The 5 mysteries that persist about the origin of the pandemic

Following a month-long fact-finding mission to China, a World Health Organization (WHO) team investigating the origins of the COVID-19 pandemic concluded that the virus probably originates from bats and it passed to the people through an intermediary animal. However, questions remain about when, where and how the coronavirus first infected people. The magazine Nature collected what are the 5 main mysteries to answer.

1- Was the virus circulating in the city of Wuhan before the recording of the first confirmed cases?

To trace the origin of the virus, it is crucial to determine exactly when the first cases occurred in humans. The WHO team has established that the first known person with COVID-19 was an office worker in Wuhan with no recent travel history, who started showing symptoms on December 8, 2019, according to Peter Ben Embarek, a WHO food safety scientist in Geneva, Switzerland, who conducted the investigation. But the virus was probably spreading in the city before. Because he was well established at the end of December.

However, evidence of a previous spread has been elusive. Chinese researchers conducted an in-depth study of patient reports from Wuhan hospitals conducted between October and December 2019, and they identified less than 100 people who had symptoms of COVID-19. They then tested the blood of 67 of these people for antibodies generated by a previous infection with SARS-CoV-2, but found none. This suggests that there was not a large cluster of infections before December, nor an unusual spike in deaths in the surrounding province of Hubei.

However, scientist Ben Embarek says the analysis should be repeated using less restrictive symptom criteria, to ensure researchers detect all possible cases of COVID-19. Chinese scientists are also expected to look for evidence of past infections in 200,000 archived samples that are currently kept at the Wuhan Blood Center and other parts of China. said Dominic Dwyer, team member and medical virologist at New South Wales Health Pathology in Sydney, Australia. This would show whether the virus was spreading in the general population of China – not just among people attending health centers – before December 2019.

Some scientists not involved in WHO research have already analyzed blood bank samples taken up to a year before the pandemic in Guangzhou, southern China. Some of the samples tested positive for anti-SARS-CoV-2 antibodies, but Ian Lipkin, an infectious disease researcher at Columbia University in New York who worked on the analysis, says the test was not specific enough. to say for sure that the antibodies were not caused by infection with other viruses. “There’s a lot of lab work to be done that hasn’t been done,” says Lipkin, who He wants to know if there are autopsy samples from before December 2019 that could be studied for traces of viral genetic material.

2- Did the virus spread to people outside of China before December 2019?

This question is also essential for establishing the timeline of the first cases of COVID-19. European researchers have previously reported finding anti-SARS-CoV-2 antibodies in samples taken from blood banks in November 2019. Ben Embarek clarified that this does not necessarily suggest that the virus originated in Europe, but supports the idea that it was spreading in Wuhan before the first known cases.

“Wuhan at that time was a very well connected international city with daily direct flights to the whole planet. So, if it was circulating in Wuhan, it could easily have been transported to other parts of the world via travelers, and circulated again, undetected, to different regions. “Embarek said. Nonetheless, he recommends that blood samples from Europe be tested again to confirm if they were cases of COVID-19. Some of them, from Italy and France, are already being tested again.

3- What was the role of the Huanan market?

The intermediate animal that transmitted the virus from bats to humans has yet to be identified, but researchers believe it can be a wild species sold for food in markets which usually sell live animals. At the start of the pandemic, researchers focused on the Huanan seafood market in Wuhan as it sold fresh and frozen animals and many of the early infections occurred in people who had visited it. But the trail cooled when other early cases were discovered that weren’t associated with the market. Viral material has been identified in sewer and wastewater from the market, but none has been found in animal carcasses.

Yet the market is the only place where large numbers of people infected at the start of the epidemic were exposed to meat and animals. It is important to determine how the virus came to market and whether it was an animal, says Hung Nguyen-Viet, WHO team member, Researcher in environment and food security at the International Livestock Research Institute in Nairobi.

Nguyen-Viet said the team had identified 10 stalls selling wild or farm animals that may have brought the virus to market from farms in southern China. Some wild animals sold for meat, such as badger rabbits and ferrets, are susceptible to SARS-CoV-2 or the related virus that causes severe acute respiratory syndrome (SARS).

Meanwhile, Peter Daszak, a member of the WHO team and chairman of the New York-based nonprofit research organization Ecohealth Alliance, said farms should be surveyed to see if there are infections in or among animals.. He also wants to know which animals were sold in other markets in Wuhan. When the team interviewed the first person known to have COVID-19, they mentioned that their parents had visited a local community live animal market, Daszak says.

4- Did frozen wild animal meat play a role in the early spread of the virus?

The WHO team concluded that the virus was most likely transmitted from live animals to humans, but Ben Embarek says it is possible that the virus entered the Huanan market via infected frozen wild animals. from farms in southern China, which then triggered an epidemic. Daszak wonders if frozen ferrets sold in the market could carry the virus. “They were skinned corpses in the market, not just cubes of meat in plastic wrap,” he said.

Although Chinese researchers have also isolated viral RNA from packaging of imported frozen fish, scientist Ben Embarek said the WHO team concluded that the goods were not likely to be the first route of arrival of the virus in Wuhan. Meanwhile, Lipkin says that there is no evidence that the virus entered the market through infected frozen wild animals. It could easily have come from infected people handling wild animals, he says.

5 – Was the virus circulating in animals in China before the pandemic?

To determine which animal transmitted the virus to humans, researchers need to find evidence of the virus in that species. Chinese researchers analyzed some 30,000 wild, farmed and domestic animals in 2019 and 2020, but They found no evidence of past or active SARS-CoV-2 infection, except in some cats in Wuhan in March 2020.

However, Ben Embarek says that work was not representative of China’s general animal population and that many other animals need to be tested for traces of infection, especially on wildlife farms. “The amount of testing that has been done is not enough to say, in any way, that wild animal farms did not carry the virus,” Daszak said.

The explosive way the Wuhan outbreak occurred in December suggests the virus was likely introduced once, through the wildlife trade.Note Daszak. He says future testing should focus on wild animals on the farm.

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