The new issue of the US "Cell" magazine published a review article written by researchers from the Pasteur Institute in Cambodia, focusing on a new study of bat coronaviruses led by Chinese researchers. The article believes that this new research helps to understand the origin of the COVID-19 virus more deeply. The article also pointed out that from the research so far, the natural host of the COVID-19 virus is likely to be the chrysanthemum bat in Southeast Asia.
COVID-19 "cousin" virus
According to the article, researchers from Shandong Academy of Medical Sciences, Chinese Academy of Sciences and other institutions sequenced 411 bat samples collected from a small area of Yunnan from 2019 to 2020, and obtained the complete genomes of 24 coronaviruses. Among them are four types of coronaviruses called cousins of the COVID-19 virus, all of which are obtained from the chrysanthemum bat. This new research article is also published in this issue of "Cell" magazine.
The "cousins" of these four COVID-19 viruses are numbered RpYN06, RsYN04, RmYN05, and RmYN08, respectively. Among them, the genome of RpYN06 is 94.5% similar to the COVID-19 virus, ranking second among all known viruses so far, second only to the bat coronavirus RaTG13 previously reported by the Wuhan Institute of Virology. RsYN04, RmYN05, and RmYN08 are similar to the coronaviruses previously collected from pangolins.
How did the ancestors of the COVID-19 virus obtain the ability to jump from bats to humans? This is a key issue in traceability research. The COVID-19 virus invades the human body through the combination of the spike protein on the surface and the human cell receptor "Angiotensin Converting Enzyme 2 (ACE2)". Therefore, the evolution of the spike protein is the key to whether it can infect the human body.
Judging from the four newly reported coronaviruses related to the COVID-19 virus, the spike protein region of this type of virus has undergone complex genetic recombination and presents diversity. Although RpYN06 is closer to the COVID-19 virus in the entire genome, its spike protein cannot bind to the ACE2 receptor. In contrast, RsYN04 is closer to pangolin coronavirus, but its spike protein has a weak ability to bind to ACE2.
Four unsolved mysteries
This review article believes that the above-mentioned new research provides clues for in-depth understanding of the origin of the COVID-19 virus. However, there are still four unsolved mysteries about the origin of the COVID-19 virus.
First of all, what kind of animal directly infects the COVID-19 virus to humans? Like most zoonotic viruses, the COVID-19 virus is likely to be introduced into humans via an intermediate host. So far, the coronavirus acquired in pangolins is the closest to the COVID-19 virus besides the bat coronavirus. However, researchers believe that the coronavirus in pangolins may be produced by "convergent evolution." It is not the animal host that directly introduces the COVID-19 virus into humans, and it is difficult to determine the animal host that directly infects the COVID-19 virus to humans.
Second, in nature, where did the COVID-19 virus originate? According to existing studies, the natural host of the COVID-19 virus is bats, which are likely to be chrysanthemum bats living in Southeast Asia. A variety of chrysanthemum bats have been found to carry coronaviruses related to the COVID-19 virus. The distribution areas and behaviors of these chrysanthemum bats overlap, which is more conducive to the spread, spread and reorganization of the virus. The diversity and ubiquity of viruses, high population density, and abundant potential intermediate host species have made Southeast Asia a hot spot for emerging infectious diseases.
Third, can you find "Bat Zero" or "Patient Zero"? It may not be found. The continuous evolution and reorganization of the COVID-19 virus makes it increasingly difficult to determine its origin. As a natural host, bats carrying the COVID-19 virus may not even show symptoms. In bats, the COVID-19 virus is likely to exist in the form of "quasi-species". Quasispecies means that the virus produces many mutant strains under the selective pressure of the host, among which one or several mutant strains will be dominant under certain conditions. The COVID-19 virus began to spread, adapt and continue to mutate in the population, which is likely to be far earlier than the time of the first case report.
Fourth, will there be a new human disease pandemic in the future? There is no doubt about this. So far, three-quarters of human diseases are of animal origin, but scientists still know very little about zoonotic diseases. The deterioration of the environment caused by urbanization and climate change increases the risk of new diseases. Researchers around the world should continue to work hard to find the origin of the virus, systematically assess the pathogens of zoonotic diseases that may cause a pandemic, and reduce the risk of future pandemics by improving biosecurity, strengthening species protection, and reducing human impact on the environment.
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