An analysis of genetic material taken from hundreds of swabs collected at the Huanan Seafood Wholesale Market in Wuhan, China, has added evidence supporting the market as a site of the early spread of COVID-19.
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Scientists collected hundreds of swabs from surfaces such as walls, floors and drains inside the Huanan Seafood Market in January 2020. These samples were analyzed using metagenomic sequencing, a powerful tool that reads all genetic material in a sample to determine its origin.
The analysis revealed that animals such as raccoon dogs, European rabbits, hoary bamboo rats and masked palm civets were present in the areas of the market where the highest levels of SARS-CoV-2 were detected.
Certain species including raccoon dogs and rabbits are known to be susceptible to COVID-19, with raccoon dogs also being capable of transmitting the virus.
While the analysis didn’t definitively prove that the animals were infected with the virus, the researchers found the DNA of these animals close to or on the same swabs that contained SARS-CoV-2.
The proximity of the animal DNA to viral samples supports the theory that the virus jumped from animals to humans at the market, a process known as zoonotic spillover. This aligns with how many pandemics begin, through animal-to-human transmission in populated areas or markets selling wildlife.
The research team conducted an analysis, which estimated that the virus likely emerged between mid-November and mid-December 2019. This timeline corresponds with the emergence of the pandemic virus indicating that the virus circulating in the Huanan market and the virus that caused the global pandemic were the same.
The genetic material from the market was consistent with the virus strains from the outbreak, suggesting that the market was a central point in the early spread of COVID-19. Had the virus come from elsewhere, such as a laboratory leak, its genetic timeline would likely have been different.
Around one-third of the initial 174 people diagnosed with COVID-19 had direct ties to the Huanan Seafood Market. Even those without direct ties were found to live near the market.
Both lineages of the virus (A and B) that were circulating in the earliest days of the pandemic were found in the swabs taken at the market.
The origins of the Covid-19 virus have been debated with two primary hypotheses dominating discussions, the market animal origin and the laboratory leak theory.
According to a new study published in the journal Cell, scientists have presented substantial evidence that supports the theory of the Covid-19 virus originating from animals sold at the Huanan Seafood Wholesale Market.
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Scientists involved in the study assert that the evidence is beyond reasonable doubt in pointing to infected animals as the source of the pandemic with specific stalls at the market identified as hotspots for both animal and viral genetic material.
Key animals identified in the study include raccoon dogs, civets and bamboo rats. Raccoon dogs are known to catch and transmit Covid-19 in experimental settings.
The researchers describe finding the DNA and RNA ghosts of these animals in the environmental samples collected from various parts of the market. These genetic traces suggest the presence of animals that could have been intermediate hosts for the virus.
Scientists from the US and France used advanced techniques to analyze millions of short fragments of genetic code both DNA and RNA collected from stalls, animal cages and equipment at the market.
The samples used for this study were gathered in January 2020 by Chinese officials providing some of the earliest scientific data on the potential origins of the pandemic.
The analysis identified specific areas in the market where both animal and coronavirus genetic material were found.
Several specific stalls in the market, as well as equipment such as hair/feather removal machines and garbage carts, were found to be contaminated with both animal and viral genetic material.
Many of the animals identified at the market including raccoon dogs and civet cats were also implicated in the original SARS-CoV outbreak in 2002. The presence of these animals at the market strengthens the case that similar wildlife trade conditions led to the zoonotic spillover of SARS-CoV-2.
The research team also detected traces of H9N2, an avian flu virus known to have pandemic potential. This highlights the continued danger posed by the unregulated trade of wildlife in populated urban areas.
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