Translations:Basic Field Epi: Course Resource Book/152/en
Agent refers to the particular infectious agent that is a cause of the disease: virus, bacteria, fungus, parasite, or other microbe.
Different strains of the same bacteria or virus may either produce no disease or more severe disease. There are many different infectious agents and different sub-types or strains, these may all have different abilities to cause disease. Sometimes non-infectious causes are classified as agents for example lead as the agent that can cause lead poisoning or a plant toxin that can cause a type of plant poisoning.