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Fenner’s Veterinary Virology Fenner’s Veterinary Virology Fifth Edition Edited by Associate Editors: N. James MacLachlan, Stephen W. Barthold, DVM, PhD, BVSc, PhD, Dip ACVP Dip ACVP Distinguished Professor Distinguished Professor Emeritus Department of Pathology, Department of Pathology, Microbiology and Microbiology and Immunology Immunology School of Veterinary Medicine School of Veterinary Medicine University of California, University of California Davis, California, USA Davis, California, USA and David E. Swayne, DVM, PhD, Dip ACVP, Dip ACPV Extraordinary Professor Department of Veterinary Tropical Diseases Center Director Faculty of Veterinary Science USDA/Agricultural Research Services University of Pretoria Exotic and Emerging Avian Viral Diseases Onderstepoort, Republic of South Africa Research Unit Southeast Poultry Research Laboratory Edward J. Dubovi, Athens, Georgia, USA MS, PhD, Dip ACVM (Hon) James R. Winton, BA, PhD Director, Virology Section Animal Health Diagnostic Center Chief, Fish Health Section Department of Population Medicine United States Geological Survey and Diagnostic Sciences Western Fisheries Research Center College of Veterinary Medicine Seattle, Washington, USA Cornell University Ithaca, New York, USA AMSTERDAM(cid:129)BOSTON(cid:129)HEIDELBERG(cid:129)LONDON(cid:129)NEWYORK(cid:129)OXFORD(cid:129)PARIS SANDIEGO(cid:129)SANFRANCISCO(cid:129)SINGAPORE(cid:129)SYDNEY(cid:129)TOKYO AcademicPressisanimprintofElsevier AcademicPressisanimprintofElsevier 125LondonWall,LondonEC2Y5AS,UnitedKingdom 525BStreet,Suite1800,SanDiego,CA92101-4495,UnitedStates 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom Copyrightr2017,2011,1999ElsevierInc.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronicormechanical,includingphotocopying, recording,oranyinformationstorageandretrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseekpermission, furtherinformationaboutthePublisher’spermissionspoliciesandourarrangementswithorganizationssuchastheCopyrightClearanceCenterand theCopyrightLicensingAgency,canbefoundatourwebsite:www.elsevier.com/permissions. ThisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythePublisher(otherthanasmaybenotedherein). Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperiencebroadenourunderstanding,changesinresearch methods,professionalpractices,ormedicaltreatmentmaybecomenecessary. Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluatingandusinganyinformation,methods,compounds, orexperimentsdescribedherein.Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers,including partiesforwhomtheyhaveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeanyliabilityforanyinjuryand/ordamageto personsorpropertyasamatterofproductsliability,negligenceorotherwise,orfromanyuseoroperationofanymethods,products,instructions, orideascontainedinthematerialherein. BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress ISBN:978-0-12-800946-8 ForInformationonallAcademicPresspublications visitourwebsiteathttps://www.elsevier.com Publisher:SaraTenney AcquisitionEditor:LindaVerteeg-Buschman EditorialProjectManager:MaryPreap ProductionProjectManager:JuliaHaynes Designer:MattLimbert TypesetbyMPSLimited,Chennai,India Dedication We recognize the remarkable accomplishment that was the global eradication of rinderpest, long a scourge of animal production systems in much of the world. The global eradication of rinderpest in 2011 represents only the second time a pathogen has been eradicated from the planet through concerted human effort, and serves as an inspirational example of the constructive potential benefits of science to the entire global community. The collaborative efforts of academic institutions and governments along with animal health experts and vaccine delivery teams will hopefully provide the model for future disease eradication efforts. List of Contributors Udeni B.R. Balasuriya, BVSc, MS, PhD, Professor of Ruben O. Donis, MV, PhD, Deputy Director, Influenza Virology, Maxwell H. Gluck Equine Research Center, Division, Biomedical Advanced Research and Department of Veterinary Science, University of Development Authority (BARDA), Assistant Secretary Kentucky,Lexington,Kentucky,USA for Preparedness and Response, Department