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Infectious Disease > Week 2: Virology > Flashcards

Week 2: Virology Flashcards

1
Q

What is a virus?

A

Intracellular obligate parasite

  • unable to replicate outside of a host cell
  • Unable to make own proteins
  • Depends on the cell machinery for replication and protein production
  • Are NOT living
  • must be able to infect a host to survive
  • Viral components are assembled - do not replicate by division
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2
Q

How do viruses enter cells?

A

Via host cell receptors

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3
Q

Viral genes expressed how?

A

using viral and/or host-encoded functions

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4
Q

What do viral proteins do?

A
  • modify host cell functions to ensure viral replication
  • Assemble into caspids that protect viral genomes
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5
Q

How do viruses propagate?

A

Viral proteins modify host cell functions to ensure viral replication and assemble into capsids that protect viral genomes and then the virus is released to infect new cells.

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6
Q

Range of viral infections?

A

Demonstrates viral tropism (viruses are found infected certain parts of the body because those tissues have receptors to allow viral entry)

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7
Q

Describe viral entry into the skin

A

require a breach of the physical integrity of the skin barrier and employs vectors

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8
Q

Describe viral entry into the conjunctiva and other mucous membranes

A

rather exposed site and relatively unprotected

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9
Q

Describe viral entry into the respiratory tract

A

possess sophisticated immune defense mechanisms which viruses must overcome

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10
Q

Describe viral entry into the Gastrointestinal Tract

A

gastric acid, bile salts, etc. provide a difficult environment so viruses would need to be adapted to infect and spread in this hostile environment

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11
Q

Describe viral entry into the genitourinary tract

A

relatively less hostile than the GI tract but is less frequently exposed to extraneous viruses

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12
Q

Factors affecting viral tissue tropism

A
  • Correct attachment protein to bind to a receptor on the cell surface to gain entry
  • Appropriate cellular machinery present within the host cell to allow the virus to replicate
    • Are dividing cells with high enough levels of dNTPs for viral DNA synthesis
  • A way to exit the host cell to spread the infection
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13
Q

Describe the steps of a typical viral infection

A
  • Primary replication
  • Systemic spread
  • Secondary replication
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14
Q

Describe the primary replication step of a viral infection

A
  • the place of primary replication where the virus replicated after gaining initial entry into the host cell
  • This frequently determines whether the infection will be localized at the site of entry or spread to become a systemic infection
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15
Q

Describe the systemic spread step of a viral infection

A

Apart from direct cell-to-cell contact, the virus may spread via the bloodstream and the CNS

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16
Q

Describe the Secondary Replication step of a viral infection

A

Secondary replication takes place at susceptible tissues/organs following systemic spread

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17
Q

Describe acute viral infection outcomes

A
  • Recovery with no residue effects (respiratory viruses)
  • Recovery wit residue effects (eg. acute viral encephalitis leading to neurological sequelae)
  • Death (Ebola virus)
  • Proceed to chronic infection
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18
Q

Describe chronic viral infection outcomes

A
  • Silent subclinical infection for life e.g. CMV, EBV
  • A long-silent period before disease e.g. HIV, SSPE, PML
  • Reactivation to cause acute disease e.g. herpes and shingles
  • Chronic disease with relapses and excerbations e.g. HBV, HCV
  • Cancers e.g. EBV, HTLV-1, HPV, HBV, HCV, HHV-8
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19
Q

Describe the possible viral pathogenesis time lines

A
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20
Q

Describe the virus-host interaction

A
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21
Q

Describe the ways the cells can respond to viral infections

A

cells can respond to viral infections in 3 ways

  • Failed infection (abortive infection)
    • non-permissive cell
  • Cell death (lytic infection)
    • prevent cellular growth
    • disrupt the structure and function of cells
  • Replication without cell death (persistent infection)
    • chronic - nonlytic viral synthesis
    • Latent - limited viral synthesis
    • Recurrent - periodic productivity
    • Transforming - immortalization of cell
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22
Q

What are prions?

A

Infectious proteins that causes a very slow infection happening a very long-time before the disease episode

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23
Q

Describe cellular pathogenesis of a persistent viral infection

A
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24
Q

How are cells damaged by a viral infection?

A
  • Direct cell damage and possibly death from a viral infection
  • Indirect cell damage as a result of a viral infection
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25
Q

Describe direct cell damage and possibly death from a viral infection

A
  • Diversion of a cell’s energy
  • Shutoff of a cells macromolecular synthesis
  • Competition of viral promoters and transcriptional enhancers for cellular transcriptional factors such as RNA polymerases and inhibition of the interferon defense mechanisms
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26
Q

Describe indirect cell damage as a result of a viral infection

A
  • integration of the viral genome
  • induction of mutations in the host genome
  • inflammation
  • host-immune response
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27
Q

Describe the viral life cycle

A
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28
Q

How are viruses classified?

