A recent study has provided crucial insights into the origins of SARS-CoV-2, the virus behind COVID-19. Researchers have linked the virus to wildlife species sold at the Huanan seafood market in Wuhan, China. The analysis, based on metagenomic RNA data, reveals the presence of virus-linked animals, offering evidence that the pandemic likely began at this location.
The study, published in Cell, examined RNA samples collected shortly after the market’s closure in early 2020. This research supports growing evidence that the virus jumped from animals to humans, sparking the global pandemic.
Though the market closed due to early outbreaks, the Chinese Center for Disease Control and Prevention (CDC) collected environmental samples from areas where animals had been kept. A detailed analysis has now identified specific animals, such as raccoon dogs and civets, as potential carriers of the virus.
EARLY SIGNS IN WUHAN AND LINGERING THEORIES
COVID-19 was first detected in Wuhan, the capital of China’s Hubei province, in late 2019. The city also hosts the Wuhan Institute of Virology (WIV), where scientists studied corona viruses, leading to speculation about a possible lab origin of the virus. However, current research strongly indicates that SARS-CoV-2 is of natural origin and was not engineered in a lab.
Despite suspicions, virologists maintain that the virus most likely spread from animals sold at the Huanan market, where conditions were conducive to zoonotic spill over – the transmission of a virus from animals to humans.
NEW ANALYSIS OFFERS VITAL CLUES
To further investigate COVID-19’s origins, an international team of researchers analyzed metagenomic data gathered by the Chinese CDC in early 2020. The study’s senior author, Florence Débarre, an evolutionary biologist at the French National Centre for Scientific Research (CNRS), called this dataset “one of the most important” regarding the pandemic’s origin.
Investigators collected over 800 samples from the market, swabbing surfaces in animal stalls, cages, carts, and drainage areas. These samples were subjected to metatranscriptomic sequencing, revealing RNA sequences from various organisms, including humans and animals, as well as the virus itself.
TRACING ANIMALS AND VIRUS IN THE MARKET
Using mitochondrial genome genotyping, the researchers identified animal species present at the market before it closed. Evidence of SARS-CoV-2 was found in animal stalls that housed species such as raccoon dogs and civets. Some of these stalls contained both animal genetic material and virus RNA on the same swab, suggesting that these animals were possible intermediate hosts.
“We are seeing the DNA and RNA ghosts of these animals,” said Débarre. “This is what you would expect in a scenario where infected animals were present in the market.”
Although the animals had been removed by the time samples were taken, the presence of their genetic material in areas contaminated with SARS-CoV-2 adds a layer of evidence to the theory of animal-to-human transmission.
A LIKELY ORIGIN OF THE PANDEMIC
The study also conducted an evolutionary analysis of early viral genomes, aiming to trace potential predecessors of SARS-CoV-2. The findings support the hypothesis that the virus emerged in the market and that few, if any, infections occurred before market-related outbreaks.
The market-linked viral sequences reflect the main genetic diversity of SARS-CoV-2 from the early days of the pandemic. “We show that the sequences linked to the market are consistent with a market emergence,” said Débarre.
POTENTIAL ANIMAL HOSTS IDENTIFIED
Based on their findings, the researchers created a list of animals that were most likely involved in the virus’s transmission. The common raccoon dog (Nyctereutes procyonoides) was the most genetically abundant species identified in the samples. Masked palm civets (Paguma larvata) were also detected in stalls containing SARS-CoV-2 RNA.
Both species were previously linked to the SARS outbreak in 2002, and raccoon dogs are known to be highly susceptible to SARS-CoV-2. These findings point to a potential repeat of a similar transmission process involving corona viruses and wildlife.
THE ZOONOTIC THREAT OF WILDLIFE MARKETS
The presence of these animals, combined with dense human populations in cities like Wuhan, creates a perfect environment for zoonotic diseases to spread. Ecologist Michael Worobey of the University of Arizona stated, “This is the most risky thing we can do – take wild animals that are teeming with viruses and bring them into contact with humans in highly populated cities.”
EVIDENCE CONTINUES TO BUILD
While the new study doesn’t definitively prove that animals at the market were infected with SARS-CoV-2, it contributes important clues about the pandemic’s origin. It also reinforces the idea that the Huanan seafood market was likely the starting point for the virus’s spread to humans.
According to Kristian Andersen, an evolutionary biologist at the Scripps Research Institute, this research adds to the growing body of evidence pointing to a zoonotic origin. “All the evidence points to the same scenario: infected animals were introduced into the market, which sparked the pandemic,” said Andersen.
LESSONS FOR FUTURE PANDEMICS
The implications of this study go beyond understanding the past. It highlights the dangers of wildlife markets and the need for stronger measures to prevent zoonotic diseases from emerging again.
Despite heightened awareness of the risks posed by zoonotic spillovers, little action has been taken to reduce the chances of similar pandemics occurring in the future. Worobey stressed that, while lab safety has improved, more needs to be done to address the root causes of such outbreaks.
A STEP TOWARD PREVENTING FUTURE PANDEMICS
This study provides a roadmap for future pandemic prevention, emphasizing the importance of regulating wildlife trade and improving monitoring of animal-borne viruses. By identifying which species are most likely to harbour dangerous pathogens, researchers can help reduce the chances of zoonotic spillovers and future pandemics.
The study’s findings underscore the need for a global effort to regulate the trade of wild animals and improve bio security measures.
