How pathogens invade the body, how new infectious diseases are recognized, how epidemics arise and how new treatments are developed are discussed in this Howard Hughes Medical Institute1999 Holiday Lectures on Science Series. Donald E. Gamen explains the relationship between Kaposi’s sarcoma and AIDS, showing how microbiology identifies an infectious organism, in "Microbe Hunters: Tracking Infectious Agents". Then B. Brett Finlay, in "The Microbes Strike Back", discusses how bacteri a spread, how antibiotics do - and don’t - work, superbugs and pathogenomics. Study guide available. Closed captioned.