How does virus infect human body cause disease?

According to the latest news from the National Health and Medical Commission, as of 24:00 on January 21, 440 cases of pneumonia diagnosed with new coronavirus infection have been reported in 13 provinces autonomous regions, municipalities in China, and a total of 9 death cases have been reported.

Nobel Prize in Medicine and Physiology in 1960, Peter Midawa, once defined the virus as "a virus is a piece of nucleic acid surrounded by bad news." In other words, a virus is a little genetic material-a single nucleic acid [deoxygenationA genetic unit of ribonucleic acid DNA or ribonucleic acid RNA] and the shell of a protein molecule that encapsulates this nucleic acid. In other words, a virus is the simplest heritable form on our planet.

In the biological world, viruses, plants, and animals are three major groups of organisms. Various plants and animals, including bacteria and protozoa, are organisms composed of cells. Viruses have no cell structure and are absolute parasites.The virus uses its contained genetic information to infect cells and uses the cell's metabolic "machines" to continuously replicate itself in large numbers. Only the infected cells can reproduce, and the copied virus infects new cells. Not only that, the virusIn order to adapt to changes in the environment, its genes will often mutate, and those with weak virulence will unexpectedly become extremely virulent; especially when two or more viruses infect the same cell, the genes of a virusFragments will generate new viruses through genetic recombination or reassortment with gene fragments of another virus. It is because the virus's simple structure and great variability make them the easiest to change virulence and become harmful organisms.

What are the characteristics of the virus?

There are many types of viruses. It is not clear how many viruses there are on our planet. At present, there are about 4,000 types of viruses that have been recognized and classified. Among them, about 1 have medical significance and may be infectious./ 10, 400 or so. But we already know that everywhere there is a virus, it can cause human infection.

Of course, plants and animals are no exception. There are corresponding viruses and viral diseases. Generally speaking, plant viruses cannot infect humans; however, some viruses can infect both animals and humans. Both humans and animals canInfected viruses are called "zoo zoonotic viruses", such as rabies virus, mad cow virus, avian influenza virus, etc. Although the size, structure, and host range of different viruses are different, they have the following basic similarities:

1 The volume of the virus is very small 10 ~ 300nm. It can pass through the finest bacterial filter. Generally, it needs to use an electron microscope and magnify 10,000 times to see;

2 The virus is composed of RNA or DNA genome surrounded by a protective protein shell, and is mostly covered by a lipoprotein outer membrane outside the core shell;

3 Viruses can only reproduce in cells, relying entirely on host cells to synthesize and provide energy, and have strict intracellular parasitism;

4 Before the virus replicates in the cell, it is necessary to take off the shell to release the genome;

5 Viruses generally have resistance to antibiotics, so the use of antibiotics to treat viral diseases is generally ineffective or has little effect.

Compared with other organisms, the genome of the virus is smaller, such as measles virus, polio virus, Ebola virus, hantavirus and human immunodeficiency virus HIV, all of which have less than 10 genes,The largest variola virus also has only 200 to 400 genes. The ratio of 5,000 to 10,000 genes possessed by the virus with the largest number of genes and the smallest bacteria is comparable to that of 30,000 to 50,000 genes possessed by human cells., Its amount of genetic information seems insignificant. But even with such a small number of genes, the virus can destroy thousands of humans more than its genes!

How does virus infect human body cause disease?

Scientific research shows that there are three ways for the virus to cause disease :

One is that the virus or its protein directly kills the cell, and some viruses destroy the cell while they are released from the cell outward;

Second, the virus changes the function of the cell, making the cell unable to synthesize an important protein. For example, non-lethal virus infects some cells, making them unable to produce enough hormones;

The third is that the virus destroys the infected cells and produces various immune damages. Some immune responses produced by the body to the virus may accidentally hurt itself. For example, the antigen-antibody complex formed by the virus is deposited on the blood vessel wall or kidney cells, which can causeDirect or indirect damage.

