Why do the symptoms of viral diseases differ?


Riyadh: Dr. Hassan Muhammad Sandakji

Medical reviews indicate that a viral infection (Viral Infection) may not always cause an acute viral disease (Acute Viral Disease), which appears quickly and inevitably.

The description of a “viral infection” originally includes the processes of entering the body and multiplying it in the host cell. As for the “acute viral disease”, it includes negative health effects that appear quickly as a result of the damage caused by this viral reproduction, and the damage resulting from the repercussions of the body’s immune system interactions with this viral infection.

Symptoms vary,

therefore, in cases of the same viral disease in a different group of people, there are patients who display severely ill symptoms that are different from other patients. And this appears in the form of asymptomatic patients who are classified as “carriers” of the disease, because they can infect others and cause viral disease accordingly. Or patients with symptoms of mild (Mild) or moderate (Moderate). In the few, the health condition may deteriorate severely (Sever) before they recover, and in other cases the viral disease becomes a chronic condition (Chronic).

It can explain the mechanisms of the emergence of many symptoms (symptoms) and signs (signs) associated with viral diseases, and the reasons for the severity of suffering some of them. As these symptoms and signs of disease differ because there are viral diseases that affect different areas of the body, such as the nervous system, the digestive system, the liver, the respiratory system, the eyes, the reproductive system, the skin, the heart, the blood or other parts of the body.

Reasons for the difference in symptoms

Despite the presence of different types of viruses that cause diseases, and despite the difference in the organs targeted for damage in case of infection with each type, medical sources note that there are several reasons and other factors for the difference in the degree of severity of symptoms and disease signs and their diversity among those with cases of viral diseases.

Knowing the mechanisms of these causes and factors may explain why organs are damaged without others in cases of infection with a certain type of virus, and it also explains the difference in the degree of appearance of different types of symptoms and pathological signs of the same viral infection, and also explains the quality of complications and repercussions for patients without others with the same viral disease.

This can be realized by reviewing three aspects, namely:

> The first aspect: It relates to the components, quality and degree of severity of the body’s immune system reactions with viral infection, and the quality and severity of the effects of those immune reactions on the extent of the stability and harm of the patient’s health status.

> The second aspect: it relates to the pathological characteristics of the viruses themselves, in each type, to target the cells of certain organs in the body without others, and the methodology of their pathogenic behaviors in dealing with the body’s organs. That is, the amount of “viral load” that succeeded in entering the body and causing the viral disease, the characteristics of the disease mechanism (disease mechanisms) resulting from it, the severity of the “virulence” (virulence), and the organs that prefer to attack it (Virus Tropism).

> The third aspect: It consists of two parts, the first: the extent to which this viral disease causes complications that allow another bacterial infection to begin to cause more harm to the person’s body. And second, the severity of the functional impairment of some important members of the body and the pathological signs resulting from that, whether that functional damage was rapidly emerging or chronic over time.

Immune system interactions

According to the British Society for Immunology, that there are several pathways for the reactions of the body’s immune system with the occurrence of viral infection.

The first is through the use of cytotoxic cells and the chemical compounds that use them.

The second is through the use of interferons.

And the third is through the use of antibodies.

The complex explains the path of the first path by saying what is summarized: When the virus infects a person, it enters into host cells in his body in order to survive and reproduce. Once the viruses enter the host cells, they disappear from the body’s immune cells. Consequently, immune system cells cannot “see” the virus and cannot know at that time that the host cell has become a virus-infected cell (Virally-Infected Cell). To overcome this, the host cells reveal what is inside them to other cells (immune cells) by using a special system of chemical compounds that specialize in providing that service. That is, it is a chemical system that allows cells infected with viruses to make other cells know what foreign particles are inside them. These specialized chemical compounds are called the MHC class I.

Killer cells. The mechanism for this is that the host cell displays on its surface protein fragments that contain parts of the components of what is inside it. And in the event that there are viruses inside, those protein pieces will contain parts of the virus’s proteins. And then the immune system cells (especially the T cells) will notice and distinguish those viral parts, which will appear on the surface of the cell as stimulating lights that are different in color from the host cell’s proteins, and thus the immune T cells know that there are viruses inside those host cells.

And T cells have the immune capabilities to recognize and observe microbes, and roam the body all the time in search of any microbial infection, viral or bacterial or other. Among them is the type of “cytotoxic T cells”, whose mission is to eliminate the host cells that contain viruses inside them, by using cytotoxic chemicals, thus preventing the survival of invasive viruses.

