Immortal pathogens include bacteria, viruses, and parasites, which are intracellular or parasitic, and difficult to eradicate.  Immortal pathogens cause acute illness and thereafter persist as chronic infections; and a person does not acquire immunity to the pathogens.  The person develops reduced immune function, as immortal bacteria infect white blood cells and spread chronic infections.  The immortal pathogens spread, unrecognized, for months, years, or decades, until the chronic infection evolves into a chronic disease.