A disease is simply a specific abnormal condition that negatively affects the functionality or structure of a part or all of an organ, and this is not caused by any direct external injury to the organism. Most diseases are often understood to be associated with specific anatomical symptoms and signs. For example, diabetes is usually perceived as a metabolic disorder, in which glucose concentrations are higher than normal. However, while glucose concentrations can be a result of insulin production, they also can be a result of a high-fat diet, smoking, or other non-insulin-producing factors.
Every disease has a pathophysiological and immunological mechanism, which means that it has a certain area of the organism which becomes abnormal and in turn causes disease. The term pathological or pathophysiological indicates that the abnormality is beyond cure. Immunologically, pathogens can only gain immunity if the invading organisms are killed. Therefore, once an organism has become pathophysiological, it cannot normally recover. This is why diseases have both Pathophysiological and Immunopathologic aspects.
All diseases have a cause, such as infection with a virus or bacteria or a tissue damaged by the same virus or bacteria. In most of these cases, the causative agent is known. The virus or bacteria need to invade and infect a target organ before it spreads to the rest of the body. Some infectious agents have genetic material within their code that enables them to enter target tissues without being transmitted to other parts of the body. Examples of such agent include fungi, bacteria and parasites.
Pathophysiological causes of diseases are generally known and understood. This means that the organisms involved cannot survive in their normal environment. They may become pathophysiological when the organism comes into contact with an infectious agent. Such organisms will then start to grow faster and gain energy to move towards the bloodstream. When they get there, they start to reproduce. This process may continue until they have reached the point that they can no longer sustain their existence without help from something else.
Immunopathologic causes of infectious diseases are generally not known. But what we do know is that the organisms involved are unable to live in their normal environment. To compensate for this, the organisms develop immunity to the disease or infection. This means that once they come into contact with an infectious agent, they are unable to pass on the infection to others because the immune system has already developed an immunity to it.
Immunopathologic causes of infectious diseases occur when the normal functions of the immune system are impaired. The immune system is the part of the body that recognizes and fights infections. Once the normal functions of the immune system are compromised, the normal functions of other organs in the body also become compromised. The result is that the body is unable to fight off infections and as a result the organisms involved may become pathophysiological.