Epidemiology, literally meaning “the study of what is upon the people”, is derived from Greek epi, meaning ‘upon, among’, demos, meaning ‘people, district’, and logos, meaning ‘study, word, discourse’, suggesting that it applies only to human populations. However, the term is widely used in studies of zoological populations (veterinary epidemiology), although the term “epizoology” is available, and it has also been applied to studies of plant populations (botanical or plant disease epidemiology). The distinction between “epidemic” and “endemic” was first drawn by Hippocrates, to distinguish between diseases that are “visited upon” a population (epidemic) from those that “reside within” a population (endemic).
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