Microbiology Chapter #13

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Microbiology Chapter #13
2011-11-02 13:55:53
itsaji PHCC

Viruses, Viroids, and Prions
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  1. General Characteristics of Viruses
    • Obligatory intracellular parasites
    • Contain DNA or RNA
    • Contain a protein coat
    • Some are enclosed by an envelope
    • Some viruses have spikes
    • Most viruses infect only specific types of cells in one host
    • Host range is determined by specific host attachment sites and cellular factors
  2. Virus vs. Bacteria
    • No plasma membrane
    • Do not reproduce by binary fission
    • Don’t possess DNA and RNA simultaneously
    • No ribosomes
    • Don’t make ATP
    • Are not sensitive to antibiotics
    • Contain few or no enzymes of their own
  3. The spectrum of host cells a virus can infect is called it’s
    Host range (Host range is specific )
  4. Most viruses are only able to infect
    Specific types of cells in specific hosts
  5. Viruses that infect only bacteria are called
    Bacteriophages (phages)
  6. A completely developed viral particle is called a
  7. Nucleic acid of virus
    DNA or RNA
  8. Viral Structure:
    • Enveloped
    • Helical
    • Polyhedral
    • Long rods
    • Nucleic acid in a hollow cylindrical capsid
    • Rabies virus
    • Ebola virus
  10. VIRAL STRUCTURE: Polyhedral
    • Many-sided viruses
    • Many plant and animal viruses of this type
    • Icosahedron
    • Adenovirus
    • Polio virus
  11. Complex Viruses
    Bacterial viruses - Contain complex structures for transfer of DNA to host cell
  12. Taxonomy of Viruses, Viruses is grouped into families based on:
    • Nucleic acid type
    • Strategy for replication
    • Morphology
    • The suffix “-ales” is used for orders
    • The suffix “-viradae” is used for families
    • The suffix “-virus” is used as a genus name
    • Common names are used for species.
    • Subspecies are designated by a number.
  13. A ___ is a group of viruses sharing the same genetic information and ecological niche.
    Viral species
  14. Taxonomy of Viruses
    • Herpesviridae
    • Herpesvirus
    • Human herpes virus HHV-1, HHV-2, HHV-3
    • Retroviridae
    • Lentivirus
    • Human immunodeficiency virus HIV-1, HIV-2
  15. Growing Viruses
    Viruses must be grown in living cells
  16. ___form plaques on a lawn of bacteria
  17. Growing Animal Viruses
    Animal viruses may be grown in living animals or in embryonated eggs
  18. Growing Animal and plant Viruses
    Animal and plant viruses may be grown in cell culture. Continuous cell lines may be maintained indefinitely
  19. Virus Identification
    • Cytopathic effects
    • Serological tests
    • Nucleic acids ( Rflps, PCR)
  20. ___ Detect antibodies against viruses in a patient & Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot
    Serological tests
  21. Multiplication of Bacteriophages (Lytic Cycle)
    • Attachment: Phage attaches by tail fibers to host cell
    • Penetration: Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell
    • Biosynthesis: Production of phage DNA and proteins
    • Maturation: Assembly of phage particles
    • Release: Phage lysozyme breaks cell wall
  22. Multiplication of Animal Viruses
    • Attachment: Viruses attach to cell membrane
    • Penetration: by endocytosis or fusion
    • Uncoating: by viral or host enzymes
    • Biosynthesis: Production of nucleic acid and proteins
    • Maturation: Nucleic acid and capsid proteins assemble
    • Release: by budding (enveloped viruses) or rupture
  23. Biosynthesis of DNA Viruses
    • DNA replicated in the nucleus and the capsid is replicated in the cytoplasm.
    • Capsid proteins then migrate to the nucleus.
    • Virons are formed in the nucleus.
    • Virons transported along Endoplasmic reticulum to the plasma membrane for release.
