The fish tested positive for antigen. What happened?

◎Science and Technology Daily reporter Chen Xi

Recently, a woman in Shanghai bought a sea bass in a group purchase and later tested the fish for the coronavirus antigen, which turned out to be positive. Previously, a Shanghai resident also posted a video saying that he tested the fish he bought for the coronavirus antigen, which also turned out to be positive.

So why did the fish test positive? Can such fish still be eaten safely? Science and Technology Daily interviewed relevant experts to answer your questions.

The new coronavirus cannot infect fish

"The coronavirus antigen test detects the protein outside the coronavirus membrane. If the test result is positive for fish, it means that the fish may have been contaminated by the coronavirus or a false positive has occurred." Chen Chunqi, a professor at the School of Life Sciences of Hubei University, said in an interview with Science and Technology Daily that if the purchased fish have close contact with people infected with the coronavirus during the fishing, slaughtering, and transportation process, the fish may be contaminated by the coronavirus, but the coronavirus cannot infect fish.

"There are a series of receptors on the cell surface that the new coronavirus can use to attach to cells, and the ACE2 receptor is one of them." Chen Chunqi further explained that fish or other seafood are all low-level non-mammals. Although they also have ACE2 receptors, their structures are very different from those of higher mammals. The new coronavirus and the ACE2 receptors of fish will not bind, so fish cannot be infected, and there are currently no reports of the new coronavirus infecting fish.

At present, there are research experiments that prove that the ACE2 receptors of mice can bind to the mutated novel coronavirus Omicron strain. In addition, there are reports of minks being infected with the novel coronavirus. Earlier, Lu Hongzhou, a member of the National Health Commission's Disease Prevention and Control Expert Committee, made it clear in an interview with CCTV: "After being infected with the novel coronavirus, humans have transmitted the virus to pet dogs and cats. There have been individual reports."

Whether it is a coronavirus antigen test or a nucleic acid test, the test results can only prove that the tested sample has coronavirus extracellular proteins or coronavirus nucleic acids. Many times, coronaviruses have been exposed to the air for a long time, and although the virus surface membrane proteins and internal nucleic acids are still there, they can be detected through antigen and nucleic acid tests, but the virus has been inactivated and has no ability to infect.

There is no evidence of COVID-19 infection through the digestive tract

Based on the evidence currently available, the main ways of infection with the new coronavirus are: direct contact with the respiratory droplets of a person infected with the new coronavirus, or hand contact with objects contaminated by a person infected with the new coronavirus, and then touching the eyes, mouth or nasal mucosa with the contaminated hands.

In order to reduce the risk of the spread of the new coronavirus, Chen Chunqi recommends that the public try not to touch raw fish and raw meat directly with their hands. Before handling such food, they can first disinfect it with alcohol, wash their hands and wear masks before and after handling. At the same time, raw and cooked chopping boards should be separated, food should be cooked thoroughly before consumption, and fruits should be peeled before consumption.

"However, there is no need to panic too much. Even if some viruses are still infectious, as long as you take precautions when handling food, wash it and cook it, you can eat it safely," said Chen Chunqi.

It is understood that at a press conference held by the Joint Prevention and Control Mechanism of the State Council, Feng Luzhao, a researcher at the Chinese Center for Disease Control and Prevention, once stated that no evidence has been found so far that the new coronavirus can be infected through the human digestive tract through eating food, including seafood products.

In fact, the instructions for the antigen test kit clearly state that the test objects are human samples, such as nasal swabs, rather than other samples such as fish gills. "Ordinary residents need to follow the operating procedures in the instructions for the new coronavirus antigen test product for daily testing. Virus pollution is different from environmental pollution. There is no need to test every food one by one like testing environmental samples." Chen Chunqi emphasized.

Source: Science and Technology Daily

Editor: Li Xiaohang (internship)

Review: Julie

Final judge: Wang Yu