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The World Health Organization announced that a variant of coronavirus was officially confirmed as the pathogen that caused atypical pneumonia. Scientists say that the mutant coronavirus is related to influenza virus, but it is very unique and has never been found in humans before. Scientists named it "SARS virus" (SARS is the English abbreviation of SARS scientific name). 1965, a virus named B8 14 was isolated from the nasal wash of patients with cold by medical experts using the method of human embryonic trachea culture. Subsequently, Hamre et al. isolated a similar virus from human embryonic kidney cells, and the representative strain was named 229E virus. In 1967, Mclntosh et al. isolated a batch of viruses from cold patients by human embryonic trachea culture, and its representative strain was OC43 strain. From 65438 to 0968, Almeida et al. studied the morphology of these viruses, and observed by electron microscope that the envelope of these viruses had spinous processes similar to coronavirus, so they proposed to name these viruses coronavirus. Hong Kong health experts ruled out the possibility of influenza A and influenza B viruses, but not H5N 1 avian influenza virus in 1997. The country was officially named Coronaviridae on 1975. Hong Kong health officials said that SARS was usually caused by viruses, such as influenza virus, adenovirus and other respiratory viruses. Sars may also be caused by organisms. Coronavirus infection is very common all over the world, and antibodies against coronavirus are common in people, and adults are higher than children. Different countries reported different antibody positive rates. In the past, the positive rate of coronavirus antibody in China was 30% to 60%, and that in the former Soviet Union was 53% to 97%.

1937 coronavirus was isolated from chicken for the first time. 1965, the first human coronavirus was isolated. It was named "coronavirus" because under the electron microscope, there were obvious rod-shaped particles protruding from its outer membrane, which looked like the crown of medieval European emperors.

1975, the virus nomenclature Committee officially named it Coronaviridae. According to the serological characteristics and nucleotide sequence differences of viruses, Coronaviridae can be divided into two genera: Coronavirus and Circovirus. The representative strain of coronavirus family is avian infectious bronchitis virus (IBV).

Severe acute respiratory syndrome (SARS), which ravaged the world from the winter of 2002 to the spring of 2003, is a kind of coronavirus family and coronavirus genus.

Morphogenesis

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Coronavirus particles are irregular in shape and about 60-220nm in diameter. Virus particles are wrapped by a layer of fat membrane, and there are three kinds of glycoproteins on the surface of the membrane: spike glycoprotein (S, the receptor binding site, cell lysis and major antigen site); Small envelope glycoprotein (e, envelope protein); Membrane glycoprotein (M, responsible for transmembrane transport of nutrients, budding release of newborn virus and formation of virus envelope). A few species also have hemagglutinin glycoprotein (HE protein, hemagglutinin-esterase). The nucleic acid of coronavirus is non-segmented single-stranded (+) RNA with a length of 27-3 1kd. It is the longest RNA nucleic acid chain in RNA virus, which has the unique and important structural characteristics of positive-strand RNA: there is a methylated "hat" at the 5' end of RNA chain and a PolyA "tail" structure at the 3' end. This structure is very similar to eukaryotic mRNA, and it is also an important structural basis for its genomic RNA to play the role of translation template, thus omitting the transcription process of RNA-DNA-RNA. The recombination rate between RNA and RNA of coronavirus is very high, and the variation of virus is due to this high recombination rate. After recombination, the RNA sequence has changed, the amino acid sequence encoded by nucleic acid has also changed, and the protein of amino acid has also changed accordingly, thus changing its antigenicity. The result of antigenicity change is that the original vaccine is invalid and the immunity is invalid.

The viral RNA polymerase required for RNA virus replication does not exist in the mature particles of coronavirus. After viral RNA enters the host cell, it is directly used as a translation template to express viral RNA polymerase. Then the enzyme is used to complete the transcription and synthesis of negative-strand RNA (subgenomic RNA), the synthesis of various structural protein mRNA, and the replication of viral genomic RNA. There is no post-transcriptional modification and shearing process in the synthesis of mature mRNA of various structural proteins of coronavirus. On the contrary, by recognizing the specific transcription regulatory sequence (TSR) and through the "discontinuous transcription" mechanism, all components of a mature mRNA are selectively transcribed from negative sense RNA at one time. After the replication of structural proteins and genomic RNA is completed, new coronavirus particles will be assembled on the endoplasmic reticulum of the host cell and secreted out of the cell through Golgi apparatus to complete its life cycle.

Epidemiology of coronavirus

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Coronavirus infection is very common all over the world.

So far, about 15 different coronavirus strains have been found, which can infect many mammals and birds, and some can make people sick.

Human diseases caused by coronavirus are mainly respiratory infections (including severe acute respiratory syndrome, SARS). The virus is sensitive to temperature and grows well at 33℃, but it is inhibited at 35℃. Because of this feature, winter and early spring are the epidemic seasons of this virus disease. Coronavirus is one of the main pathogens of the common cold in adults, and the infection rate in children is high, mainly in the upper respiratory tract and rarely in the lower respiratory tract. In addition, it can also cause acute gastroenteritis in infants and newborns. The main symptoms are watery stool, fever and vomiting, which can be pulled 10 times a day or more. In severe cases, even bloody stools appear, and a few cases can cause nervous system syndrome.

Viruses mostly grow in epithelial cells, can also infect liver, kidney, heart and eyes, and can also grow in other cell types (such as macrophages). At present, there is no animal model suitable for human coronavirus research (human disease animal model), which refers to animals that simulate human diseases established in various medical research. Animal disease models are mainly used in experimental physiology, experimental pathology and experimental therapeutics (including the screening of new drugs), so it is very difficult to isolate coronavirus, which can only be isolated by organ culture of human hepatocytes, trachea and nasal mucosa cells. It is also difficult to reproduce viruses with the above materials.

The serotype and antigenic variation of coronavirus are unknown. Coronavirus can be repeatedly infected, indicating that there are many serotypes (at least 4 known) and many antigen variations, which makes it difficult to immunize. At present, there are no specific preventive and therapeutic drugs.

Transmission routes and preventive measures

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Coronavirus is excreted by respiratory secretions, spread by oral liquid, sneezing and contact, and spread by air droplets. The peak of infection is in autumn and winter and early spring. Viruses are sensitive to heat, and ultraviolet rays, Lysol, 0. 1% peracetic acid and 1% cliolin can kill viruses in a short time.

There are specific preventive measures, that is, targeted preventive measures (it is possible to develop vaccines, but it will take a long time to solve the problem of virus reproduction) and non-specific preventive measures (that is, measures to prevent respiratory infectious diseases in spring, such as keeping warm, washing hands, ventilation, avoiding excessive fatigue and contact with patients, and going to crowded public places less).