Agent is that that acts, that operates or acts, is what practices the action.
The word agent has different definitions depending on the approach in which it is used. Ex.: A chemical agent is the body that causes a reaction on the other. Administrative agent is that person in charge of someone else's business, is the intermediary – insurance agent, real estate agent, etc. Public agent is the prosecutor, the delegate, the prosecutor and the police officer.
liability agent
Agent of the passive is the complement of the sentence constituted by the agent of the verbal action in the passive voice, that is, the one who practices the action suffered or received by the subject. It is usually introduced by a preposition. E.g.: The daughter is educated by the mother.
Etiological agent
It is the organism that causes a disease, which can be a virus, a bacterium, a fungus, a protozoan, etc. The term is used in Parasitology to designate a causative agent of a disease. E.g.: Chagas disease, in which the causative agent is Trypanosoma cruzi.
infectious agent
Infectious agent is an agent that causes infections, which enter the body through viruses, bacteria, etc., which overcome the body's natural barriers. They penetrate through saliva, breath, placenta, etc. E.g.: flu.