A bug is an illness which is caused by small organisms such as bacteria.
(由细菌引起的) 疾病 • I think I've got a bit of a stomach bug. 我觉得我有点肠胃感染。
If someone bugs a place, they hide tiny microphones in it that transmit what people are saying.
(在某处) 装窃听器 • He heard that they were planning to bug his office.