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How is African swine fever linked to COVID-19? Tanes Ngamsom/Getty Images
  • Multiple studies indicate that COVID-19 is a zoonotic disease, transferred from animals to humans.
  • A recent paper supports the argument that the pandemic is more likely to have begun in a marketplace than in a laboratory.
  • Interestingly, the authors also discuss whether African swine fever might have played a role in the spillover event that led to the COVID-19 pandemic.

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Researchers at the University of Glasgow in the United Kingdom recently took a fresh look at how the COVID-19 pandemic arose in China.

Their findings confirm earlier work pointing to an “intermediate animal host” that may have introduced SARS-CoV-2 to humans.

The paper also discusses the possibility that an African swine fever outbreak helped create a situation that gave pathogens more opportunities to jump from animals to humans.

Spyros Lytras is a graduate student at the University of Glasgow Centre for Virus Research. He and his co-authors published their perspective piece in the journal Science.

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The current article kicks off in 2002, discussing severe acute respiratory syndrome coronavirus (SARS-CoV), which emerged in Foshan, Guangdong Province, China, and spread to 29 other countries.

More than 8,000 people contracted SARS-CoV before public health measures halted its progress in 2003.

Experts tied the virus’ origin to live market animals.

In 2005, researchers discovered that horseshoe bats in China were harboring SARS-related coronaviruses (SARSr-CoVs).

They speculated “that a [SARSr-CoV] circulating in horseshoe bats seeded the progenitor of SARS-CoV in an intermediate animal host.”

Scientists looked at badgers, civet cats, and raccoon dogs as possible carriers of the virus. They pinpointed civet cats as the most likely transmitters.

Virologists hypothesized that a civet cat could have been exposed to a SARSr-CoV before capture. An alternative theory suggests a captive civet cat may have contracted the virus from bats foraging in markets.

In 2019, SARS-CoV-2, the virus that causes COVID-19, appeared in Wuhan city, China. Some implicated the Wuhan Institute of Virology as the source of the pandemic.

Indeed, Wuhan is over 930 miles (1,500 kilometers) away from Yunnan Province, the nearest known site of naturally occurring SARSr-CoV collected from horseshoe bats.

Further, those Yunnan-collected viruses were “highly divergent from the SARS-CoV-2 progenitor.”

In their paper, the authors cast doubt on the focus on bat colonies in Yunnan. They explain that the geographical range of horseshoe bats is wide — from East to West China and beyond. They also explain that further sampling has identified other coronaviruses that are genetically close to SARS-CoV-2 circulating in horseshoe bats.

The first SARS-CoV-2 cases detected in late 2019 had links to wet markets in Wuhan.

November and December 2019 also saw “multiple animal-market-associated spillover events.” The paper explains that “[t]he emergence of SARS-CoV-2 has properties that are consistent with a natural spillover.”

Among several live animal species sold in Wuhan markets, raccoon dogs, civet cats, foxes, and minks are susceptible to SARS-related viruses.

Lytras and his colleagues conclude that the COVID-19 pandemic stems from human contact with live animals that carried the virus.

The paper also conjectures that changes to China’s meat supply may have played a role in spreading SARS-CoV-2.

African swine fever is a hemorrhagic fever that is often fatal in pigs but does not harm humans. In 2018, a significant outbreak of African swine fever led to a cull of 150 million pigs. This led to a shortage of pork products and soaring prices the following year.

Although the production and sale of meat from other farmed animals, such as cows and chickens, increased, it was not enough to make up for the shortage in pork.

The authors of the new article theorize that as a result, “food consumers and producers may have resorted to alternative meats, including farmed or captured wildlife, especially in Southern China where wildlife is traditionally consumed.”

This perspective states: “The resulting increased trade of susceptible farmed animals and wildlife could have brought humans into more frequent contact with meat products and animals infected with zoonotic pathogens, including SARSr-CoVs.”

At the same time, in an effort to reduce live pig transportation, the Chinese government introduced financial incentives to carry frozen pork. This, the authors of the paper argue, may have encouraged the transport of other species, which are susceptible to SARSr-CoV infection.

The exact animal source of SARS-CoV-2, though, is still unknown.

Dr. Jonathan Stoye is a renowned virologist and Senior Group Leader at the Francis Crick Institute in the U.K. In an interview with Medical News Today, Dr. Stoye remarked that this paper provides “an excellent summary of the devices supporting the case that the introduction of [COVID-19] to humans involved an intermediate host.”

The virologist, who was not involved with this paper, noted that the authors’ conclusion was similar to the WHO-convened study published in February 2021. As such, he saw “nothing original” in this work.

Dr. Stoye cautioned that this perspective “doesn’t prove a transfer from bats to humans.”

He was, however, intrigued by the author’s theory that a pork shortage might have provided fertile ground for a spillover event; this possibility has not received much attention.

Scientists expect to see new SARS-CoV variants emerge. The University of Glasgow researchers say that the discovery of these variants and other SARS-related viruses underscores the importance of “monitoring coronavirus diversity.”

In March 2020, the World Health Organization (WHO) issued recommendations to reduce the animal-to-human transmission of SARS-CoV-2 in live markets.

These guidelines include general hygiene methods and avoiding the consumption of raw or undercooked animal products from such markets.

The WHO also asks veterinarians to report unusual incidents involving market animals.

The authors worry that now humans are the “dominant SARS-CoV-2 host species,” we could be transmitting coronaviruses back to animals. This process of reverse zoonosis seems to have occurred among white-tailed deer in the United States.

However, in his interview, Dr. Stoye predicted a “gradual lessening” of the spread of SARS-CoV-2. This appears to be happening among areas with higher vaccinations.

As with many virologists and immunologists, he expects that SARS-CoV-2 and its variants will meet the same fate as the first SARS-CoV — gradually posing less danger over time.

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