of Health ArteriviridaeandRoniviridae;Togaviridae;Flaviviridae andHumanServices,WashingtonDC,USA Orthomyxoviridae Simon Barratt-Boyes, BVSc, PhD, Professor, Department of Infectious Disease & Microbiology, Ian Gardner, BVSc, MPVM, PhD, Professor and Center for Vaccine Research, University of Pittsburgh, Canada Research Excellence Chair, Department of Pittsburgh,Pennsylvania,USA Health Management, Atlantic Veterinary College, AntiviralImmunityandVirusVaccines University of Prince Edward Island, Charlottetown, PrinceEdwardIsland,Canada Martin Beer, PhD, Institute of Diagnostic Virology, EpidemiologyandControlofViralDiseases Friedrich-Loeffler-Institut, Federal Research Institute forAnimalHealth,Su¨dufer,Greifswald,Germany James Gilkerson, BVSc, BSc(Vet), PhD, Professor, Bunyaviridae Faculty of Veterinary and Agricultural Science, The UniversityofMelbourne,Melbourne,Victoria,Australia Brian Bird, DVM, MSPH, PhD, Veterinary Medical Picornaviridae Officer, Viral Special Pathogens Branch, Centers for DiseaseControlandPrevention,Atlanta,Georgia,USA William T. Golde, PhD, Senior Scientist, Department of Arenaviridae Immunology, Plum Island Animal Disease Center, Agricultural Research Service, USDA, Orient Point, JoeBrownlie,BVSc,PhD,FRCVS,DipECVP, Emeritus USA Professor of Veterinary Pathology, Pathology and AntiviralImmunityandVirusVaccines Pathogen Biology, Royal Veterinary College, London, Carol Hartley, BSc(Hons), PhD, Senior Research Hertfordshire,UK Fellow, Faculty of Veterinary and Agricultural Science, Coronaviridae The University of Melbourne, Melbourne, Victoria, LarkL.Coffey,PhD, AssistantProfessor,Departmentof Australia Pathology, Microbiology and Immunology, School of Picornaviridae Veterinary Medicine, University of California, Davis, Hans Heidner, BS, MS, PhD, Professor, Department of California,USA Biology, University of Texas at San Antonio, San TheNatureofViruses Antonio,Texas,USA John M. Cullen, VMD, PhD, Dip ACVP, Professor, VirusReplication Population Health and Pathobiology, North Carolina State University College of Veterinary Medicine, Christine Herden, DVM, PhD, Dipl ECVP, Professor, Raleigh,NorthCarolina,USA Institute for Veterinary Pathology, Justus-Liebig- OtherViruses:Hepeviridae,Hepadnaviridae, Universita¨tGiessen,Giessen,Germany Delataviruses,Nodaviridae,andUnclassifiedViruses Bornaviridae Gustavo A. Delhon, DVM, MS, PhD, Associate Peter Kirkland, BVSc, PhD, Senior Principal Research Professor,SchoolofVeterinaryMedicine&Biomedical Scientist, Virology Laboratory, Elizabeth Macarthur Science, University of Nebraska-Lincoln, Lincoln, Agriculture Institute, Menangle, New South Wales, Nebraska,USA Australia Poxviridae Bunyaviridae xvii xviii ListofContributors Donald P. Knowles, DVM, PhD, Dip ACVP, Research John Parker, BVMS, PhD, Associate Professor, Baker Leader, USDA/Agricultural Research Services, Animal InstituteforAnimalHealth,DepartmentofMicrobiology Diseases Research Unit, Professor, Department of and Immunology, College of Veterinary Medicine, Veterinary Microbiology and Pathology, College of CornellUniversity,Ithaca,NewYork,USA Veterinary Medicine, Washington State University, CaliciviridaeandAstroviridae Pullman,Washington,USA Rhabdoviridae Colin R. Parrish, PhD, Professor of Virology, Baker InstituteforAnimalHealth,DepartmentofMicrobiology Xiang-Jin Meng, MD, MS, PhD, University and Immunology, College of Veterinary Medicine, Distinguished Professor, Department of Biomedical CornellUniversity,Ithaca,NewYork,USA Sciences and Pathobiology, Virginia-Maryland College Parvoviridae ofVeterinaryMedicine,Blacksburg,Virginia,USA CircoviridaeandAnelloviridae;OtherViruses: Patricia Pesavento, DVM, PhD, Dip ACVP, Professor, Hepeviridae,Hepadnaviridae,Delataviruses, Department of Pathology, Microbiology and Nodaviridae,andUnclassifiedViruses Immunology, School of Veterinary Medicine, John Munday, BVSc, PhD, Dip ACVP, Associate UniversityofCalifornia,Davis,California,USA Professor, Department of Pathobiology, Institute of PapillomaviridaeandPolyomaviridae;Caliciviridae Veterinary, Animal and Biomedical Sciences, Massey andAstroviridae University,PalmerstonNorth,NewZealand PapillomaviridaeandPolyomaviridae William Reisen, BS, MS, PhD, Emeritus Professor, Center for Vectorborne Diseases, Department