Six links in chain of infection

Portal of entry

Fifth stage; route through is the pathogen enters it's new host. It could inhale it, ingest it, or sexual contact

Infectious agent

First stage; pathogen

Route of transmission

Fourth stage; Method by with pathogen gets from reservoir to new host from touching the air

Reservoir host

Second stage; place or host where the pathogen lives/resides

Susceptible host

Sixth stage;Organism that excepts pathogen; back to beginning

Portal of exit

Third stage; route of escape of the pathogen from the reservoir