"Pathogenic microorganisms." . . . . . . . . "There are a multitude of pathogens capable of infecting the human body and causing disease. This program explores the six main categories of pathogens: bacteria, viruses, fungi, protozoa, prions and macroparasites. Their structure, mode of transmission, and the changes they cause in the host are described." . "Pathogens and infectious disease" . "Communicable diseases." . . . . "Infection." . .