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.

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.

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.

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

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.

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.

Hidden infection: the virus enters the body without causing clinical symptoms

Overt infection: clinical symptoms caused by viral 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

Interferon

NK cells

Humoral immunity

cellular immunity