Infectious Diseases Ch 28 Infectious Diseases Matching Vocabulary Tools A B Bacteria single cell organism, live almost anywhere, found in air, soil, water, produce poisons that are harmful to humans. Viruses smallest known type of infectious agents Rickettsias like a bacteria however multiply like a virus Protozoan most are harmless, 30 cause disease to the human body, found in poor sanitation and tropical areas. Fungi make their own food, feed off dead animals, insects, and leaves. Live in dark, damp environment. In the body, found in hair (ringworm), nails and skin (athletes foot).