It is important that before entering fully into the meaning of the term etiological agent, we proceed to know the etymological origin of the two words that give it form:
-Agent is a word that derives from Latin, specifically, from “agentis” that can translate as “he who takes action.” It is the result of the sum of two different parts: the verb “agere”, which is equivalent to “act”, and the suffix “-nte”, which is used to indicate the person responsible for the action.
-Etiological, on the other hand, comes from the Greek, exactly from the term “aitology”, which is made up of three different parts: the noun “aitia”, which means “cause”; the noun “logos”, which can be translated as “study”; and the suffix “-ia”, which is used to indicate “quality”.
The concept of agent refers to that or that which has the capacity to produce something or to act. Etiological is what is linked to the etiology: the analysis of the causes or origins of things or diseases.
With these ideas clear, we can advance in the DEFINITION OF an etiological agent. It is the element that promotes the development of a disease. Bacteria and viruses are among the most common etiologic agents.
Take the case of rabies. This is a contagious and viral disease that attacks the central nervous system (CNS). Once the animal or the person contracts rabies, they begin to suffer various disorders, such as paralysis, hyperactivity and aggressive tendencies, until they enter a coma and, generally, die due to cardiorespiratory arrest or infection derived from the big picture. The cause of this disease is a virus, known simply as the rabies virus. Therefore, it can be said that the rabies virus is the etiological agent that causes this contagious and generally fatal disease.
Said virus is the etiological agent since it drives the development of the disease. In other words: without the infection of the organism by the rabies virus, the irruption of rabies is not possible. That is why this virus is defined as an etiological agent, because it is the origin or cause of the disease. The same is true for other viruses that cause other disorders.
Another example would be the pathology called Hemolytic Uremic Syndrome (HUS), which can be caused by a wide variety of infectious pictures, of etiological agents, such as Shigella dysenteriae type1, Salmonella typhi, Streptococcus pneumoniae or Campylobacter jejuni.
In meningitis, on the other hand, the most frequent etiological agents are gram-negative bacteria, S Pneumoniae or listeria monocytogenes, for example.
Of course, it should not be overlooked that one of the best-known agents of this type is the one considered to cause AIDS. We are referring to the Human Immunodeficiency Virus (HIV), which is part of the retrovirus family and can be of two types: HIV 1 and HIV 2.