More than a year after a “mysterious pneumonia” that plagued employees at a seafood market in China, scientists are still gathering clues as to where SARS-CoV-2 – the virus that causes COVID-19 – originated.
“It’s critical to understand where this virus comes from so we can understand how we can stop future outbreaks,” said Anne Rimoin, an epidemiologist at Infectious Diseases at UCLA.
The investigation into the origin of the virus is crucial for public health and scientific reasons, but it has also fueled tensions among world powers, particularly between the United States and China, whose leaders have accused each other of lack of transparency and xenophobia during the pandemic.
“It’s not about finger pointing – it’s just about understanding it, so we know how to do better in the future,” Rimoin said.
Therefore, on January 14, 2021, the World Health Organization deployed a group of 17 international experts to Wuhan to work with Chinese scientists on an in-depth investigation into the origin of the virus.
Scientists have long said that SARS-CoV-2 has zoonotic origin, meaning that it probably jumped from animals to humans when humans came in contact with an animal infected with the virus. The contact may include handling the infected animal, eating it or preparing the animal according to the market, according to Rimoin.
However, experts did not know exactly how the virus ended up in humans and that it could come to a definite conclusion about the origin of SARS-CoV-2, which would take years. They also do not know where or when the virus first entered humans, and several studies suggest that it occurred elsewhere in the world – perhaps at low levels – before the major outbreak in Wuhan, China.
“You are trying to reconstruct events from a year and a half ago with incomplete sampling and data,” said dr. W. Ian Lipkin, director of Columbia University’s Center for Infection and Immunity, told ABC News. “We may never know exactly what happened.”
If there is an idea of previous investigations into infectious diseases, the origin of the virus may remain a secret. The best comparison is the SARS outbreak in 2003, which was caused by a close cousin of the virus that causes COVID-19 and was eventually traced back to a single population of bats.
But that search lasted more than five years. “I think they were quite happy,” said Vincent Racaniello, a professor of microbiology and immunology at the College of Physicians and Surgeons at Columbia University. “We still have not found the source of Ebola virus outbreaks after many years of investigation,” he added. “It’s not easy.”
The joint WTO-China report is seen as a first step in the likely years-long investigation that unveiled its findings last week. But the report itself is caught up in controversy. Following the release, the United States and 13 other countries in a joint statement expressed concern about the report, arguing that the international inquiry was “significantly delayed and lacked access to complete, original data and samples.”
But many experts believe that the report, although imperfect, is an important first step.
The investigators investigated four main theories on how the virus spilled over to humans, ranking those who rank the theories in order of probability, from ‘most likely’ to ‘extremely unlikely’.
The intermediate host theory: This theory suggests that the virus was transmitted from an original animal host to an intermediate host, such as mink, pangolins, rabbits, raccoon dogs, domestic cats, rivets or ferrets, and then humans were directly infected by live contact with the second animal. .
Conclusion of WHO-China investigation: “probably to most likely”
The zoonotic distribution theory: The zoonotic run-out theory suggests that SARS-CoV-2 was transmitted directly to humans from an animal, probably a bat. This transmission could have taken place through farming, hunting or other close contact between humans and animals.
Conclusion of WHO-China investigation: “possible to probable”
The frozen food chain theory: The ‘cold chain’ theory suggests that SARS-CoV-2 could be transmitted from animals to humans through contaminated frozen food. A frozen food product contaminated with animal waste containing SARS-CoV-2 could have transmitted the virus to humans without any direct live human-animal contact.
Conclusion of WHO-China investigation: “possible”
Controversial laboratory leak theory is ‘extremely unlikely’
As part of the investigation, scientists returned to the Huanan seafood market associated with the first known group of cases in Wuhan. They also visited Hubei Provincial Hospital for Integrated Chinese and Western Medicine, where some of the first COVID-19 cases were treated, and looked at data for viral sequence. The viral sequence showed that different small variants of SARS-CoV-2 spread in Wuhan in December 2020.
“This again suggests that the virus may have been circulating a little longer than people realized,” said Dominic Dwyer, an epidemiologist and member of the WHO investigation team.
Viral sequence also showed that the Huanan market was probably not the primary source of the outbreak. While many early cases have been linked to the market, a similar number of cases have been associated with other markets or not at all, the WTO-China report found.
“The market was certainly an amplifier, but probably not the original source of the whole outbreak,” Dwyer said.
Preliminary genomic sequences showed that the virus originated naturally and that the WHO-China team considered the laboratory leech theory “extremely unlikely”.
But dr. Tedros Adhanom Ghebreyesus, the director general of the WHO, said he did not think the team’s assessment of the theory was comprehensive enough.
Further data and studies will be needed to draw more robust conclusions, Tedros said at a news conference on the report’s findings.
“Science can not exclude such things,” said Peter Daszak, a zoologist and member of the WHO’s research team, about the laboratory theory. “You can only show really positive findings, but you can not be negative. But what we found is that the escape from the laboratory was extremely unlikely.
The most likely route, according to the report, was the first theory that the virus transmitted from a bat to an intermediary and then to humans. According to Daszak, the following steps for investigation may include detecting the first cases of the virus; investigation of market providers for unusual increases in antibodies; and the exploration of sites with concentrations of animals we know is susceptible to SARS-CoV-2.
Rimoin hopes the pandemic has shown that disease surveillance is the key to preventing, and not just responding to, future outbreaks. ‘As population growth and climate change push people further into animal habitats, we will see more viruses jumping from animals to humans, and we will see more events that prevent disease,’ ‘Rimoin said.
“An infection anywhere is possibly an infection everywhere,” she said.
ABC News, Sasha Pezenik, Sony Salzman and Eric Silberman contributed to this report.
Eric Silberman, MD, a family physician in internal medicine at Northwestern Memorial Hospital, is contributing to the ABC News Medical Unit.