ENVR 421 Viruses: OverviewVirusesVirus CompositionSlide 4Virus Replication and InfectivityTaxonomyClassification based upon:Important Definitions For Virus ReplicationThe Central Dogma of Molecular BiologySlide 10Slide 11Replication of a Nonenveloped RNA VirusReplication of an Enveloped VirusViruses and the EnvironmentImportant Human Enteric Viruses (150+)EnterovirusesHepatitis A Virus (HAV)Slide 18Slide 19Slide 20Hepatitis E VirusSlide 22Reovirus and RotavirusesRotavirusesADENOVIRUSES:Noroviruses and Other CalicivirusesResponse of Human Volunteers to Norwalk Virus Infection via the Oral RouteImportant Human Respiratory VirusesInfluenza VirusesParamyxovirusesRhinovirusesCoronavirusesSARS - CoronavirusesSARS: Clinical DetectionSARSAssay Methods for VirusesVirus Infectivity and Infectivity AssaysVirus Detection in Cell Culture by Cytopathogenic EffectsQuantifying Human Virus Infectivity is a ChallengeProgress in Virus Detection in Cell CultureSlide 41Slide 42Virus Infections: Some Important Viruses Cause Localized Infections and Others Systemic InfectionsFactors Influencing Virus Infection and IllnessRole of Immunity in Virus Infections: Generalized/Systemic/Disseminated InfectionsRole of Immunity in Virus Infections: Localized Infections:Role of Selection of New Viral Strains in Susceptibility to Infection and IllnessENVR 421Viruses: OverviewMark SobseyViruses•Not cellular organisms•Small: –0.02-0.3 µM diameter•simple: –nucleic acid–protein coat–(lipoprotein envelope) •shape: –spherical (icosahedral)–rod-shaped (helical)–complexVirus Composition•nucleic acid:–RNA or DNA–double- or single-stranded–one piece or multiple, genetically distinct pieces •represent separate genes•some have multiple copies of same gene–linear, circular or circular+supercoiledVirus Composition•protein coat or capsid:–contains one or more distinct proteins; multiple copies of each –proteins arranged in a stable array to form capsid–some proteins on virus surface are glycosylated•envelope:–usually derived from cell membrane•lipid bilayer with inserted virus-specific proteins (peplomers)•acquired from cell upon exiting (“budding”)Virus Replication and Infectivity•no biological activity outside of host cells/or host organisms•obligate intracellular parasites; active only in host cell•recruit host cells biosynthetic machinery and building blocks to make new viruses •typically produce 1000s to 100,000s per infected cell•often destroy (lyse) the host cell as a result of infection–some viruses: host cell survives to shed viruses over time•productive infection–other viruses: host cell survives and is transformed by presence of virus genes •tumor virusesTaxonomy•Classify into groups based upon common physical/chemical properties•Viruses in same group often have similar biological properties–Replication–Disease–SpreadClassification based upon:•Genome (RNA, DNA, SS, DS etc)•Morphology of virion, envelope•Replication strategy•Serological relationships (Serotypes)International Committee onTaxonomy of VirusesImportant Definitions ForVirus Replication•Virion – a virus particle; the virus nucleic acid surrounded by a protein coat and sometimes, a lipoprotein envelope•Messenger RNA (mRNA) – an RNA molecule transcribed from DNA that contains the genetic material necessary to encode a particular protein•Plus-strand (+) nucleic acid – an RNA or DNA strand that has the same sense as the mRNA of a virus (can act as mRNA > make viral proteins)•Minus- strand (-) nucleic acid – an RNA or DNA strand that has the opposite sense (complementary) of the mRNA of a virusThe Central Dogma of Molecular BiologyDNAReplicationRNA (mRNA)ProteinTranscriptionTranslation Transcription is carried out by RNA polymeraseTranslation is carried out by ribosomes in the cellReplication is carried out by DNA polymeraseReverse transcriptase copies RNA to DNAVirus – “Life Cycle”1. Attachment / Adsorption2. Penetration1. translocation2. endocytosis3. fusion3. Uncoating4. Biosynthesis: Replication and Transcription•segmented: monocystronic mRNA•non-segmented: polycistronic mRNA5. Synthesis and assembly6. Release7. Maturation•virus becomes infectious•may be linked to release or may occur after the virus has been releasedReplication of a Nonenveloped RNA VirusReplication of an Enveloped VirusViruses and the Environment•non-enveloped viruses are most persistent in the environment than enveloped viruses– protein coat confers stability and resistance to stressors•enteric viruses are important for environmental health –transmitted by direct and indirect contact, fecally contaminated water, food, fomites and air.–Most enteric viruses are nonenveloped•respiratory viruses also important –transmitted by direct and indirect contact, air and fomites (some by water and food, too)–some respiratory viruses are nonenveloped (rhinoviruses and adenoviruses)–others are enveloped (influenza viruses and coronaviruses)Viruses/Groups Animals Reservoirs?Enteroviruses: no(polios, echos*, coxsackies*, etc.)Hepatitis A virus noHepatitis E virus pigs?; rats?Reoviruses yesRotaviruses yes**Adenoviruses*yes**Caliciviruses*: Norwalk, Snow Mountain, etc. Cattle? Swine?Astroviruses uncertain*On EPA’s candidate contaminants list (CCL)**Humans & animals infected by different ones; but not always.Important Human Enteric Viruses (150+)Enteroviruses•Icosahedral shape•~27-30 nm diameter•single-stranded +sense RNA–about 7,500 nucleotides•icosahedral protein coat (capsid)–4 capsid proteins: VP1, VP2, VP3, VP4 (all cleaved from VP0)•>71 antigenically distinct human types–polioviruses (3 types)–coxsackie B viruses (6 types)–coxsackie A viruses (23 types)–echoviruses (31 types)•distinct animal enterovirusesHepatitis A Virus (HAV)•icosahedral•27 nM in diameter•non-enveloped capsid•ss(+) RNA genome•At least 3 major structural polypeptides•Single serotype•Infects humans and non-human primates•Cell culture reported in 1979 in fetal rhesus monkey kidney cellsHepatitis A Virus (HAV)•Fecal-oral route of exposure•Incubation period: 2-6 weeks•Serious debilitating disease (general infection): fever, abdominal pain, headache, jaundice, nausea, diarrhea•Fecally excreted at concentrations up to 106 infectious units per gram (>109 virions per gram)•Infectious at relatively low doses•Persistent in feces, sewage, soil and