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Science: Outline of the COVID-19 spread

Science: Outline of the COVID-19 spread. Chinese Reserachers published the latest article outlining the spread of the new coronavirus.

On January 8, 2021, Shi Zhengli and Zhou Peng, researchers at the Wuhan Institute of Virology, Chinese Academy of Sciences, published a review article on the spread of the new coronavirus in the Science magazine: SARS-CoV-2 spillover events. The system outlines the current ways of the new coronavirus spreading to humans, and points out that more scientific research is needed in terms of tracing the natural host of the new coronavirus and the impact of the new coronavirus on human health after mutation in animals.

Severe Acute Respiratory Syndrome (SARS, 2003), Middle East Respiratory Syndrome (MERS, 2012) and Novel Coronavirus Pneumonia (COVID-19, 2019) have all erupted in the past two decades and are caused by different strains of coronavirus cause. Many viruses are believed to originate from bats and then spread to humans through intermediate hosts. SARS virus originates from civet cats in the wild animal market; MERS virus originates from dromedary camels; however, we have not yet determined the direct source of the COVID-19 pathogen.

Oude Munnink and others reported in depth the occurrence of COVID-19 virus infections in 16 mink farm animals and workers working and living in the Netherlands. Of the 97 farmers, workers and their close contacts, 66 were infected with the COVID-19 virus. Some The patient’s strain has animal sequence characteristics, which provides evidence for the new coronavirus to spill back and forth between animals and people in the mink farm (Note: The virus in nature crosses populations and spreads to people or other animals).

In addition to mink, a variety of wild or domestic animals may also carry the new coronavirus or its related viruses. Experimental virus infection test and virus antigen-receptor affinity test confirmed that the new coronavirus has a wide host range. After the outbreak of COVID-19, some research groups reported SARS-related coronaviruses in Chinese horseshoe bats and pangolins smuggled from South Asia, but the genome sequence comparison results did not have a direct ancestor of the new coronavirus. Domestic cats, domestic dogs and park tigers have also been found to be infected by patients with the COVID-19 virus, but there is also no evidence that they can infect humans. Therefore, they are unlikely to be the host of the source of the new coronavirus.

So far, the World Organization for Animal Health has reported new coronavirus infections in mink farms in 8 countries (Netherlands, Denmark, Spain, France, Sweden, Italy, the United States and Greece). In addition to the spread of farm animals to people, the food cold chain has attracted great attention. In many cities in China, several small-scale COVID-19 outbreaks have been caused by seafood or pork contaminated by the virus overseas. There is evidence that the new coronavirus can survive on the surface of meat and cold food packaging for 3 weeks and is still infectious. Therefore, the meat of animals infected with the new coronavirus or food packaging contaminated by the virus may be a source of human infection.

SARS-CoV-2 possible transmission chain

Most animals infected with the new coronavirus have no obvious clinical manifestations and cannot be screened without routine diagnosis. Large-scale “culling” of mink farms is an effective way to prevent further spread of the virus. However, this does not apply to all domestic animals (if other species are found to be hosts of the new coronavirus). Therefore, out of prudent consideration, strict isolation measures should be implemented in poultry farms with high-density populations. Since the virus can spread between certain animals (such as mink) and humans, similar control strategies should also be implemented in important occupational groups such as animal breeders, zookeepers or slaughterhouse workers. However, the evidence for the spread of the new coronavirus in other animals (except mink) and humans is still relatively limited. The scientific community should conduct research on whether other domestic animals can carry the new coronavirus, whether it can be transmitted to humans, and other related factors of virus spillage.

The current scientific community has detected the cumulative mutations of the new coronavirus, but the RNA genome of the new coronavirus seems to be relatively stable during the spread of the population. It is generally believed that coronaviruses tend to evolve rapidly as they jump to different species. In order to maintain a low replication error rate, coronaviruses encode several RNA processing and proofreading enzymes to improve the fidelity of virus replication.

However, in order to adapt to new species hosts, viruses tend to sacrifice this fidelity. Coronavirus spike protein is prone to mutation. It is the primary key molecule for the virus to infect the host, so it faces the strongest selection pressure. People have observed this kind of molecular evolution in the SARS virus genome. The early stage of disease transmission (civet cat to human) is more pressured to adapt than in the later stage (between humans).

The mutated new coronavirus in animals may increase its incidence and spread in humans. Five variants of new coronavirus (Cluster 1-5) were found in mink. In Denmark, the immunogenicity of Cluster 5 to the sera of patients with COVID-19 pneumonia is lower than that of human new coronavirus, because the mutation of the different strain is located in the spike protein of the virus. The Cluster 5 strain has infected at least 12 people, but the clinical manifestations, severity, and transmission between infected people are similar to other new coronavirus strains circulating in humans. At present, there is no evidence that any mutation of the mink COVID-19 virus strain can evade the neutralizing effect of antibodies against human epidemic strains. However, considering the possible spillover risk of the new coronavirus between humans and certain animals, it is necessary to closely monitor the viral genome mutations from infected animals and humans, especially the genomes that affect diagnostic tests, antiviral drugs and vaccine development areas.

The vaccine will help control the COVID-19 pneumonia. If the virus continues to spill from animals, vaccines against currently circulating strains may face challenges. The viral genome is likely to mutate during the spread between animal and human species, causing people to wonder whether current vaccines can prevent new strains in the future. Extensive sequencing of animal and human viral genomes and global data sharing will be the core work of monitoring the impact of key mutations in the viral genome on vaccine efficacy. Experimental research should detect whether the emergent mutations affect the main characteristics of the virus, including pathogenesis, immunogenicity and cross-neutralization. In addition, preparations should be made for the development of new variant virus vaccines. In the long run, we should also consider vaccinating animals to avoid agricultural economic losses.

The genome sequence of the coronavirus carried by bats or pangolins is 90-96% similar to the human new coronavirus, but whether they are the animal source of the first human outbreak is still controversial. Genome evolution analysis of bats and pangolin viruses shows that before the COVID-19 pneumonia pandemic, the virus has undergone further adaptation in animal hosts or humans. Therefore, animals with a high population density, through natural selection and qualified new coronavirus receptor ACE2, may become the direct ancestral host of the new coronavirus. Another argument is about the source of the new coronavirus. Current data question the origin of the new coronavirus from animals in the Wuhan seafood market.

In view of the detection of the new coronavirus on the surface of some imported food packaging, contact with contaminated and uncooked food may be an important way for the spread of the new coronavirus. Recently, antibodies to the new coronavirus have been detected in serum samples of overseas personnel collected before the outbreak of the COVID-19 pneumonia, which indicates that the COVID-19 virus has existed for some time before the first case was reported in Wuhan. Before the outbreak, samples from mink, other susceptible animals, and people should be retrospectively investigated to identify the host of the virus ancestors and determine when the virus spilled into humans.

(sourcechinanet, reference only)

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