Pathogens (pathogens) are organisms such as protozoa, bacteria, and viruses that parasitize living organisms and cause diseases. Among the parasitic organisms, those that are particularly pathogenic.
Diseases caused by pathogens are called infectious diseases.
In order to understand the concept of pathogens and determine what is pathogens and what is not, it is necessary to understand the phenomenon of parasitism and the complex concept of pathogenicity. Parasitism is a phenomenon in which one organism (in this case, a microorganism) lives by utilizing the mechanism of the body of the other organism. Looking at such a parasitic phenomenon from the host side (parasitic side), most of the parasites that enter the body are so-called "harmful organisms" and pathogenic microorganisms, and in that case, " It is called a "pathogen". However, in some cases the parasite is not pathogenic, in which case the parasite is not a "pathogen", that is, whether a parasite is a "pathogen" or not, is it pathogenic? It depends on the judgment.
Pathogenicity means the ability to cause a disease, but the term is complex and it is not always easy to determine whether a microorganism is pathogenic or not.
Explain why the determination of pathogenicity, which is the basis for determining whether or not it is a pathogen, is complicated. The degree to which a parasite grows in the host is affected by the balance between growth-promoting factors and growth-suppressing factors in a kind of environment called the host. The growth-promoting factor is the presence of nutrients required by the parasite, the affinity between the parasite and the host, and the like, and the growth-suppressing factor is a self-defense mechanism such as the immune system of the host. These factors vary considerably depending on whether the host is a plant or an animal, and for that matter, they vary from species to species. Whether or not a disease develops depends on the correlation between the pathogen and the host and the relative relationship (relationship between microbial species and organisms, and the relationship between microbial species and individual organisms). In this way, the determination of pathogenicity is complicated.
To complicate matters, pathogenicity is often regarded as a general attribute or characteristic of microorganisms by species, but this is not always the case, and the subtle differences between microorganisms that fall into the same species. There is a complexity that there is a difference in the virulence virulence and the virulence (pathogenicity) of each of them even if they are compared one by one (for example, even if the mutant species and the mutant species are compared).
Pathogens have the following characteristics.
Pathogens are invisible (to the naked eye and from the patient's appearance).
When a pathogen of a certain disease acts on a healthy human, the disease develops. The disease does not develop in humans who are not affected by the pathogen. (Responsible factor for disease onset: necessary and sufficient condition)
It can be transmitted from a sick patient to another person by several routes, such as direct contact or via the air, to develop the disease (contagious).
Since the transmission increases the number of patients (who should have the pathogen), the pathogen itself also has the property of increasing (proliferative).
When a patient with an infectious disease moves to another location, a new infectious disease develops at that location (portable).
In humans and animals, pathogens are among microorganisms such as viruses, eubacteria, fungi, and protozoa.