Introduction To Viruses PDF

Introduction to Viruses Read Chapter 13  Significance of Viruses Viruses most abundant “life form” on planet All living organisms infected by viruses Important in global nutrient cycling – Control dynamics of organisms Outnumber Bacteria in environment by 10 to 100 fold E...

Introduction to Viruses Read Chapter 13  Significance of Viruses Viruses most abundant “life form” on planet All living organisms infected by viruses Important in global nutrient cycling – Control dynamics of organisms Outnumber Bacteria in environment by 10 to 100 fold Especially prominent in aquatic ecosystems – Marine – Freshwater May be equally abundant in soil  Term Virus Generally applied Latin for “poison or poisonous slime” In early medical literature for any infectious disease Viruses were referred to as “Filterable Agents” Could not be proved with Koch’s Postulates Later Term “Virus” Restricted to these Filterable agents – Bacteria could be seen and Koch’s Postulates applied, not so with virus  Viruses General Description – Virion - extracellular small particle containing a nucleic acid and surrounded by protein aka virus particle – Obligate Intracellular pathogen – Virus replication New nucleic acid New protein coats Known as viral infection – Host is cell in which virus can replicate  Virus definition Small infectious particles Covering on outside – Capsid – (Sometimes with envelope) Central Core – Genetic Material – (sometimes with proteins or enzymes)  Principles of Virus Taxonomy lack of information on origin and evolutionary history makes viral classification difficult a uniform classification system was developed in 1971 by the International Committee for Taxonomy of Viruses (ICTV) – in most current report described ~2,000 viruses – classification based on numerous characteristics most important – nature of genome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6  Viral Genomes, Baltimore Classification  Viral Taxonomy Family names end in -viridae. Genus names end in -virus. Viral species: A group of viruses sharing the similar genetic information and ecological niche (host). Common names are used for species. Subspecies are designated by a number.  Viral Taxonomy Examples Herpesviridae Retroviridae (Family) Herpesvirus Lentivirus (Genus) Human Humanherpes virus immunodeficiency virus HIV-1, HIV-2 HHV-1, HHV-2, HHV-3 Coronaviridae Betacoronavirus SARS coronavirus 2 Basic Virus structure  Viral Structure Capsid – Coat, shell – Made up of protein subunits called capsomeres – Self-assemble into capsid Helical polygonal (icosahedron, 20 sided) Filamentous Complex  Virus capsid – Protects Surrounds genome of virus – Transport Has receptor Proteins often “spikes” Binds to host – Deliver Helps eject viral genome – Especially in complex viruses Cell Mol Life Sci. 2007 Jun; 64(12): 1484–1497  Viral Structure (cont) Envelope – membranous structure surrounds capsid – Viral envelope is a lipid bilayer embedded with glycoproteins – Often this membrane is derived from the host cell membrane as virus leaves the cell. – Plays important role in host recognition or specificity  Tobacco Mosaic Virus Simple RNA Virus Virion – Helical cylinder – Protein Capsid – Capsid made up of Capsomeres Infects Solanaceous plants such as tobacco and tomato Human Papilloma Virus icosohedral  Ebola Virus Created by CDC microbiologist Charles Humphrey, this negatively- stained transmission electron micrograph (TEM) revealed some of the ultrastructural curvilinear morphologic features displayed by the Ebola virus discovered from the Ivory Coast of Africa.  Virus types Simple viruses - capsule and genetic material Complex - virus has many appendages – Many are Bacteriophage – Multiple parts that must be assembled to allow it become infectious Complex Viruses Figure 13.5a  Viruses Types Naked or Enveloped Capsids – Helical or filamentous Rabies and Ebola – Polyhedral Adenovirus and Polio Virus Influenza or herpes virus Complex – Bacteriophage  Summarize Share with your neighbor the basic structure of a virus – What are the major components? Capsid Genome Envelope – How are they assembled? – What it the difference between simple and complex viruses  Obligate intracellular Parasite Viruses must be grown in living cells. – Bacteriophages form plaques on a lawn of bacteria. Figure 13.6  Growing Viruses Animal viruses may be grown in living animals, cell cultures or in embryonated eggs. Figure 13.7  Virus Identification Plaque assays Cytopathic effects Serological tests – Detect antibodies against viruses in a patient. – Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot. Antigen tests Nucleic acids –NAAT test – Molecular diagnostic tests – PCR, rtPCR http://upendrats.blogspot.com/2010/03/cultivation-of-viruses.html  Human Cell CPE Jundishapur J Microbiol. 2014 June; 7(6): e10375. Virus Identification Figure 13.9  Cytopathic Effect Respiratory syntytial Virus (RSV)  HPV and Pap smear Crook, Tim & Farthing, A. (2002). Human papillomavirus and cervical cancer. British journal of hospital medicine. 49. 131-2.  Next Time Viral Life Cycles and more!