pathogen vs infectious agent

pathogen and infectious agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
pathogen	Yes	No	No	No
infectious agent	Yes	No	No	No

As nouns, infectious agent is a hypernym of pathogen; that is, infectious agent is a word with a broader meaning than pathogen:

pathogen: any disease-producing agent (especially a virus or bacterium or other microorganism)
infectious agent: an agent capable of producing infection

Other hypernyms of pathogen include micro-organism, microorganism, infective agent.

pathogen (noun)	infectious agent (noun)
any disease-producing agent (especially a virus or bacterium or other microorganism)	an agent capable of producing infection