Because viruses have high evasion and adaptation capabilities, they have developed ways to avoid being detected by T cells. One way is to prevent the histocompatibility complex proteins from reaching the cell surface to display bits of viral proteins. If this happens, the T cell does not know that there is a virus inside the infected cell.

On the other hand, the body’s immune system has another ability to recognize and deal with this matter. Specifically, there are immune cells called “natural killer cells”, which have the ability to notice that there are cells that display “a little” of “tissue compatibility complex” proteins on their outer surface, and realize that this is due to the presence of elusive viruses inside, and at that time. Toxic chemicals are released in a manner similar to the action of “killer T cells” to destroy the host cell containing viruses.

As with any means of defense, killer immune cells (T cells and natural killer cells) are armed with “preformed mediators”, and “toxic chemicals” (cytotoxic factors) are stored in “granules” form. One of the “pre-fabricated media” is the compounds of Perforin, which pierce holes in cell membranes, allowing “toxic chemicals” to be released from the granules and their entry into the cell containing viruses. In their fusion with the virus-containing cell, the killer immune cells do two more things. The first is to stimulate nearby immune cells to participate in the process of eliminating virus-containing cells, and the second is to produce new protein substances, the most important of which are cytokines.

Immune proteins

> interferons. In the second pathway, virus-infected cells produce and release small proteins called interferons, as a means of immune protection against viruses. And interferons work to prevent the reproduction of viruses, by directly interfering with their ability to multiply inside the infected cell. At the same time, interferons also act as signaling molecules that allow infected cells to warn cells close to the viral presence within them, which causes neighboring cells to send in for help by increasing the placement of complex histocompatibility proteins on their surface (as previously explained), so that immune cells can “T” (Who scans the area) to pay attention, and work to identify and eliminate viral infection as described above.

Antibodies. In the third pathway, antibodies are used, which neutralize the capabilities of viruses before they have a chance to infect the cell. Antibodies are proteins that recognize and bind to viruses that precede them by attaching to them. This linking serves many purposes in the mechanisms of eliminating the virus:

– The first mechanism: the antibodies neutralize the capabilities of the virus, which means that it is no longer able to infect the host cell.

– The second mechanism: Many antibodies can work together to stick to a large number of viruses in a process called Agglutination, and thus make these accumulating viruses an easy target for immune cells to eliminate them instead of a large number of single and spread viruses.

– The third mechanism: To eradicate viruses, antibodies activate phagocytes. This is done by attaching the antibody (attached to the virus) to the surface of the phagocytic cells, starting the process of engulfing them together (Phagocytosis), and then destroying the viruses inside that phagocyte.

– The fourth mechanism: the antibodies work to destroy the lipid envelope surrounding the virus, that is, it is more like the action of soap and water in destroying the fat-coated viruses.

Satisfactory repercussions and

as a result of the pathways of these immune reactions, we note the following results:

First: the severity of the disease. The severity of the occurrence of “viral disease” may itself depend on general factors in the body of the infected person (Host Factors) related to the efficiency of the immune system. Among these factors: advancing age, being young, or having accompanying chronic diseases such as diabetes, high blood pressure, heart disease or cancer, or temporary health conditions such as pregnancy, or during the recovery period from treatments for cancerous diseases. In addition to genetic factors, the quality of nutrition, the extent of physical exercise, and the degree of psychological comfort.

Second: a harmful immune reaction. It is very possible that the quality of the reactions and the response of the body’s immune system to the viral infection is the main reason for the occurrence of a disease of varying severity in its symptoms and pathology, and also in repercussions that may reach damage to a number of body organs. It is described by medical sources as “pathological immune disorders due to viral infection” (Virus-Induced Immunopathology).

Specifically, the excessive secretion of cytokines and interferons and the production of antibodies, and the overactivity of T cells, all or some of them, may have uncontrolled pathological repercussions on the whole body and threaten the stability of the state of health in it, as well as on the coherence of the functional performance of several members in The body such as the lungs, liver, kidneys, and the circulatory system. To clarify, for example, the excessive secretion of cytokines, as a result of the lack of discipline of the intensity of the reaction of the body’s immune system, may cause a number of repercussions within what is medically called “cytokine release syndrome”. And in it, a general state of deterioration occurs in the body as a result of an immune reaction that exceeds the need. Among its symptoms are: low blood pressure, high body temperature, fatigue, muscle and joint pain, vomiting, diarrhea, rash, and mental confusion. Most importantly, the immune cells attack the tissues and cells of the lungs and cause damage and the accumulation of fluid in the lungs.


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