A variety of viruses are known to be able to infect humans, but the conditions of infection are very different: some have clinical symptoms, some have subclinical infections or no obvious clinical symptoms; some viral infections are acute or self-limitingCan obtain lifelong immunity; some are in a dormant state and become active again after a period of time or under appropriate conditions, and some re-infect those who have been infected and have some immunity; some viruses, such as hepatitis B virus, bothIt can cause acute infection and chronic infection. Among them, the acute epidemic virus infection has the greatest impact on people and the consequences are more serious. For example, acute viral encephalitis, although the incidence is not too high, but the mortality rate is high; on the contrary,Viral diseases, such as viral influenza, have a low mortality rate, can cause high morbidity, and can lead to loss of labor. Some viral diseases have no obvious clinical symptoms in the short term, with incubation periods of several years, or even more than ten years, such as giant cellsThis is the case with viral and rubella virus infections. Some like mad cow disease and AIDS do not develop for a long time, and once they become infected, they are almost 100% fatal. From the clinical manifestationsLooking at it, some different types of viruses can produce the same clinical symptoms, such as many viruses can cause clinical symptoms of colds; such as adenovirus, influenza virus, parainfluenza virus, mumps virus, respiratory syncytial virus, coronavirus,Rhinoviruses can cause acute respiratory infections; for example, enteroviruses coxsackie virus, poliovirus, ecovirus, etc., arboviruses Saint Louis encephalitis virus, oriental equine encephalitis virus, western equineEncephalitis virus, Venezuelan equine encephalitis virus, Japanese encephalitis virus, rabies virus, etc. can cause diseases of the central nervous system. Some viruses can cause completely different clinical symptoms, such as cytomegalovirus, in pregnant women.Infection in the uterus can cause fetal malformations; small heads, stunting, deafness, cataracts, hepatosplenomegaly, etc. after the baby is born; adult infection HIV can cause infectious mononucleosis,Patients with immunosuppression are prone to systemic spread infections after infection.

Where does the virus come from?

The question of the origin of the virus is still a mystery. Some people have proposed the "degeneration hypothesis": the nucleic acid of the virus may have evolved from the genes of normal cells. Cells have undergone gene pairing, recombination and long-term mutation, which may allow the virus to acquire its own genesStructure. Usually, these viruses dormant in their host cells and are in a symbiotic or nearly symbiotic relationship with the cells. However, once the virus is transferred from one host to another, it will suddenly mutate to form a new gene mixture., These viruses that have previously been symbiotic with the cell acquire high levels of virulence.

If any virologist suspects that a canine pestilence virus or sheep scalp virus may mutate when it crosses the barriers of different species and enters the human body, thereby becoming a human measles virus. This speculation is not speculation, because the aforementionedThe genetic sequences of these three viruses are very similar. The similar genetic structure of these three viruses is likely to be caused by people living closely with domestic animals. Similarly, some kind of monkey virus may infect people and become human AIDS.Virus. This means that whenever a virus enters a new host, it may mutate, and the mutated virus can cause new serious infectious diseases. Although viral infectious diseases are terrible, humans are not helplessWith the development of science and technology, humans have gradually mastered the magic weapon to surrender these demons. Vaccines are currently the most effective means to control or even eliminate viral infectious diseases. Measles, polio, rubella and some viral encephalitis have been effective.Vaccines, humans have eliminated smallpox by relying on vaccinia. Scientists have also been looking for treatments for viral infectious diseasesDrugs, but for most acute viral diseases, effective preventive measures and treatment methods are still lacking. Therefore, humans need to work hard to completely overcome the virus plague.

Part of the content of this article comes from the magazine Knowledge is Power

Original author / Hong Tao Academician of the Chinese Academy of Engineering Wang Jianwei Associate Research Fellow, Chinese Center for Disease Control and Prevention

Reviewer / Li Bin Director of Popular Science Working Committee of Chinese Society of Cell Biology, Director and Researcher of Institute of Immunology, Shanghai Jiaotong University School of Medicine