which item must be passed from person to person in order to acquire an infectious disease?\no…

Brief Explanations:

Infectious diseases are caused by pathogens. For a person to acquire an infectious disease, the pathogen (disease - causing agent like bacteria, viruses, etc.) must be transmitted from an infected person (or source) to a susceptible person. Blood and saliva can be vehicles for pathogen transmission in some cases (e.g., blood - borne pathogens like HIV, or saliva - transmitted viruses like Epstein - Barr virus in some situations), but they are not the essential item. An antigen is a molecule that can trigger an immune response, but it is not the entity that causes the disease (the pathogen is).

Answer:

pathogen