The phrase "etiological agent" refers to a specific thing, usually a microorganism or substance, that causes a disease or condition. It is the root cause or source of the problem. Full definition
Rotaviruses are the most important etiological agent of acute gastroenteritis in young children worldwide. (jcvi.org)
Given the clear link to croplands / agricultural soils indicated by a variety of our results at a time and in a region where the ground is frozen throughout the high KD season, a whole range of new possibilities emerges regarding the nature of the KD etiological agent. (pnas.org)