of Brian Murphy, DVM, PhD, Dip ACVP, Associate Pathology, Microbiology and Immunology, School of Professor, Department of Pathology, Microbiology and Veterinary Medicine, University of California, Davis, Immunology,SchoolofVeterinaryMedicine,University California,USA ofCalifornia,Davis,California,USA Togaviridae;Flaviviridae Retroviridae Juergen A. Richt, DVM, PhD, Regents Distinguished Stefan Niewiesk, DVM, PhD, Dip ACVP, Professor, Professor, Department of Diagnostic Medicine/ Department of Veterinary Biosciences, The Ohio State Pathobiology, College of Veterinary Medicine, Kansas University,Columbus,Ohio,USA StateUniversity,Manhattan,Kansas,USA PathogenesisofViralInfectionsandDiseases Bornaviridae Michael Oglesbee, DVM, PhD, Dip ACVP, Professor Christina J. Sigurdson, DVM, PhD, Dip and Chair, Department of Veterinary Biosciences, The ACVP, Associate Professor, Department of Pathology, OhioStateUniversity,Columbus,Ohio,USA University of California, San Diego, School of PathogenesisofViralInfectionsandDiseases Medicine,LaJolla,California,USA Prions:AgentsofTransmissibleSpongiform Klaus Osterrieder, PhD, Professor, Managing Director, Encephalopathies Department of Veterinary Medicine, Institute of Virology,FreieUniversita¨tBerlin,Berlin,Germany Jonathan Towner, PhD, Lead, Virus Host Ecology Herpesvirales Section, Viral Special Pathogens Branch, Centers for DiseaseControlandPrevention,Atlanta,Georgia,USA Christopher Oura, BVetMed, MSc, PhD, Professor of Filoviridae Veterinary Virology, Department of Basic Veterinary Sciences, The School of Veterinary Medicine, The Veronika von Messling, DVM, PhD, Director and University of the West Indies, St Augustine, Trinidad andTobago Professor, Veterinary Medicine Division, Paul-Ehrlich- AsfarviridaeandIridoviridae Institut,Langen,Germany ParamyxoviridaeandPneumoviridae Massimo Palmarini, DVM, PhD, Professor, MRC- University of Glasgow Centre for Virus Research, Gary Whittaker, BSc, PhD, Professor, Department of Institute of Infection, Immunity and Inflammation, Microbiology and Immunology, College of Veterinary Glasgow,UK Medicine,CornellUniversity,Ithaca,NewYork,USA Reoviridae Coronaviridae Acknowledgements Murphy. The goal of this fifth edition of Veterinary Virology is to continue the agenda we began in the fourth edition, specifically to bring all aspects of veterinary and zoonotic virus diseases under a common umbrella. To that end, we gratefully acknowledge the Associate Editors of this text who contributed their spe- cialist expertise on virus diseases of laboratory animals, fish and aquatic species, and birds. We also gratefully acknowledgethe34contributorswhoacceptedtheonerous task of updating individual chapters. Lastly, we are espe- cially grateful to those individuals who, without recogni- In 1985, Frank Fenner (1914(cid:1)2010) had the idea to tion,agreedtoproofvariouschaptersandsectionsthereof, writeaveterinaryfocusedcompaniontothebook,Medical notably Drs.Kimberly Dodd,Kirsten Murphy, Linda Saif, Virology,whichheandDavidO.White(1931(cid:1)2004)had andDonalO’Toole,alongwiththosewhoprovidedfigures co-authoredin1970and1976.Thus,in1987,thefirstedi- includingDr.KevinKeelwhocontributedthepictureused tion of Veterinary Virology was published, with subse- onthecover. quent editionsin1993 and 1999.Other contributorstothe Asinprioreditions,weacknowledgeourfamilies,tea- firstthreeeditionsofthetextincludedPeterA.Bachmann chers, mentors and students for their inspiration and (1939(cid:1)1985),RudolfRott(1926(cid:1)2003),E.PaulJ.Gibbs, direction. Michael J.Studdert,MarianC.Horzinek andFrederickA. xix Chapter 1 The Nature of Viruses ChapterOutline Introduction:ABriefHistoryofAnimalVirology 3 ViralMembraneLipids 10 CharacteristicsofViruses 7 ViralMorphology 10 ChemicalCompositionoftheVirion 8 ViralTaxonomy 13 ViralNucleicAcidsintheVirion 8 PhylogeneticComparisonofVirusSequences 16 ViralProteinsintheVirion 9 INTRODUCTION: A BRIEF HISTORY OF early studies provided the essential operational definition of viruses as filterable agents. Chemical and physical ANIMAL VIROLOGY studies revealed the structural basis of viruses nearly 40 The history of human development has been shaped by at yearslater. least three major recurring elements: (1) environmental In the early 20th century, use