Products, compositions, systems, and methods for treating a subject carrying a virus or bacterium. The methods may be performed in situ in a non-invasive manner by application of an initiation energy to the subject thus producing an effect on or change to a target structure of the subject directly or indirectly. The methods may further be performed by application of an initiation energy to a subject to activate within the subject a photoactivatable drug directly or indirectly, optionally in the presence of one or more plasmonics active agents, thus treating the virus or bacterium. Also provided are kits containing products or compositions formulated or configured and systems for use in practicing these methods.