Beijing's largest vegetable wholesale market, Xinfadi market, was shut down Saturday after six new domestic COVID-19 infections and 45 asymptomatic cases were reported and the novel coronavirus was detected on some of the sellers' equipment. 

According to local health officials, the virus was found on a chopping board used by a seller of imported salmon, sparking speculations on whether the fish can spread the virus.

"At present, it is hard to determine the infection source in the market," Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention (CDC), told China's Central Commission for Discipline Inspection.

"We cannot conclude that salmon is the source of infection just because novel coronavirus was detected on a chopping board of a seller," the expert said, adding that the chopping board could be contaminated by infected owner or guests, or other products that carried the virus.

The known hosts for coronavirus are mostly mammals. It's almost impossible for salmon to get infected with COVID-19, Cheng Gong, virologist at Tsinghua University, explained.

"Virus must rely on the viral receptor on the host cell surfaces to infect cells. Without the certain receptor they cannot enter into cells successfully," Cheng added. "All known evidence so far suggest this kind of receptors exist only in mammals, not fish."

A study conducted by University College London also suggests that the novel coronavirus can infect a broad range of mammals, but not fish, birds or reptiles.

"The market has a large flow of people and products, it's difficult to figure out the infection source in a short time," said Wu. "We need to collect samples from different channels for verification… and have all related people and products examined to understand the whole picture."

Can we still eat salmon?

The priority now is to find the source of the coronavirus detected on the chopping board, pointed out Zhong Kai, expert from Chinese Preventive Medicine Association, who advised the public to not eat raw salmon until the results of the investigation are revealed.

No evidence has shown that the novel coronavirus can be transmitted directly through food and drink to humans, said Zhong, as the major transmission routes remain respiratory droplets and close contact.

However, the virus can survive on the surface of an object for hours to a few days, and chilled salmon was transported by air in a low temperature, under which condition "it is theoretically possible for the virus to survive, but the possibility is low," said Zhong.

Compared to eating, the process of purchasing and cooking faces a higher risk. Below are some tips from China's CDC that you can follow to protect yourself from the virus.

For ordinary consumers, Zhong also highlighted the importance of daily protection, such as wearing masks when going out, and washing hands upon entering the house as well as before and after cooking food.

Can fish get infected by coronavirus?

Unlike wild animals like civets and bats which are hosts of coronavirus, fish naturally do not carry coronavirus in their bodies, Wu explained, providing one possibility that the surface of the fish could get contaminated by infected workers.

"And if contaminated fish were shipped to China, Chinese workers could have been infected as they processed the fish, and then that led to further human-to-human transmission," he added. "But this is just one speculation, further confirmation is needed through epidemiological investigation."

Wu called on the authorities to tighten inspection and quarantine on imported and refrigerated products to prevent the risk of further viral transmission.

(Cover via VCG)