Pathogen Posted on 13th December 20157th April 2022 by ThePD (The Project Definition) Pathogen is a microorganism that causes infectious disease. Bacteria and viruses are the main pathogens. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in HSE and tagged health. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.