Recent investigations on specimens from Wuhan's livestock market reinforce its identification as a significant spreader's hub for the initial Covid-19 outbreak.
The regions with the highest concentrations of SARS-CoV2 samples contain various species, such as raccoon dog, hoary bamboo rat, dog, European rabbit, Amur hedgehog, Malayan porcupine, Reeves’s muntjac, Himalayan marmot, and masked palm civet.
Recent findings strengthen the suggestion that the SARS-CoV2 virus transitioned from animals to humans and that the market served as an essential hub for its initial dispersal.
Researchers were able to identify the animals at the market by employing metagenomic sequencing, which involves analyzing all the genetic material in a sample to discern its origin.
The research, which was released Thursday in the journal Cell, does not definitively establish that the animals were infected by the virus, but their genetic material was found closely linked to the virus, sometimes even on the same swab. Thus, the possibility that the animals were infected at the market is quite high.
Among the market animals, rabbits, dogs, and raccoon dogs are known to be susceptible to Covid-19 infections, and raccoon dogs have been shown to transmit the infection, making them a strong candidate for being the animals that initially transferred the virus to humans.
Examining the age of viruses
The international research group responsible for the study also utilized the genetic material from samples gathered at the market to conduct an evolutionary analysis. This method allows them to estimate the viral origin and its closest genetic relative by estimating the virus's age.
Dr. Kristian Andersen, the study's senior author and director of infectious disease genomics at Scripps Translational Research Institute in La Jolla, California, said, "It's basically carbon dating viruses."
By determining the rate at which Covid-19's virus mutates, or changes, it is possible to estimate the virus's age. The virus that causes Covid-19 acquires about two genetic mutations each month.
The team's analysis suggests that the virus that ignited the pandemic emerged around mid-November to mid-December 2019. The virus found at the market also emerged at the same time, suggesting they are one and the same.
If the virus originated elsewhere first and then traveled to the market where its spread was amplified, as suggested by the lab leak theory, the timing of the market-found virus's emergence would have been different from the pandemic virus's. The pandemic virus would have an earlier birthdate.
Other evidence corroborates this theory. Approximately one-third of the first 174 individuals diagnosed with Covid-19 had ties to the market, and many others living near the market but without a direct connection still fell under the city of 12 million people.
When Andersen first observed the closeness of this cluster, he was astonished. "I was flabbergasted," he said.
Upon analyzing the results of the hundreds of swabs taken at the market in January 2020, Andersen was astounded by the concentration of environmental positivity within the market. "My brain was literally blown," he said.
Another compelling indicator that the market may have been the ground zero for the pandemic is the presence of both lineages of the virus that circulated during the pandemic's early stages — the "A" lineage and the "B" lineage — on the swabs gathered at the market.
Accumulating evidence of animal origin
Andersen emphasized that scientists have never been in possession of such comprehensive data at this degree of detail for any prior pandemic.
The findings closely align with a similar analysis performed by Chinese scientists that was published in the journal Nature in 2023. The data used to conduct the analysis was briefly the subject of international intrigue when it was quietly posted on GISAID in March 2023, a site for researchers to exchange viral genetic sequences.
Dr. Florence Debarre, a researcher at the French National Centre for Scientific Research (CNRS), discovered the data in 2023 and notified other scientists. She is also a co-author of the new study with Andersen.
"What this adds is a greater weight of evidence," Debarre said in an interview about the new study. "Because as data keep accumulating, all the results still go in the same direction, which is an origin linked to wildlife trade in the Huanan market."
This study is the latest in a series of important scientific papers by the same research group, which have been published in major journals, supporting the theory that the Covid-19 pandemic began with an animal origin.
Andersen recognizes that many people will dismiss the findings of the new study due to his involvement in the research. He insists that he couldn't care less.
"They will just look at the author list on the paper and say, ‘Oh, yeah, we can’t trust any of this,’ right? So we don’t even need to read the paper," Andersen said.
Andersen has been a prominent figure leading an international team of scientists who have been investigating the scientific evidence collected during the early stages of the pandemic in order to understand how the global public health crisis began.
Andersen has faced intense scrutiny due to his changing stance, originally believing that SARS-CoV2 was developed in a lab in Wuhan, which manipulated similar viruses, but later publishing a scientific paper supporting the theory that the virus was likely transmitted from animals to humans — an event referred to as a spillover.
Animal spillovers are the usual origin point for pandemics.
Supporters of the lab leak hypothesis suggest that Andersen was influenced by top scientists from the National Institutes of Health to alter his perspective.
Andersen disputes this claim, stating that he merely adapted his theory in response to evidence contradicting his initial beliefs, as is common practice among scientists.
Debarre admits that she, too, initially believed that the virus originated from a lab.
"A lab origin is a plausible scenario. It's a valid possibility that warranted serious consideration, which we indeed considered," Debarre said.
Andersen, she notes, is widely recognized as the initial advocate of the lab leak theory.
"We were all open to the possibility of a lab leak, but as scientists, we follow the data. And so far, all the available data point towards a spillover event from animals, likely occurring in the Huanan market," Debarre concluded.
Lessons from past pandemics
Determining the origin of SARS-CoV2 is critical, not just for understanding the Covid-19 outbreak, but also for anticipating future pandemics.
Andersen asserts that significant efforts have been taken post-pandemic to enhance lab safety and minimize the probability of releasing hazardous viruses. However, he emphasizes that less focus has been given to the uncontrolled trade of wild and domesticated animals, a practice that continues to pose significant risks.
Subscribe to CNN Health's weekly newsletter
- Subscribe here to receive The Results Are In with Dr. Sanjay Gupta every Friday from the CNN Health team.
"How frequently has the unregulated wildlife trade, a $50+ billion annual industry in China, been discussed?" Andersen questioned.
Andersen also highlighted the presence of the H9N2 flu virus – another potential emerging virus – in the Huanan market samples.
"It serves as a chilling reminder that SARS-CoV2 wasn't unique in that regard. It was just a virus that found itself in the right place at the right time," Andersen concluded.
The same scenario that unfolded in Wuhan in 2019 might be occurring now with the H5N1 bird flu virus in the United States on poultry and dairy farms. As long as the virus is spreading, Andersen said, "it's a matter of chance."
Although Andersen agrees that there should be stricter oversight of lab research on viruses, he believes more attention should be devoted to animal markets.
"And the real threat looming before us is the unregulated wildlife trade, which is a subject that doesn't seem to be getting the attention it deserves," Andersen asserted.
The findings from the genetic material analysis suggest that the Covid-19 virus, which causes significant health concerns, could have originated from animals sold at the market, specifically raccoon dogs, rabbits, and dogs, which are known to be susceptible to Covid-19 infections.
Following the outbreak, Dr. Kristian Andersen emphasized the importance of understanding the origin of viruses like SARS-CoV2, not only for addressing the current pandemic but also for anticipating future health threats, especially in the context of unregulated wildlife trade, which poses significant risks.
