Is it true that the fish tolerate Covid?

In mid-August, the media dispersed that in China they are now doing PCR tests for a coronavirus infection of even caught fish. We decided to check whether the fish can really be carriers of the disease or this strange precaution is not justified.

Information about PCR testing of fish appeared in mid-August in many media. In English they wrote about this BBC, The Guardian, CNN, and in Russian - Deutsche Welle, "New news","Komsomolskaya Truth","Moscow 24" And "RIA Novosti". It is reported that this is the initiative of the administration of the city of Syamyn in the province of Fujian. There are now checked not only fishermen who came from the sea, but also their catch: fish, crabs and even shrimp. The PCR tests of the fish are taken with a cotton swab from the oropharynx, in crabs-a flush on the underside of the shell, the media do not write about the method of testing shrimp. IN Internet Also placed many video And photo seafood testing process. Also reportedWhat a mandatory PCR testing every two weeks is now a hippo from the Wildlife Park to Khucjou, as well as giant pandas.

From numerous Scientific and popular publications About coronavirus infection in the media wide Known Information that the SARS-COV-2 virus “clings” to special lung tissue cells. More Detail publications indicate, What dot The input of the virus to the cell is an angiotensinoproting enzyme 2, or ACE2. One could conclude: since Covid “clings” for a certain enzyme in the lungs, and in fish and crustaceans, which include crabs, there are no lungs, which means that there is simply nowhere to attach the virus. However, not everything is so simple and obvious. 

Although ACE2 is most often written in the context of the pulmonary tissue, it is present in most body tissues: on membranes Enterocytes (intestinal cells), endothelial cells (lining the inner surface of arteries and veins), smooth muscle cells In most internal organs. MRNA for ACE2 was discovered Even in the cells of the cerebral cortex, brain stem and some other structures (for example, in striatum and hypothalamus). It is the presence of ACE2 on the neurons of the brain and its damage to the SARS-COV-2 virus Curses To the persistent loss of smell, steamy (a state where, instead of ordinary smells, a patient who has suffered a covid feels the fetid) and a neurological deficit also observed in Covid-19. 

At the same time ACE2 Expressed Not only in humans, but also other vertebrates and even invertebrates. The group of Chinese scientists in 2020 studied the structure of the ACE receptor in different species, compared the human and built a phylogenetic tree-a scheme that reflects the evolutionary relationships between different species.

Scientists have come to an unambiguous conclusion: the low genetic similarity of ACE2 in humans and fish nullifies the possibility of infecting a person with the virus of water food animals. At the same time, the study notes that there is a large group of mammals that are potentially susceptible to infection with coronaviral infection. The article was published in November 2020, respectively, submitted to the journal even earlier. Moreover, information about coronavirus infection in minks appeared also in November 2020, and at white -tailed deer - In 2021. Thus, theoretical calculations of Chinese scientists were confirmed in practice. 

Back in 2021, the World Animal Health Organization Published Data regarding the possibility of infection (high / low / absent), infection paths (in a natural environment or in the laboratory) and the presence of symptoms of infection in 16 species of animals, including agricultural. Poultry, pigs and cattle, even intentionally exposed to the virus, or did not infect at all, or the extremely small percentage of animals was infected. But the animals-companions (cats, rabbits, Syrian hamsters and ferrets) were infected with a high degree of probability. In April 2022, the organization Published Refined data on outbreaks among animals. Infections were recorded among otters, snow leopards, hyenas, bintorogs (representatives of the family of wyverr), hippos and ants. The only marine inhabitant in the list is the West Indian (or American) Lamantin, which belongs to vulnerable species, the hunt on which Forbidden. Moreover, as follows from the name of the animal, it lives along the Atlantic coast of North, Central and South America, and not off the coast of China.

Joint Chilean-Canadian study of 2021 He emphasizesthat fish, in principle, do not infect a person with zooneal (transmitted from animal to humans) infections. The transfer of the virus does not occur even when the fish is the carrier of the virus (for example, the Sea Lev-Migel virus, it is also known as Virus Vezicular Exantem Pig). Scientists note that cold -blooded animals are highly resistant to viruses of mammals and birds, which are replicated at a temperature of 37 ° C. Food and agricultural organization of united nations Notes: "There is no reason to assume that SARS-COV-2 can infect water food animals (for example, fluid fish, crustaceans, mollusks, amphibians)." 

The most complete study on the susceptibility of fish to coronaviral infection Spent In China in January 2022. A group of scientists from the Uthan Institute of virology infected the virus of three lines of fish cells containing achecceptors: a line of skin-headed gholana skin cells (type of carp fish), white amorous cupid kidneys (also carp) and caudal artery of the blue-winged sunny (a family of central stations). The Vero cell line (the kidney of the African green monkey) - one of the most popular lines used for scientific research in the field of biology and pharmacology - played the role of the control group. Fish cells were cultivated at a temperature of 24 ° C, and mammalian cells at 37 ° C. Then, behind the cellular lines, they “looked after” - the nutrients were introduced and the process of finding them in a living organism was imitated. In the future, neither immunofluorescent analysis (ELISA Test) nor PCR showed the presence of a virus on the cellular lines of fish, while the tests found the SARS-COV-2 virus on the Vero line, that is, the experimental conditions were favorable for the propagation of the virus in principle. Scientists came to the conclusion that SARS-COV-2 can be attached to fish cells, but cannot penetrate or replicate into fish cells. They explained this by the fact that among 20 key sites (certain elements) that interact with the SARS-COV-2 receptor domain, only one or two critical residues in each line of fish cells are identical to the human ACE2. In simple terms, fish receptors are so different from human that coronavirus “does not recognize them”. Scientists also took the cells of the HELA line (a cancer tumor of the human cervix) and using plasmid (small DNA molecules) imitated the lines of fish-zybra, thylapy, catfish, salmon and rainbow trout. The way the virus propagated well on the original HELA line and did not multiply on the modified one also confirmed that SARS-COV-2 cannot use ACE2 fish.

It is worth noting that the Chinese initiative to test the fish was criticized by scientists. For example, a professor at the Biomedical Sciences of the University of Hong Kong Jin Dunyan He called it Chinese initiative with an empty waste of resources. Chinese Users, in turn, Make a ridicule The initiative and offer the authorities to oblige fish to observe seven -day quarantine and limit their movements to the ocean.

Thus, the knowledge accumulated today indicates that none of the existing options for coronavirus infection infects fish, mollusks and crustaceans. Consequently, the Chinese initiative regarding marine inhabitants in the current conditions is useless, which cannot be said about testing the hippo, since these artricious coronavirus infection are still infected. At the same time, the virus is indeed can be determined On products, including seafood, if in the process of extraction or preparation the product or surface, which it touched, were contaminated (contaminated) with the virus. 

Image on the cover: South China Morning Post

Not true

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