In epidemiology, transmission refers to the mechanism by which a pathogen enters the host. A pathogen is a harmful microorganism (e.g., bacteria, viruses) capable of causing illness to a susceptible host.
In this case, the missing word indicates 'A mode of TRANSMISSION from the source to the host'.
The different types of transmission include:
Direct contact transmission (e.g., touching, kissing), which triggers the transference of the pathogen to a susceptible host.
Aerosol transmission (airborne transmission): characterized by the inhalation of small particles (aerosol droplets) exhaled by an infected host.
Zoonotic transmission: the reservoir is an infected animal.
Oral transmission: infections caused by direct ingestion of the pathogen.
Vector-borne transmission: infections transmitted by different animals (i.e., vectors) such as mosquitoes, ticks, fleas, etc.
