MindMap Gallery Introduction to virology mind map
Mind map of Chapter 13 Introduction to Virology (General Introduction to Viruses) in the 8th edition of Microbiology and Immunology, including virus infection and immunity, virus morphology, structure and classification, etc.
Edited at 2023-11-06 23:17:14El cáncer de pulmón es un tumor maligno que se origina en la mucosa bronquial o las glándulas de los pulmones. Es uno de los tumores malignos con mayor morbilidad y mortalidad y mayor amenaza para la salud y la vida humana.
La diabetes es una enfermedad crónica con hiperglucemia como signo principal. Es causada principalmente por una disminución en la secreción de insulina causada por una disfunción de las células de los islotes pancreáticos, o porque el cuerpo es insensible a la acción de la insulina (es decir, resistencia a la insulina), o ambas cosas. la glucosa en la sangre es ineficaz para ser utilizada y almacenada.
El sistema digestivo es uno de los nueve sistemas principales del cuerpo humano y es el principal responsable de la ingesta, digestión, absorción y excreción de los alimentos. Consta de dos partes principales: el tracto digestivo y las glándulas digestivas.
El cáncer de pulmón es un tumor maligno que se origina en la mucosa bronquial o las glándulas de los pulmones. Es uno de los tumores malignos con mayor morbilidad y mortalidad y mayor amenaza para la salud y la vida humana.
La diabetes es una enfermedad crónica con hiperglucemia como signo principal. Es causada principalmente por una disminución en la secreción de insulina causada por una disfunción de las células de los islotes pancreáticos, o porque el cuerpo es insensible a la acción de la insulina (es decir, resistencia a la insulina), o ambas cosas. la glucosa en la sangre es ineficaz para ser utilizada y almacenada.
El sistema digestivo es uno de los nueve sistemas principales del cuerpo humano y es el principal responsable de la ingesta, digestión, absorción y excreción de los alimentos. Consta de dos partes principales: el tracto digestivo y las glándulas digestivas.
General introduction to viruses
Viruses are a type of non-cellular microorganisms that are small in size, simple in structure, containing only a single nucleic acid, obligate intracellular parasitism, and increase their value through replication. Its main characteristics are: 1. The size is very small and requires an electron microscope to magnify tens to hundreds of thousands of times before it can be seen; 2. There is no complete cell structure, and non-enveloped viruses are mainly composed of core nucleic acid and protein shell; 3. .Contains only one kind of nucleic acid (RNA or DNA) as its genetic material; 4. Obligate intracellular parasitism; 5. Proliferates by replication; 6. Insensitive to antibacterial drugs
Virus morphology, structure and classification
Size and shape of virus: The complete mature virus particle is called a virion, which is the structural form of the virus outside the cell. It has a typical morphological structure and is infectious. Virion size is measured in nanometers or nanometers. The size of various virions varies greatly, the largest is about 300nm, such as poxvirus; the smallest is only 20nm, such as microvirus. Most viruses are spherical or nearly spherical, a few are wafer-shaped, filamentous, bullet-shaped and brick-shaped, and phages are tadpole-shaped.
Structure and chemical composition of viruses
structure
Core: Located in the center of the virion, it is mainly single- or double-stranded DNA or RNA, which constitutes the viral genome and provides genetic information for viral replication, inheritance, and mutation. It may also contain a small amount of functional proteins such as viral nucleic acid polymerase or transcriptase.
Capsid: A protein shell surrounding the core. The capsid is antigenic and is the main antigenic component of the virion. It can protect viral nucleic acid from damage by nucleases or other factors in the environment, and can mediate virus entry into host cells. The capsid is composed of a certain number of capsomeres, each capsomere is called a morphological subunit, and is composed of one or more polypeptide molecules. These polypeptide molecules are called chemical subunits or structural subunits.
Helical symmetry: Capsomeres are symmetrically arranged along the spirally coiled viral nucleic acid chain.
Icosahedral symmetry: The nucleic acid is concentrated into a spherical or approximately spherical shape, and the capsomeres on the periphery are arranged in an icosahedral symmetry. Each face of the icosahedron is an equilateral triangle and is composed of a tessellation of capsomers. The capsomere at the top of most virions is surrounded by 5 identical capsomeres, called a penton; the capsomere on the triangular surface is surrounded by 6 identical capsomers, called a hexon. In most cases, the capsid of the virus is formed around the nucleic acid, but it can also be seen that an empty capsid is formed first and then filled with nucleic acid.
Compound symmetry type: The virion structure is complex, and the capsid has both helical symmetry and icosahedral symmetry.