of the filtration criteria changes; (2) human conflicts; (3) infectious diseases. led to the association of many acute animal diseases with Infectious diseases have impacted both humans and our what were later defined as viral infections: African horse food supply. The origins of veterinary medicine are sickness, fowl plague (high pathogenicity avian influenza), rooted in efforts to maintain the health of animals for rabies, canine distemper, equine infectious anemia, rinder- foodandfiberproduction,andanimals essential forwork- pest,andclassicalswinefever(hogcholera)(Table1.1).In related activities. Control ofanimal disease outbreaks was 1911, Rous discovered the first virus that could produce not possible until the pioneering work of the late 19th neoplasia (tumors), and for this discovery he was awarded century that linked microbes to specific diseases of plants a Nobel Prize. This early phase of virology was fraught and animals (see Murphy, F.A., 2012. The Foundations of with skepticism and uncertainty because of the limited Virology, for detailed discussion). Many attribute the tools available to study and characterize the filterable beginning of virology with the work of Ivanofsky and agents. Experiments using filters with varying retention Beijerinck on the transmission of tobacco mosaic virus. parameters demonstrated the existence of filterable agents Both scientists were able to demonstrate transmission of of different sizes. Some agents were inactivated with the agent causing disease in tobacco plants through filters organic solvents, whereas others were resistant. For equine that retained bacteria. Beijerinck also noted that the filter- infectious anemia, the acute and chronic forms of the dis- able agent could regain its “strength” from diluted mate- easewere perplexingand anunresolved conundrum.These rial, but only if it were put back into the tobacco plants. types of apparent inconsistencies made it difficult to estab- The concept of a replicating entity rather than a chemical lish a unifying conceptual description of the filterable or toxin had its genesis with these astute observations. agents. For research on animal diseases, early workers The era of veterinary virology had its beginning virtually were restricted to using animal inoculation in order to at the same time as Beijerinck was characterizing tobacco assess the impact of a treatment on any putative disease- mosaic virus transmission. Loeffler and Frosch applied causing agent. The logistics could be especially daunting the filtration criteria to a disease in cattle that later would forstudiesincattleandhorses.Helpinprovidingdefinition be known as foot and mouth disease. Repeated passage of tofilterable agents came fromthe discovery ofviruses that the filtrate into susceptible animals with the reproduction infectedbacteria.Twortin1915detectedtheexistenceofa of acute disease firmly established the “contagious” filterable agent that could kill bacteria. Like its plant and nature of the filtrate and provided more evidence for a animal counterparts, the strength of a dilute solution of the process that was inconsistent with toxic substances. These bacterial virus could be regained by inoculating new Fenner’sVeterinaryVirology.DOI:http://dx.doi.org/10.1016/B978-0-12-800946-8.00001-5 ©2017ElsevierInc.Allrightsreserved. 3 4 PART | I ThePrinciplesofVeterinaryandZoonoticVirology TABLE1.1 SelectedMomentsintheHistoryofVirology Year Investigator(s) Event Year Investigator(s) Event 1892 Ivanofsky Identificationoftobacco 1939 EllisandDelbruck One-stepgrowthcurve— mosaicvirusasfilterable bacteriophage agent 1946 Olafson,MacCallum,andFox Bovineviraldiarrheavirus 1898 LoefflerandFrosch Foot-and-mouthdisease 1948 Sanford,Earle,andLikely Cultureofisolated causedbyfilterableagent mammaliancells 1898 Sanarelli Myxomavirus 1952 DulbeccoandVogt Plaqueassayforfirstanimal 1900 Reed Yellowfevervirus virus—poliovirus 1900 McfadyeanandTheiler Africanhorsesicknessvirus 1956 Madin,York,andMcKercher Isolationofbovine herpesvirus1 1901 Centanni,Lode,andGruber Fowlplaguevirus(avian influenzavirus) 1957 IsaacsandLindemann Discoveryofinterferon 1902 NicolleandAdil-Bey Rinderpestvirus 1958 HorneandBrenner Developmentofnegative- stainelectronmicroscopy 1902 SpruellandTheiler