Historical Highlights 1798 Smallpox vaccine developed Edward Jenner – vaccination vs variolation – Why did this work at all? Last case of natural smallpox infection was in 1977 – (have been lab accidents) Success of vaccine campaign due to: – lack of animal reservoir for virus – good, stable attenuated live vaccine

Historical Highlights 1898Viruses recognized as agents responsible for plant (TMV) and animal disease (FMDV). – Previously knew about bacteria and fungi (could grow these) as disease agents, but hard to break this dogma. – Viruses shown to pass through porcelain candle filters. – Definitely multiplied in suitable host, but never without. New type of organism (not a toxin)

Historical Highlights 1911 A virus causing sarcomas in chickens identified – Rous sarcoma virus 1915 Discovery of bacteriophages (bacteria "eaters") – TMV recognized to be protein + nucleic acid. – Had assay for TMV. – Purified and shown to contain constant amount of phosphorous (nucleic acid).

Historical Highlights 1939 A virus (TMV) visualized by electron microscope.

Historical Highlights 1949Human cell cultures developed for growth of polio virus.

Historical Highlights 1952DNA of a bacteriophage shown to be infectious. Hershey & Chase expt. DNA = genetic material

Historical Highlights 1957Interferon discovered. Infectivity of TMV RNA discovered (RNA genetic material)

Historical Highlights 1962Icosahedral symmetry of isometric viruses discovered