Envelope: It is obtained when certain viruses pass through host cells during the maturation process and are released out of the host cells by budding. It contains components of the host cell membrane or nuclear membrane, including lipids and a small amount of sugars. There are often protrusions of different shapes on the surface of the capsule, which are called capsule grains or spikes. The main function of the envelope is to maintain the structural integrity of the virion. The phospholipids, cholesterol and neutral fats contained in the envelope can strengthen the structure of the virion. The lipids of the virion envelope from the host cell membrane are homologous to the cellular lipid components and are easy to affinity and fuse with each other. Therefore, the envelope also plays a role in assisting viral infection. In addition, the envelope is virus species and type specific and is one of the basis for virus identification and typing. The envelope constitutes the surface antigen of the virion and is closely related to pathogenicity and immunity. Enveloped viruses are called enveloped viruses, and non-enveloped viruses are called naked viruses. Most human and animal viruses are enveloped.
chemical components
Nucleic acid: Its chemical composition is DNA or RNA. Main functions: 1. Virus replication; 2. Determining the characteristics of the virus; 3. Infectious.
Viral protein: Protein is the main component of the virus, accounting for approximately 70% of the total weight of the virion. Main functions: 1. Protect viral nucleic acid: the capsid protein surrounds the nucleic acid, avoiding damage to the nucleic acid by nucleases and other physical and chemical factors in the environment; 2. Participate in the infection process: the protrusions of the capsid protein and envelope protein can specifically It adsorbs to receptors on the surface of susceptible cells, mediates viral nucleic acid to enter host cells, and causes infection; 3. It has antigenicity: the capsid protein is a good antigen. After the virus enters the body, it can induce specific humoral immunity and cellular immunity.
Lipids and sugars: The lipids of virions mainly exist in the envelope. Some viruses contain a small amount of sugars in the form of glycoproteins, which are also one of the surface components of the envelope. The glycoproteins of most viruses can bind to host cell surface receptors and are called viral adsorption proteins.
The classification of viruses is based on: 1. The nature and structure of nucleic acids; 2. The size and shape of virus particles; 3. Capsid symmetry and number of capsomeres; 4. Whether or not there is an envelope; 5. Sensitivity to physical and chemical factors; 6 .Antigenicity; 7. Biological properties
multiplication of virus
Replication cycle: 1. Adsorption; 2. Penetration (swallowing, fusion); 3. Shelling; 4. Biosynthesis; 5. Assembly and release (cytolysis release, budding release)
Abnormal value-added and interference phenomena: frustrated infections, defective viruses
Artificial culture of viruses
animal vaccination
Chicken embryo culture
Tissue (cell) culture
primary cell culture
diploid cell culture
Passage cell culture
Principles of detection, prevention and treatment of viral infections
Collection and submission of specimens: 1. Collect appropriate specimens based on clinical diagnosis and disease stage, such as nasopharyngeal secretions for upper respiratory tract infections, cerebrospinal fluid for nervous system infections, feces for intestinal infections, and blood for viremia, etc. 2. Specimens must be collected under strict aseptic procedures, and antibiotics should be used for specimens that contain miscellaneous bacteria. Generally, penicillin, streptomycin, or gentamicin, amphotericin, etc. are added as needed. 3. After collecting the specimens, they should be stored at low temperature and sent for inspection as soon as possible. 4. For specimens used for serological diagnosis, one serum should be taken from each of the acute phase and the recovery phase. If the serum titer in the recovery phase is 4 times or more higher than that in the acute phase, it will have diagnostic significance.
Isolation and identification of virus: 1.50% tissue cell infection dose determination, 2. Red blood cell agglutination test, 3. Plaque formation test
Serological diagnosis of viral infection: 1. Detection of viral antigen markers, 2. Detection of specific IgM antibodies
Viral nucleic acid detection: 1. Nucleic acid hybridization technology, 2. Nucleic acid amplification method
Principles of prevention and treatment of viral infections: (1) Artificial automatic immunity: 1. Inactivated vaccine, 2. Live attenuated vaccine, 3. Subunit vaccine, 4. Genetically engineered vaccine (2) Artificial passive vaccines (3) Drug treatment: 1. Nucleoside drugs, 2. Viral protease inhibitors, 3. Interferons and their inducers
Viral infection and immunity
Mode of transmission of viral infection: The virus is mainly transmitted through damaged skin and mucous membranes (eyes, respiratory tract, digestive tract or genitourinary tract), but under certain conditions it can directly enter the blood circulation (such as blood transfusion, mechanical injury, insect bites, etc.) and infect the body. . Most viruses enter the host body through one route, but viruses that infect through multiple routes are also seen, such as HIV. Inhalation is currently considered the most common route of viral infection. There are two modes of transmission of viral infections: horizontal transmission and vertical transmission. Horizontal transmission is the mode of transmission of most viruses, while vertical transmission of viruses from parents to offspring through the placenta or birth canal can also be seen in many viruses, such as rubella virus , cytomegalovirus, HIV and hepatitis B virus, etc.