  24. DNA Containing Viruses
    • Parvovirdae
    • Adenovirdae
    • Poxvirdae
    • Herpesviridae
    • Papovavirdae
    • Hepadnavirdae
  25. Parvoviridae
    • Single-stranded DNA, nonenveloped viruses,
    • Fifth disease
    • Anemia in immunocompromised patients
  26. Adenoviridae
    • Double-stranded DNA, nonenveloped viruses
    • Respiratory infections in humans
    • Tumors in animals
  27. Poxviridae
    • Double-stranded DNA, enveloped viruses
    • Orthopoxvirus (vaccinia and smallpox viruses)
    • Molluscipoxvirus
    • Smallpox
    • Molluscum contagiosum
    • Cowpox
  28. Herpesviridae
    • Double-stranded DNA, enveloped viruses
    • Simplexvirus (HHV-1 and HHV-2)
    • Varicellovirus (HHV-3)
    • Lymphocryptovirus (HHV-4)
    • Cytomegalovirus (HHV-5)
    • Roseolovirus (HHV-6)
    • HHV-7
    • Kaposi's sarcoma (HHV-8)
    • Some herpesviruses can remain latent in host cells
  29. Papovaviridae
    Double-stranded DNA, nonenveloped viruses
  30. Papillomavirus
    Human wart virus
  31. Polyomavirus
    Cause tumors; some cause cancer
  32. Hepadnaviridae
    • Double-stranded DNA, enveloped viruses
    • Hepatitis B virus
    • Use reverse transcriptase
  33. RNA Containing Viruses
    • Picornavirdae
    • Togaviridae
    • Rhabodoviridae
    • Caliciviridae
    • Reoviridae
    • Retroviridae
  34. Picornaviridae
    • Single-stranded RNA, + strand, nonenveloped
    • Enterovirus: Poliovirus and coxsackievirus
    • Rhinovirus
    • Hepatitis A virus
  35. Togaviridae
    • Single-stranded RNA, + strand, enveloped
    • Alphavirus :Transmitted by arthropods; includes EEE and WEE
    • Rubivirus (rubella virus)
  36. Rhabdoviridae
    • Single-stranded RNA, – strand, one RNA strand
    • Vesiculovirus
    • Lyssavirus (rabies virus)
    • Cause numerous animal diseases
  37. Caliciviridae
    • Single-stranded RNA, + strand, nonenveloped
    • Hepatitis E virus
    • Norovirus causes gastroenteritis
  38. Reoviridae
    • Double-stranded RNA, nonenveloped
    • Reovirus (respiratory enteric orphan)
    • Rotavirus (mild respiratory infections and gastroenteritis)
    • Colorado tick fever
  39. Retroviridae
    • Single-stranded RNA, 2 RNA strands,
    • produce DNA
    • Use reverse transcriptase to produce DNA from viral genome
    • Lentivirus (HIV)
    • Oncogenic viruses
    • Includes all RNA tumor viruses
  40. Cancer
    • Several cancers are known to be caused by viruses
    • Often go un-noticed
    • Most viruses do not cause cancer
    • Cancer takes a long time to develop
    • Cancer is not contagious like viruses
    • Viruses cause cancers by activating oncogenes
    • Only 10% of cancers have been liked to viruses
  41. ___transform normal cells into cancerous cells
    • Transformed cells have increased growth, loss of contact inhibition, tumor-specific transplant antigens, and T antigens
    • Activated oncogenes
  42. Many virus can remain in the infected host for long periods of time without causing a disease- Latent viral infections Several examples: Herpes simplex-1 virus (fever blisters), Chickenpox and Shingles
    Latent Viral Infection
  43. Persistent Viral Infection
    • Prolonged viral infections, usually fatal, Different from a latent infection in that the infectious virus grows in numbers over time until it is detected. Some persistent viral infections can be caused by conventional viruses.
    • Subacute sclerosing panencephalitis (measles virus)
  44. Prions
    Proteinaceous Infectious particle, Inherited and transmissible by ingestion, transplant, and surgical instruments, Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease, Kuru
  45. Plant Viruses
    • Plant viruses are similar to animal viruses in most respects
    • Plant viruses can cause many diseases
    • Bean mosaic virus (Beans)
    • Wound tumor virus (Corn)
    • Potato yellow dwarf virus (potatoes)
    • Usually infect plants through damage to cell wall (worms, fungi, insects) and is transferred from plant to plant through pollen.
  46. Viroids
    • Viroids are short pieces of naked RNA with not protein coat
    • Nucleotides are often paired, folded, and three-dimentional
    • Nucleotide does not code for proteins
    • Only a plant pathogen of potatoes