pesti-, pest- +

(Latin: plague, contagion)

pestis major
Bubonic plague or pneumonic plague; the typical sever form of plague.
pestis minor (s) (noun) pestis minors (pl)
A form of the virulent disease in which a person is able to walk around: A pestis minor is an ambulatory plague or a mild form of bubonic plague that is characterized by less serious symptoms; such as, a mild fever and lymphadenitis (inflammation of lymph nodes, organs that fight infections).
The study of pests.