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RNA VIRUSES

RNA VIRUSES. All are ss (single stranded) except Reoviridae All replicate in the cytoplasm except Orthomyxoviruses (in some process). Single-stranded RNA (linear), + strand, nonenveloped “pico” – small, Icosahedral. Involving humans. Enterovirus

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RNA VIRUSES

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  1. RNA VIRUSES • All are ss(single stranded) except Reoviridae • All replicate in the cytoplasm except Orthomyxoviruses (in some process)

  2. Single-stranded RNA (linear), + strand, nonenveloped“pico” – small, Icosahedral • Involving humans • Enterovirus • Polioviruses, Coxsackieviruses A, B and Echovirus (acid- stable) • Rhinovirus (common cold, acid-laible) • Hepatovirus, Hepatitis A virus • Involving animals • Foot-and-mouth disease of cattle • Encephalomyocarditis of rodents poliomyelitis

  3. Single-stranded RNA (linear), + strand, nonenvelopedcup- like surface, Icosahedral • Norovirus (Norwalk agent) causes acute epidemic gastroenteritis • Similar to picornaviruses but slightly larger

  4. Astroiviridae Single-stranded RNA (linear), + strand, nonenvelopedstar- like surface, Icosahedral • causes gastroenteritis in humans and animals • Similar in size to picornaviruses

  5. Hepeviridae Genome : ssRNA (Linear), + strand, nonenveloped, Icosahedral • Human Hepatitis E virus cause acute hepatitis

  6. Double-stranded RNA (linear), + strand, nonenveloped, two or three shell, Icosahedral, segmented (10-12)Rota: wheel-shape appearance, Respiratory Enteric Orphan (REO) • Rotavirus: acute gastroenteritis, • Coltivirus: arbovirus (Colorado tick fever) • Genome segment reassortment occurs readily

  7. An ecologic grouping (not a virus family) of viruses with diverse • physical and chemical properties. • Arboviruses infect humans, mammals, birds, and snakes • Arboviruses are transmitted by arthropods; • Arthropods: Mosquitoes, ticks, flies • Arboviruses: Toga, Flavi, Bunya, Rabdo, Arena and Reo viruses • Human pathogens include dengue, yellow fever, • encephalitis viruses, and others.

  8. Single-stranded RNA (linear), + strand, enveloped, Icosahedral • Alphavirus (arbovirus) • Include EEE, WEE, VEE (Eastern, western and venezuelan equine encephalitis viruses) • Rubivirus (rubella virus)

  9. Single-stranded RNA (linear), + strand, enveloped, unknown symmetry • Flaviviruses (Arboviruses): Yellow fever, dengue, St. Louis Encephalitis and West Nile viruses • Hepaciviruses: Hepatitis C virus

  10. Coronaviridae • Petal-shaped surface, like a solar corona • More human coronaviruses cause upper respiratory infections • Severe acute respiratory syndrome (SARS)

  11. Single-stranded RNA (linear), – strand, helical symmetry, bullet shape, enveloped • Lyssavirus (rabies virus) • Cause numerous animal diseases

  12. Bornaviridae • Single-stranded RNA (linear), – strand, helical symmetry, enveloped • Borna disease virus (BDV) • neurotropic in animals and belongs a severe (frequently fatal) neurological disease of horses and sheep

  13. Single-stranded RNA (linear), – strand, enveloped,Helical symmethery, large peplomer • Ebola and Marburg viruses, causing hemorrhagic fever in Africa • Require maximum containment conditions (Biosafety Level 4) for handling

  14. Single-stranded RNA (linear), - strand, segmented (6-8),shift and drift antigenic, Helical symmetry , enveloped, • The segmented nature of the viral genome permits ready genetic reassortment • Influenza virus (Influenza A, B and C viruses) • Haemagglutinin (HA) and neuraminidase (NA)

  15. Paramyxoviridae Genome : ss RNA ,(-) RNA , linear Virion : Helical symmetry , pleomorphic , enveloped Genetically stable • Paramyxoviruses (parainfluenza, mumps virus: H+, N+) • Morbillivirus (measles virus, H+, N-) • Pnuemonovirus (respiratory syncytia virus, metapneumovirus, H-, N-)

  16. Single stranded RNA (circular), – strand or ambisense, segmented (3) Helical symmetry, enveloped • budding from Golgi • Most are arboviruse: Sand fly fever ,California encephalitis virus, La crosse , Crimian-congo fever viruses are Arbovirus and cause hemorrhagic fever • Hantaviruses are transmitted by infected rodents via aerosols. (They cause hemorrhagic fevers and nephropathy as well as a severe pulmonary syndrome)

  17. Single-stranded RNA (circular),– strand or ambisense, segmented (2), sandy shape, Helical symmetry • The virions incorporate host cell ribosomes during maturations, which gives the particles a "sandy" appearance (sandy) • Lassa Fever (Africa), Tacaribe virus complex (junin and machupo viruses, America) cause hemorrhagic fever in human • Cause chronic infections in rodents

  18. Single-stranded RNA (linear), + strand, icosahedralenveloped, two copy of genome • Includes all RNA tumor viruses • Use reverse transcriptase to produce DNA from viral genome • Lentivirus (HIV, Visna of sheep) • Leukemia and sarcoma viruses of animals and humans (HTLV-1) • Foamy viruses of primates

  19. General steps in viral replication cycles 1- Attachment, penetration and uncoating 2- Expression of viral genome and synthesis of viral components 3- Morphogenesis and release

  20. virus entry Uncoating genome replication Protein synthesis virus-assembly and maturation Virus release Viral replication – basic principles Host cell Protein synthesis is directed exclusively by the cellular machinery

  21. Attachment • The first step in infection of a cell is attachment to the cell surface, interaction of a virion which a specific receptor site on the surface on the cell. • Receptor molecules differ for different viruses but are generally glycoproteins. - In some cases : • virus binds protein sequences (eg, picornaviruses) • in others oligosaccharides (eg, orthomyxoviruses and paramyxoviruses ) Viral glycoproteins Cell receptor

  22. Penetration • After binding, particle taken up inside the cell. • Enveloped viruses • (A) Entry by fusing with the plasma membrane. Some enveloped viruses fuse directly with the plasma membrane. Thus, the internal components of the virion are immediately delivered to the cytoplasm of the cell • (B) Entry via endosomes at the cell surface . Some enveloped viruses require an acid pH for fusion to occur and are unable to fuse directly with the plasma membrane. • Non-enveloped virusesNon-enveloped viruses may cross the plasma membrane directly or may be taken up into endosomes. They then cross (or destroy) the endosomal membrane

  23. Uncoating genome replication Protein synthesis Uncoating, Expression of viral genome and synthesis of viral components • Uncoating is the physical separation of the viral nucleic acid from capsid • The infectivity of the parental virus is lost at the uncoating stage • Specific mRNAs must be transcribed from the viral nucleic acid for successful expression and duplication of genetic information. • Then, virus use cell components to translate the mRNA. Host cell

  24. virus-assembly and maturation Virus release Morphogenesis and release • Newly synthesized viral genomes and capsid polypeptides assemble together to form progeny viruses. • Virus may be released due to cell lysis, or, if enveloped, may bud from the cell. Budding viruses and do not necessarily kill the cell. • - Thus, some budding viruses may be able to set up persistent infections. - Icosahedral capsids can condense in the absence of nucleic acid • - Nucleocapsids of viruses with helical symmetry cannot form without viral RNA

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