Salmon called unlikely virus source

People line up for nucleic acid testing on Sunday at Beijing Youan Hospital, a few kilometers away from Xinfadi wholesale market, which is linked to the latest COVID-19 outbreak. CHEN HAO/FOR CHINA DAILY

Mutated strain that caused outbreak appears to have European origins

Experts said it is extremely unlikely for seafood like salmon to be the carrier of the novel coronavirus, which was found on cutting boards for imported salmon at Beijing's Xinfadi wholesale market, China's new hot spot of COVID-19 infection.

Beijing reported 36 new domestically transmitted cases on Saturday, all having direct or indirect links to Xinfadi market, the biggest wholesale food and vegetable market for the city. The market has been shut down to curb the spread of COVID-19.

Zeng Guang, a senior researcher at the Chinese Center for Disease Control and Prevention, said on Sunday that, based on preliminary analysis of the two early cases, the coronavirus strain in the latest outbreak is different from the ones found in China, and early data suggest it is a mutated variety from Europe.

However, Zeng stressed that people should take this finding with a grain of salt as more testing is being conducted to confirm the origin of virus.

Wu Zunyou, the chief epidemiologist at the CDC, said in a statement on Saturday that fish in their natural habitat cannot catch coronavirus, however, they can be contaminated by workers during capture or transportation.

China imports about 80,000 tons of cooled and frozen salmon each year, according to news site Jiemian.com. Chile, Norway, the Faeroe Islands, Australia and Canada are the main sources of salmon imports.

Wu said that it cannot be concluded that salmon is the source of infection just because novel coronavirus was detected on cutting boards.

"Our seafood products are typically stored and transported in cold containers, thus it is possible for the virus to be preserved for a long time and increase the likelihood of infecting people," he said.

Wu said Beijing's new outbreak could have two possible explanations. The first may be the influx of meat and seafood to the market from all over the country and around the world. Some of it may have been contaminated by workers during processing and transportation, then the virus jumped from produce to people.

The second possibility is person-to-person transmission. "The infected person who brought the virus into the market might be asymptomatic or have very mild symptoms, and the hustle and bustle of the market led to the cluster of new infections," he said.

Wu said there is no need to panic as Beijing has moved swiftly to contain the outbreak. "The know-how accumulated over the last few months, and with the use of advanced technologies like big data, has served us well in our contact tracing and diagnosis initiatives," he said.

"The valuable information we are collecting will be instrumental in Beijing's prevention efforts, and may even reveal new insights into the mysteries of the virus' mode of transmission," he added.

Gao Xiaojun, spokesman for the Beijing Health Commission, said on Saturday that of the 40 environmental samples collected from the market that were later tested to contain the virus, only some came from salmon cutting boards.

A preprint study by the University College London last month found that the novel coronavirus strain can infect humans and a broad range of mammals, but not fish, birds or reptiles.

In April, a study published on the journal Asian Fisheries Science stated that the novel coronavirus is a type of betacoronavirus that can only infect mammals. Moreover, the virus mostly impacts the respiratory system, which most fish do not have. This means the virus is extremely unlikely to infect and multiply in fish. 

Editor: John Li