Research suggests Covid-19 on chilled salmon could be infectious for over a week

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  • The non-peer reviewed paper implies refrigerated salmon could be a source of international transmission
  • Two of China's coronavirus outbreaks began in wet markets that centred on seafood
South China Morning Post |
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Scientists in China found that the coronavirus can survive on chilled salmon for up to eight days. Photo: Shutterstock

Chinese researchers have discovered that the coronavirus that causes Covid-19 can survive for a week or more on the surface of fresh, chilled salmon, raising concerns it could be a source of international transmission.

The experiment discovered that the virus remained infectious for eight days after being kept at a temperature of 4 degrees Celsius. The experiment also found that Sars-CoV-2, the official name for the virus, remained infectious on the salmon for two days at 25 degrees, which the researchers called “regular room temperature”. 

Salmon is typically kept at 4 degrees in markets, restaurants and during transport, extending the virus’s lifespan by six days. High-quality salmon can be moved across the world in a matter of days. For instance, Chile’s fishing authority said last year that salmon could reach Shanghai in two-and-a-half days. 

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“Under such conditions, (coronavirus) contaminated fish from one country can be easily transported to another country within one week, thus serving as one of the sources for international transmission,” said the Chinese scientists, led by Dr Dai Manman, in a non-peer-reviewed paper published in biorxiv.org on Monday. 

“This calls for strict inspection or detection of (the coronavirus) as a critical new protocol in fish importation and exportation before allowing sales.” 

Two of China’s coronavirus outbreaks – the initial outbreak in Wuhan and a later spread in Beijing in June – have both been associated with wet markets that sold seafood. 

China temporarily halted salmon imports in mid-June after the virus was reportedly discovered on salmon chopping boards at Xinfadi market, the centre of the Beijing outbreak. Authorities later ruled out salmon as the source of transmission. 

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The cases in Wuhan and Beijing created “concerns that fish or meat-attached SARS-CoV-2 could be a potential source of Covid-19 transmission,” wrote Dai, associate professor with the South China Agricultural University in Guangzhou.

The researchers bought the fish from a shop in Guangzhou, cut the meat into small cubes and treated them with a solution containing the viral particles before storing the cubes at different temperatures. Each day a sample was taken out for a test to see if the virus could infect normal cells.

Experts believe the lower the temperature, the longer the virus could survive, but whether these products remained infectious was unknown. The salmon experiment suggests they are.

Chinese Customs has caught coronavirus in numerous imported food products ranging from shrimp to chicken wings. All these products were transported in temperatures far below freezing.

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