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Viruses

Viruses. Egyptian stele (1580-1350 B.C) Crippled priest. Poxviruses (Poxviridae). The Pharaoh Ramses V died of smallpox (variola virus) in 1157 B.C. In 1520: 22 - 3.5 million Aztecs died Last case in Somalia on 26th October 1977 Sept.11—variola virus as a bioterrorism weapon?

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Viruses

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  1. Viruses

  2. Egyptian stele (1580-1350 B.C) Crippled priest

  3. Poxviruses(Poxviridae) • The Pharaoh Ramses V died of smallpox (variola virus) in 1157 B.C. • In 1520: 22 - 3.5 million Aztecs died • Last case in Somalia on 26th October 1977 • Sept.11—variola virus as a bioterrorism weapon? • Don’t confuse with chickenpox (varicella)

  4. VIRUSES • Virus = Latin for poison • Isolation of the first Virus • Dmitri Iwanowski in 1892 • Tobacco mosaic virus which affects >150 plants world wide stunted growth • “filterable agent”

  5. VIRUSES, LIVING ORGANISMS? • Life=A complex set of processes resulting from the actions of proteins specified by nucleic acids • Viruses: • Inert outside host cells • Obligate intracellular parasites • Do not divide

  6. VIRION • A complete, fully developed viral particle • Virions are the transmissible state of a virus. Metabolically inert • Virions must be able to adhere and allow entry into some host cell(s) • Also to survive outside of host cell environment. • Some virions more hardy than others (hepatitis virus A can withstand short periods of boiling; most virions are destroyed by this)

  7. VIRUS SIZE • Most, 20 to 300 nm • (0.02 to 0.3 mm) • Filoviruses up to 14,000 nm • Exceptional

  8. STRUCTURE OF VIRUSES • Only one type of nucleic acid (NA) • DNA or RNA • NA enclosed by a protein coat

  9. Circular Linear Types of viral nucleic acids Segmented

  10. VIRAL CAPSOMERS • Protein subunits, building blocks of the viral capsid

  11. STRUCTURE OF VIRUSES • Capsid composed of repeating subunits - capsomers • helical, icosahedral, complex • protection, attachment,

  12. ENVELOPED VIRUSES • Envelope present • Part of host’s cell membrane

  13. Structure of Viruses • Envelope derived from host membrane lipids and virus proteins • nuclear, plasma membrane by budding • necessary for attachment

  14. Nucleic acid Capsid Envelope

  15. NONENVELOPED OR NAKED VIRUSES • Envelope absent • More resistant than enveloped viruses

  16. "Naked" viruses require host death so viruses can be released • Enveloped viruses: are shed virus particles ; they shed by budding out, continued release from cell membrane • Cell does not die (immediately), continues to serve as factory for virus assembly and release. Virus typically acquires a coating of host cell membrane, and will include virus-specific proteins. This is the "envelope"

  17. Examples of enveloped viruses include: • Retrovirus, I.e. HIV • Paramyxovirus, I.e. influenza • Rhabdovirus, I.e. rabies • Enveloped Herpes virus

  18. Naked virus (no envelope) Nucleic acid Capsid

  19. TYPES OF VIRUSES • Animal viruses • Plant viruses • Bacteriophages (Virus that infects Bacteria) • Ex: Coliphage infect E.coli cells

  20. Types of Viral Infections Oncogenic viruses Herpes viruses

  21. VIRAL METABOLISM • Multiply using the machinery of the host cell • Have few or no enzymes

  22. HOST RANGE • Species specific • Small pox virus, humans • Broad host range • Rabies virus, mammals

  23. VIRAL SPIKES • Carbohydrate/protein complexes embedded in the viral envelope • Used as means of identification • Influenza virus, avian flue (H5N1)/Adenovirus

  24. Adenovirus spikes Respiratory Illness, Common Cold, “Pink Eye”, Gastrointestinal Illness

  25. VIRAL MORPHOLOGY • Helical • Cylindrical capsid with a helical structure • Polyhedral • Icosahedral (20 triangular faces and 12 corners)

  26. Helical nucleocapsid

  27. RHABDOVIRUS

  28. POLYHEDRAL

  29. VIRAL MORPHOLOGY (cont.) • Complex viruses • Structures attached to capsid • Tail, tail fibers • Bacteriophages

  30. Tail Bacteriophage

  31. POXVIRUS Infections due to the poxviruses (members of the Poxviridae family) occur in humans and animals. The orthopoxviruses include smallpox (variola), monkeypox, vaccinia, and cowpox viruses.

  32. CLASSIFICATION OF ANIMAL VIRUSES • Type of nucleic acid • DNA or RNA • Single stranded (ss) or double stranded (ds) • Presence of envelope

  33. CLASSIFICATION OF ANIMAL VIRUSES • Strategy for Replication • Where do they replicate? • Morphology • Structures • Described by common Names • Where is their niche? (Enteroviruses)

  34. Classification of viruses

  35. CLASSIFICATION OF ANIMAL VIRUSES (cont.) • ssDNA, nonenveloped • Parvovirus (Parvovirus B19 Fetal Death, GI) • dsDNA, nonenveloped • Adenovirus (Respiratory, GI) • Papovavirus (Warts, Tumors)

  36. CLASSIFICATION OF ANIMAL VIRUSES (cont.) • dsDNA, enveloped • Poxvirus (Smallpox, Cowpox) • Herpesvirus (Fever blisters, Chicken pox, Shingles, Mononucleosis) • Hepadnavirus (Hepatitis B, Tumors)

  37. HERPESVIRUS

  38. CLASSIFICATION OF ANIMAL VIRUSES (cont.) • ssRNA, nonenveloped • Picornavirus (Polio, Common Cold, GI) • dsRNA nonenveloped • Reovirus (GI, Respiratory) • dsRNA enveloped • Retrovirus (Tumors, AIDS)

  39. POLIOVIRUS

  40. Polivirus structure

  41. REOVIRUS Reoviruses are infectious agents of the virus family Reoviridae, transmitted by respiratory and fecal-oral routes. They are not major human pathogens reo (for respiratory, enteric, and orphan, the latter meaning not associated with human disease)

  42. RETROVIRUS They are enveloped viruses, with an RNA genome. The name is derived from the fact that the virus particle contains an RNA-dependent DNA Polymerase (Reverse transcriptase) This enzyme converts the RNA genome into DNA, which then integrates into the host chromosomal DNA. The reverse transcriptase is highly error prone and rapid genetic variation is a feature of this group

  43. CLASSIFICATION OF ANIMAL VIRUSES (cont.) • ssRNA, enveloped • Togavirus (Encephalitis) • Flavivirus (Dengue Fever, Yellow Fever, West Nile Virus) • Coronavirus (Common Cold) • Rhabdovirus (Rabies)

  44. CORONAVIRUS

  45. CLASSIFICATION OF ANIMAL VIRUSES (cont.) • ssRNA, enveloped • Filovirus(Ebola, Marburg) • Arenavirus(Hemorrhagic Fever) • Paramyxovirus(Mumps) • Orthomyxovirus (Influenza) • Bunyavirus (Hantavirus)

  46. FILOVIRUS Marburg and Ebola virus Appear in many different shapes (pleomorphic) First ID in Germany/Yugoslavia from tissues of green monkeys who developed hemorrhagic fever Filo = threadlike Filovirus. Although very "hot" in the news, these viruses are very poorly characterized because of their extreme pathogenicity. They are class IV pathogens, meaning they can only be cultured in total containment facilities, of which there are only two in the U. S. They are thought to be enveloped viruses with - RNA genomes.

  47. PART II

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