epidemiologist
A specialist who studies the patterns, causes, and effects of health and disease conditions in defined populations.
He is an epidemiologist who studies infectious diseases.
Epidemiologists are investigating how the new virus spreads.
Compound of 疫 (えき, 'epidemic') + 学 (がく, 'study') + 者 (しゃ, 'person'). The term is a straightforward Sino-Japanese formation.