Can fish be infected with the new coronavirus? Why do we need to do nucleic acid testing?

Recently, fishing officially started in the waters of Xiamen, Fujian. Reporters learned that fishermen in Jimei District have to undergo nucleic acid testing once a day during their operations. When fishermen and their catch come ashore, they will be tested for both people and things. After coming ashore, the fishermen will immediately return to the boat after the nucleic acid collection, catch a few live fish, open their mouths, and let the nucleic acid collectors take samples. In addition to extracting samples from the fish mouths, nucleic acid collectors also carefully use cotton swabs to extract samples from the catch.

It's fine to do nucleic acid tests on humans, but why do fish have to do it? This wave of operations can't help but surprise people. Why do they do this? In fact, this is mainly to prevent smuggling of viruses (but stabbing the throat of fish may not be appropriate), which is equivalent to testing environmental samples. Let's talk about this today.

01. Why do we need to inspect both people and objects?

Do you remember the Sanya epidemic? How did it come about? During the fishing ban period, fishermen went offshore to trade with foreign fishermen and brought the virus back.

Fish caught by foreign fishermen are sold to fishermen on the high seas, and then the fishermen bring the fish back to China for sale. At present, infections are common in some places abroad, so the possibility of fish being infected by the virus is very high. These fish may cause infection when they enter China. This was the case in Sanya at the time. It first appeared among fishermen and then spread to tourists.

So Xiamen does this probably to prevent some people from engaging in illegal smuggling instead of fishing. Buying other people's fish and selling them back home is basically impossible to prevent in the vast ocean. In fact, in July and August, Sanya was the place where fishermen illegally traded overseas, and Tibet may have been from the border.

02. Can fish be infected with the new coronavirus?

It is unlikely that fish can be infected with the coronavirus. PS: There is formal research on this, which is this article:

The article title is:

SARS-CoV-2 spike protein predicted to form stable complexes with host receptor protein orthologues from mammals, but not fish, birds or reptiles

In fact, this is a bioinformatics article. No experiments were conducted, but corresponding calculations and predictions were made using existing data.

Of course, we cannot directly predict whether a certain organism can be infected with the new coronavirus, but through an intermediate molecule, ace2, this molecule is the key for the new coronavirus to enter the cell. If the cell has this key, then new coronavirus infection may occur.

Of course, ACE2 varies greatly between different species, so the authors chose to calculate whether ACE2 from different species and the new coronavirus can combine into a stable polymer as the detection standard.

The following figure shows a sequence similarity comparison

After calculation, it can be seen that there are still great differences in the combination of ACE2 and new coronavirus from different species to form stable complexes.

Then, at this time, two completely different results appeared.

1. The new coronavirus can infect a fish and a bird

Of the 35 birds tested only the blue tit shows an infection risk. Similarly, the Nile tilapia is the only fish out of the 72 in this study which has a binding energy favorable to infection.

The authors counted 35 bird species and found only one (the blue tit) at risk, and 72 fish species and found only one (the Nile tilapia) at risk.

2. The article concludes that the new coronavirus cannot infect fish and birds

Our results suggest that SARS-CoV-2 can infect a broad range of mammals––but not fish, birds or reptiles––which could serve as reservoirs of the virus, necessitating careful ongoing animal management and surveillance

In fact, from these two contents, we can see that the conclusion of the article seems to conflict with the research content in the article. You said that the new coronavirus cannot infect fish, so what about the one species that it infects? But you think it can infect, but the remaining 71 species of fish cannot be infected. It feels like a white horse is not a horse.

In fact, the problem lies here. It may be because this article has not been subject to peer review. The conclusion of the article is too affirmative, which in turn affects its scientific nature.

This article is a preprint and has not been certified by peer review

The correct way to write it should be: Theoretically, the new coronavirus cannot infect most fish, or the new coronavirus is difficult to infect fish.

In short, the facts are clear. Those who think that the new coronavirus cannot infect fish are mainly concerned about the title and abstract, or think that the possibility is small from a probability perspective. Those who think that the new coronavirus may infect fish need to emphasize the degree of the word "possible", after all, there are two species that may be infected.

Therefore, it is generally believed that fish will not be infected with the new coronavirus. However, contamination is very likely.