July 27, 2022 – Many scientists and public health experts have long said that coronavirus that caused a global crisis pandemic from a market in Wuhan, China. Now, two new studies bolster that argument.
The initial spread of the virus was a punch, according to the studies. Twice the virus jumped from animals to humans. Viral genetics and epidemic modeling in one study revealed two strains released within weeks of each other in November and December 2019.
“Now I realize that it sounds like I just said a once-in-a-generation event has happened twice in a row, and pandemics are indeed rare,” said Joel O. Wertheim, PhD. , during a briefing sponsored by the American Association for the Advancement of Science.
A unique storm of factors must have been present for epidemic exploding into a pandemic: animals carrying a virus that could spread to humans, close human contact with these animals, and a city large enough for the infection to take off before it can be contained are examples.
Unfortunately for us humans, this coronavirus – SARS-CoV-2 – is a “generalist virus” capable of infecting many animals, including humans.
“Once all the conditions are in place…the barriers to fallout have been lowered,” said Wertheim, a genetic and molecular network researcher at the University of California, San Diego. In fact, beyond the two strains of the virus that took hold, there were probably up to two dozen times when people got the virus but didn’t spread it very far, and it got off.
Overall, the odds were against the virus – 78% of the time the “introduction” into humans was likely to go away, the study showed.
The research found that the COVID-19 pandemic started small.
“Our model shows that there were probably only a few dozen infections and only several hospitalizations due to COVID-19 in early December,” said Jonathan Pekar, a graduate student working with Wertheim.
In Wuhan at the end of 2019, Pekar said, there was not a single positive coronavirus sample among thousands of samples from healthy blood donors tested between September and December. Likewise, not a single blood sample from patients hospitalized with influenza-like illness from October to December 2019 tested positive for SARS-CoV-2.
Mapping the epidemic
A second study published in the journal Science mapped the first cases of COVID-19. The effort showed a tight group around the wholesale seafood market in Wuhan, a city of 11 million.
When the researchers tried other scenarios — modeling outbreaks in other parts of the city — the model didn’t hold. Again, the Wuhan market appeared to be ground zero for the onset of the pandemic.
Michael Worobey, PhD, and his colleagues used data from Chinese scientists and the World Health Organization for the study.
“There was this extraordinary pattern where the highest density of cases was both extremely close and very centered in this market,” said Worobey, head of ecology and evolutionary biology at the University of Arizona. in Tucson.
The highest density of cases, in an 8,000 square kilometer city, was a “very, very small area of about a third of a square kilometer,” he said.
The pattern of the outbreak showed that the Wuhan market “was right in the middle”.
So if it started with infected workers at the market, how did it spread from there? It is likely that the virus entered the community when market vendors visited local shops, infecting people in those shops. Then local community members unrelated to the market started catching the virus, Worobey said.
Investigators also identified the market stalls most likely to be involved, a sort of internal clustering. “This grouping is very, very specific to the parts of the market where … they were selling wild animals, including, for example, raccoon dogs and other animals that we know are susceptible to SARS infection. -CoV-2,” said Kristian Andersen, PhD, director of infectious disease genomics at the Scripps Research Institute in La Jolla, Calif.
What remains unknown is which animal or animals carried the virus, although the raccoon dog – a fox-like animal native to parts of Asia – remains central to most theories. Additionally, many farms supplying animals to the market have since been closed, making it difficult for researchers to determine exactly where the infected animals came from.
“We don’t necessarily know, but raccoon dogs were sold in this market up until the start of the pandemic,” Andersen said.
Don’t rule out other theories
People who believe SARS-CoV-2 was released from a lab in China first included Worobey himself. “In the past, I’ve been much more open to the idea of a lab leak,” he said. “And published this in a letter in Science” in November 2021.
The letter was “much more influential than I thought it would be in a way that I think turned out to be quite damaging,” he said. As new evidence emerged since then, Worobey said he came to the Wuhan market source theory.
Andersen agreed that he was more open to the lab leak theory at first. “I myself was pretty convinced of the lab leak until we looked at it very carefully and looked at it more closely,” he said. New evidence convinced him “that in fact the data points to this particular market”.
“Have we disproved the lab leak theory? No,” Anderson said. “Will we ever be able to do this? No. But the origin scenario of the Wuhan market is more plausible. “I would say that these two papers combined present the strongest evidence to date.”
Identifying the source of the outbreak that led to the COVID-19 pandemic is based on science, Andersen said. “What we are trying to understand is the origin of the pandemic. We are not trying to assign blame.”
“Pandemics being pandemics, they affect us all,” Andersen said. “We can’t prevent these kinds of events that led to the COVID-19 pandemic. But what we can hope to do is prevent epidemics from becoming pandemics.”
Rapid data communication and cooperation are needed moving forward, Andersen said. Very strong surveillance systems, including sewage monitoring, could also help monitor SARS-CoV-2 and other pathogens of potential concern in the future.
Healthcare professionals should also be on alert for unusual respiratory infections, the researchers said.
“It’s a goddamn luck that the doctors at Shinwa Hospital were so aware, that they noticed these cases were something unusual in late December,” Worobey said. “It didn’t have to be like this.”