The Single Biggest Threat to Man's Continued Dominance on the Planet is a Virus | HSCI 4770, Study notes of Virology

Download The Single Biggest Threat to Man's Continued Dominance on the Planet is a Virus | HSCI 4770 and more Study notes Virology in PDF only on Docsity! “The single biggest threat to man’s continued dominance on the planet is a virus.” -Joshua Lederberg “Viruses are a piece of bad news wrapped up in a protein” - Sir Peter Medawar "Nothing brings us so close to the riddle of Life - and its solution - as viruses."  - Wolfhard Weidel Virology Introduction Chapter 1 Impact of viruses • Leading source of genetic innovation – “invent” new genes – transfer genetic material among organisms • Viruses cause 15% cancers • Regulate saltwater & freshwater ecosystems • Used as molecular biology tools to study host-cell processes – replication, transcription & translation, etc. • Bacteriophages may be used in clinically to treat bacterial infections. • Gene therapy – may be used to deliver genes into host cells • First vaccine (smallpox) proved we could prevent infections Theories of Viral Origin Uncertain -nobody knows There may be multiple origins. There is no fossil record of viruses. outer space? 1. Regressive theory – viruses were once intracellular parasites that lost their essential genes required for replication and maintenance 2. Cellular origin theory – viruses arose from cellular nucleic acid that evolved to replicate independently of the host genome 3. Co-evolution theory – viruses and cells coevolved from complex polymers of nuclei acids. Some life forms became viruses, others became cells Where did viruses come from? (a) (b) (c) From free-living From host-cell From complex organisms genome polymers (coevolution with cellular life forms) Cell Cell Pool of nucleotides Polynucleotides Self-replicating RNAs Move into, a cell 1 Pool of RNA, DNA, proteins, lipids, carbohydrates Bacterial DNA Free-living genome bacterium Coevolution std MBNA) ~) < Move into acell | Progressive loss of bacterial genetic information and functions Virus genome All three theories yield both cellular life forms (hosts) and viruses (obligate intracellular parasites) 3 problems every virus must solve 1. How to reproduce within a cell 2. How to spread to a new host 3. How to evade host defenses • The diseases viruses cause are determined by the ways a virus solves these problems. 1. Reproduce • copy genetic information, produce mRNA, get components made & assembled • Most cells are not actively dividing. Virus has to turn on DNA replication machinery or bring in its own. • RNA viruses have to encode RNA-dependent RNA polymerase, sometimes called transcriptase 2. Spread • Transmission – coughing, eating, sex • There are ~200 different types of cells in the body. • A given virus will be able to infect only a few of these (target tissue). • If a virus reproduces so efficiently that it kills its host before it has a chance to infect another host, the virus will not make it. Viruses in History: Great Epidemics • Influenza • Poliomyelitis • Acquired Immunodeficiency Syndrome (AIDS) Figure 1.14a: FDR at Warm Springs, Georgia, in 1924. Figure 1.14b: The press portrayed Roosevelt as a robust, strong leader. Recent Viral Outbreaks • Hantavirus: Four Corners Disease - 1993 • West Nile Virus (WNV), New York City - 1999 • Norovirus outbreaks (cruiseships) • Foot and Mouth Disease, United Kingdom - 2001, 2007 • SARS - 2003 • Influenza H5N1 (avian flu) – 1997 • Influenza H1N1 (swine flu) –2009