Bluetonguevirus 1961 Becker Firstisolationofavian 1902 Aujeszky Pseudorabiesvirus influenzavirusfromwild 1903 RemlingerandRiffat-Bay Rabiesvirus birdreservoir 1903 DeSchweinitzandDorset Hogcholeravirus(classical 1963 PlummerandWaterson Equineabortionvirus 5 swinefevervirus) herpesvirus 1904 Carre´andValle´e Equineinfectiousanemia 1970 TeminandBaltimore Discoveryofreverse virus transcriptase 1905 Spreull Insecttransmissionof 1978 Carmichael,Appel,andScott Canineparvovirus2 bluetonguevirus 1979 WorldHealthOrganization WHOdeclaressmallpox 1905 Carre´ Caninedistempervirus eradicated 1908 EllermannandBang Avianleukemiavirus 1981 Pedersen Felinecoronavirus 1909 LandsteinerandPopper Poliovirus 1981 Baltimore Firstinfectiouscloneofan RNAvirus 1911 Rous Roussarcomavirus—first tumorvirus 1983 Montagnier,Barre-Sinoussi, Discoveryofhuman andGallo immunodeficiencyvirus 1915 Twortandd’Herelle Bacterialviruses 1987 Pedersen Felineimmunodeficiency 1917 d’Herelle Developmentoftheplaque virus assay 1991 WensvoortandTerpstra Isolationofporcine 1927 Doyle Newcastlediseasevirus reproductiveandrespiratory syndromevirus(PRRSV) 1928 VergeandChristofornoni Felineparvovirus(feline SeifriedandKrembs panleukopeniavirus) 1994 Murray Hendravirusisolated 1930 Green Foxencephalitis(canine 1999 WestNilevirusentersNorth adenovirus1) America 1931 Shope Swineinfluenzavirus 2002 Severeacuterespiratory syndromeoutbreak 1931 WoodruffandGoodpasture Embryonatedeggsforvirus propagation 2005 Palase,Garcia-Sastre, Reconstructionofthe1918 Tumpey,andTaubenberger pandemicinfluenzavirus 1933 DimmockandEdwards Viraletiologyforequine abortions 2008 Developmentofmolecular toolsandcomputersoftware 1933 Andrewes,Laidlaw,and Firstisolationofhuman for“nextgeneration Smith influenzavirus sequencing”and 1933 Shope Swinenaturalhostof metagenomicanalyses pseudorabies 2011 WorldOrganisationof Declarationoftheglobal 1933 BushnellandBrandly Avianbronchitisvirus AnimalHealth(OIE) eradicationofrinderpest 1935 Stanley Tobaccomosaicvirus(TMV) 2012 RecognitionofMiddleEast crystallized;proteinnature respiratorysyndrome ofvirusesconfirmed 2014 ReemergenceofEbolain 1938 Kausche,Ankuch,andRuska Firstelectronmicroscopy WestAfrica pictures—TMV TheNatureofViruses Chapter | 1 5 cultures of bacteria. Felix d’Herelle also noted the killing a human cell line was developed, and growth of poliovi- of bacteria by an agent that he called “bacteriophage.” He rus in a nonneuronal cell was demonstrated. These defined the plaque assay for quantitating bacteriophage, a advances all permitted the development of a plaque assay techniquetoenumeratevirusparticlesbasedontheirability for poliovirus 35 years after the concept was defined for to kill cultured cells and therefore produce holes, or bacteriophage. Basic studies on animal viruses that were plaques in the cell layer that became a keystone for defin- hindered by the necessity to work in animal systems were ingthepropertiesofviruses. now possible in vitro, and the principles established for The initial studies on tobacco mosaic virus led to fur- bacteriophage could be explored for animal viruses. The ther understanding of“filterable agents”—namely viruses. cellcultureeraofanimal virologyhadbegun. Specifically, the high concentration of virus produced in The advances in virology driven by human disease infected tobacco plants permitted the chemical and physi- control efforts were directly applicable to animal virol- cal characterization of the infectious material. By the ogy. Bovine viral diarrhea virus was identified as a new early 1930s, there was evidence that the agent infecting disease-causing agent in cattle in 1946 and by the late tobacco plants was composed of protein, and that antibo- 1950s was considered the most economically important dies produced in rabbits could neutralize the virus. The disease of cattle in the United States. Cell culture proce- tobacco mosaic virus was crystallized in 1935, and in dures permitted isolation of the virus and the production 1939 was the first virus to be viewed using an electron of a vaccine by the early 1960s. Influenza virus was microscope. The particulate nature of viruses was now an detectedfor the first time inwild birdsin1961, which led established fact. A further advance in animal virology to the