification of Its Replication in Murine Dendritic Cells In Vivo Highlight Its Potential for Diverse Interspecies Transmission" Journal of Virology - American Society for Microbiology, 26 November 2019 :

13. "Building a factory farmed future, one pandemic at a time", GRAIN, 3 March :

14. "Building a factory farmed future, one pandemic at a time", GRAIN, 3 March :

15. "Viral times - The politics of emerging global animal diseases", GRAIN, 20 January 2008 :

16. "Capitalist agriculture and Covid-19: A deadly combination", Climate and Capitalism, 11 March :
Author: GRAIN
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