Pathogenesis of viral infection
Pathogenic effects on host cells
Cytocidal effect: After the virus replicates in the host cell, a large number of progeny viruses can be released at once in a very short period of time, and the cells are lysed and die. This situation is called cytocidal infection.
steady state infection
Cell fusion: Certain viral enzymes or lysosomal enzymes released by infected cells can change the membrane of infected cells, causing the infected cells to fuse with neighboring cells. The virus spreads to uninfected cells by means of cell fusion.
Antigens encoded by viral genes appear on the cell surface: New antigens encoded by viral genes often appear on the cell membrane of virus-infected cells.
Inclusion body formation: Virus-infected cells form. Using an ordinary light microscope, you can see round or oval plaques that are different from normal cell structure and coloration, called inclusion bodies. Some are located in the cytoplasm (poxviruses), some in the nucleus (herpesviruses), or both (measles viruses); some are eosinophilic or basophilic, depending on the type of virus.
Apoptosis: Viral infection can lead to host cell apoptosis, a process that may promote virus release from the cell but also limits the number of virions produced by the viral "factory."
Gene integration and cell transformation: Certain DNA viruses and retroviruses can integrate genes into the host cell genome during infection, which can lead to cell transformation, faster proliferation, and loss of cell-to-cell contact inhibition. Gene integration or cell transformation is closely related to tumor formation.
Immunopathological effects of viral infection
Antibody-mediated immunopathological effects: The envelope protein and capsid protein of the virus are both good antigens and can stimulate the body to produce corresponding antibodies. The combination of antibodies and antigens can prevent the spread of the virus and cause the virus to be cleared. However, after infection, many viral antigens can appear on the surface of host cells. After binding to antibodies, they activate complement and lead to the destruction of host cells, which is a type II hypersensitivity reaction. Another mechanism of antibody-mediated injury is type III hypersensitivity reactions caused by antigen-antibody complexes. The complexes formed by viral antigens and antibodies are deposited in the blood circulation and cause damage. Patients with chronic viral hepatitis often experience joint symptoms, which are related to the deposition of immune complexes in the synovium of joints causing arthritis.
Cell-mediated immunopathological effects: Cellular immunity is an important mechanism for the host to clear intracellular viruses. The killing caused by CTL recognition of viral antigens on the target cell membrane can terminate intracellular viral replication and plays a key role in recovery after infection. However, cellular immunity also damages host cells and causes functional disorders. This may be an important aspect in the pathogenesis of the virus and is a type IV hypersensitivity reaction.
Immunosuppressive effect: Certain viral infections can suppress the body's immune function, such as measles virus, rubella virus, and cytomegalovirus. Some viral infections can even cause a complete defect in the entire immune system, such as HIV infection. Immunosuppression caused by viral infection can activate latent viruses in the body or promote the growth of certain tumors, complicating the disease and possibly becoming one of the causes of persistent viral infection.
Types of viral infections
latent infection and overt infection
Hidden infection: the virus enters the body without causing clinical symptoms
Overt infection: clinical symptoms caused by viral infection
Acute infection: After the virus invades the body, it proliferates in the cells and develops after an incubation period of several days or even weeks, causing target cell damage and death, resulting in tissue and organ damage and dysfunction, and clinical symptoms. However, starting from the incubation period, the host mobilizes non-specific and specific immune mechanisms to eliminate the virus. Except for fatal cases, the host can generally clear the virus and enter the recovery period within a period of time after symptoms appear. It is characterized by a short incubation period, an acute onset, a course of several days to several weeks, and specific immunity is often acquired after the disease.
persistent infection
Latent infection: After dominant or latent infection with some viruses, the viral genes exist in cells and do not replicate. However, under certain conditions, the virus is activated and starts to replicate again, causing the disease to relapse. The presence of the virus can be detected during overt infection, but not during the incubation period.
Chronic infection: The virus is not completely cleared after overt or latent infection, and the virus can continue to be detected in the blood, so it can be spread through blood transfusions and injections. Patients may show mild or no clinical symptoms, but they often have recurring attacks and are not cured.
Chronic viral infection: a viral infection that develops chronically and becomes progressively worse. There is a long incubation period after viral infection, which can last for months, years or even decades. After the onset of symptoms, they progressively worsened and eventually led to death.
Delayed complications of acute viral infection
antiviral immunity
innate immunity
Interferon
NK cells
adaptive immunity
Humoral immunity
cellular immunity
Physical and chemical factors on viruses
physical factors
Temperature: Most viruses are resistant to cold but not heat
pH: Most viruses are stable within the pH range of 5-9
Rays and UV: Gamma rays, X-rays and UV rays can all inactivate viruses
chemical factors
Lipid solvent: The envelope of the virus contains lipid components and is easily dissolved by lipid solvents such as ether, chloroform, and deoxycholate.
Phenols: Phenol and its derivatives are protein denaturants and can be used as virus disinfectants
Oxidants, halogens and their compounds: viruses are sensitive to these chemicals