identification of water fowl and shore birds as the was the use of embryonated eggs for culturing virus in natural reservoir of influenza A viruses. An apparent 1931. In the same year, Shope identified influenza virus cross-species incursion of a feline parvovirus variant pro- in swine; in 1933, influenza virus was isolated from duced theworldwideepizootic ofcanine parvovirusinthe human cases. The identification of the strain H1N1 of late 1970s. Again, standard in vitro cell culture proce- influenza virus in swine might be considered the first dures identified the new agent and soon enabled the pro- comprehensive description of an “emerging” disease in duction of an effective vaccine. The entire arterivirus animals—that is, a virus crossing a species barrier and family (Arteriviridae) was identified in the cell culture maintaining itself as an agent of disease in the new spe- era of virology—specifically, equine arteritis virus cies. In an attempt to move away from large-animal (1953),lactatedehydrogenase-elevatingvirus(1960),sim- experimentation, andtoprovidemodelsystemsforhuman ian hemorrhagic fever virus (1964), porcine reproductive diseases such as influenza, mice and rats became impor- and respiratory syndrome virus (1991), and most recently, tant tools for studying animal viruses. These advances wobbly possum virus (2012). The discovery of human spawned the birth of laboratory animal medicine pro- immunodeficiency virus (HIV) in 1983 attracted global gramsthathavebecomeanessentialbackboneofbiomed- attention, but the identification of simian immunodefi- icalresearch. ciency virus (SIV) shortly thereafter may ultimately be of The decade 1938(cid:1)48 saw major advances by Ellis, equal importance to the eventual control of human HIV Delbruck, and Luria in the use of bacteriophage to probe infection. The primate system has provided the animal the mechanism ofinheritance of phenotypic traits of these models for studies of pathogenesis and vaccine develop- bacterial viruses. Advances in understanding the proper- ment. Genetic analyses established that HIV-1 and HIV-2 ties of viruses progressed much more rapidly with bacte- were closely relatedtothe SIVspresent inOld World pri- rial viruses, because the work could be done in artificial mates, and that they were independently derived via media, without any requirement for laborious and time- cross-speciestransmissionofthesesimianviruses. consuming propagation of viruses in either animals or The beginnings of the molecular era of virology date plants. A key concept in virus replication, namely the to the late 1970s and early 1980s. Although not specifi- latent period, was defined using one-step growth curve cally designed for viruses, the development of the poly- experiments with bacteriophage (see Chapter 2: Virus merase chain reaction (PCR) in 1983 had a profound Replication). This observation of the loss of infectivity impact on virus research. Cloning of nucleic acid for a period after the initiation of the infection directed sequences led to the first infectious molecular clone of a research to define the mode of replication of viruses as virus (poliovirus) in 1981. The impact of molecular tech- totallydistinctfromthatofallotherreplicatingentities. niques on virus detection and diagnostics was demon- Animal virus studies made a dramatic shift in empha- strated with the identification of hepatitis C virus by sis with the development of reliable in vitro animal cell molecular means without isolation and in vitro propaga- cultures (1948(cid:1)55). As a result of intensive efforts to tion of the virus in cell culture. Viruses that could not be control poliovirus infections, single cell culture proce- easily cultured in vitro—such as papillomaviruses, noro- dures were defined, cell culture media were standardized, viruses, rotaviruses, and certain nidoviruses amongst

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Fenner's Veterinary Virology, Fifth Edition, is a comprehensive reference of global importance that features coverage on viral agents, viral diseases of animals, and newly emerging viral zoonotic diseases. It is an excellent first port of call for researchers and students alike, presenting the funda
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