Biological agents include bacteria, viruses, fungi, other microorganisms and their associated toxins.
They have the ability to adversely affect human health in a variety of ways, ranging from relatively mild, allergic reactions to serious medical conditions, even death.
These organisms are widespread in the natural environment; they are found in water, soil, plants, and animals.
Because many microbes reproduce rapidly and require minimal resources for survival, they are a potential danger in a wide variety of occupational settings.
Source:OSHA(https://www.osha.gov/SLTC/biologicalagents/index.html (link is external))