A
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29
Q

Describe the difference between RNA and DNA viruses

A
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30
Q

What is viral symmetry?

A

Symmetry refers to the way in which capsomere units are arranged in viral capsid. Two kinds of symmetry are recognized in the viruses which corresponds to two primary shape ie. Rod and spherical shape of virus. Rod shaped virus have helical symmetry and spherical shaped virus have icosahedral symmetry

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31
Q

What types of viral symmetry are there?

A

5 types

  • Naked icosahedral
  • Naked helical
  • Enveloped icosahedral
  • Enveloped helical
  • Complex
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32
Q

Examples of Naked Icosahedral viruses

A
  • Poliovirus
  • Adenovirus
  • Hepatitis A virus
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33
Q

Examples of Naked helical viruses

A

No known human viruses

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34
Q

Examples of Enveloped Icosahedral viruses

A
  • herpes virus
  • yellow fever virus
  • Rubella virus
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35
Q

Examples of Enveloped Helical viruses

A
  • Rabies virus
  • Influenza virus
  • Parainfluenza virus
  • Mumps virus
  • Measles virus
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36
Q

Examples of complex viruses

A

e.g. Poxvirus

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37
Q

Naked icosahedral viruses

A

Poliovirus

Adenovirus

Hepatitis A virus

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38
Q

Naked helical viruses

A

No known human viruses

39
Q

Enveloped icosahedral viruses

A

Herpes virus

Rubella virus

Yellow fever viruses

40
Q

Enveloped helical viruses

A

Rabies virus

Influenza virus

Parainfluenza virus

Mumps virus

Measles virus

41
Q

Complex viruses

A

poxvirus

42
Q

Capsid virus assembly

A

Individual proteins -> larger units

43
Q

Capsid viruses environmental stability

A

Environmentally stable

44
Q

Enveloped viruses environmental stability

A

Environmentally liable

45
Q

DS DNA viruses

A

Polyoma

Papilloma

Adeno

Herpes

Pox

46
Q

SS DNA viruses

A

Parvo

47
Q

+RNA viruses

A

Picorna

Noro

Toga

Flavi

Corona

48
Q

-RNA viruses

A

Rhabdo

Paramyxo

Orthomyxo

Bunya

Filo

49
Q

DSRNA viruses

A

Reovirus

50
Q

Retroviruses

A

Retrovirus

51
Q

DNA virus replication

A

Viral DNA resembles host DNA

Replication requires a DNA-dependent DNA polymerase

52
Q

DNA virus early genes

A

Encode DNA-binding proteins

53
Q

DNA virus Late genes

A

Encode structural proteins for assembly

54
Q

DNA virus transcription location

A

Transcription occurs in the nucleus

*Except for Poxviruses* which encode their own polymerase and transcription occurs in the cytoplasm

55
Q

DS DNA viruses

A

Herpesviruses

Adenoviruses

Papovaviruses

Poxviruses (Complex DNA virus)

56
Q

SS DNA viruses

A

Parvovirus

57
Q

Describe replication of simple DNA virus

A

DNA virus uses host cell machinery to replicate

DNA replication occurs in the nucleus

58
Q

Describe replication of Complex DNA virus: Poxvirus

A

Replication occurs in the cytoplasm

Provide their own mRNA and DNA synthetic machinery

59
Q

SS +RNA enveloped icosahedral viruses

A

Flaviviridae

Togaviridae

Retroviridae

60
Q

SS +RNA enveloped helical viruses

A

Coronaviridae

61
Q

SS +RNA nonenveloped icosahedral viruses

A

Picornaviridae

Calciviridae

62
Q

SS -RNA enveloped helical viruses

A

Orthomyxoviridae

Paramyxoviridae

Rhabdoviridae

Filoviridae

Bunyaviridae

Arenaviridae

63
Q

DS -RNA nonenveloped icosahedral viruses

A

Reoviridae

64
Q

RNA viruses characteristics

A
  • Must encode an RNA-dependent RNA-polymerase
  • Host cells have no mechanism of replicating RNA
  • RNA polymerases are error-prone
  • RNA is very liable and can be degraded by the cell
  • All RNA viruses must carry their own polymerase
  • *Except (+) RNA viruses
65
Q

Describe replication of simple RNA viruses

A
66
Q

DS RNA viruses mechanism of replication

A

Reoviruses

Birnaviruses

The virion RNA is DS and so cannot function as mRNA

Viruses package an RNA polymerase to make their mRNA after infection of the host cell

67
Q

SS + RNA viruses

A

Picornaviruses

Togaviruses

Coronaviruses

Flaviviruses

68
Q

SS +RNA viruses transcription

A

In these viruses the genomic RNA functions as mRNA

This mRNA can be translated immediately upon infection of the host cell using host cell machinery-> it is infectious

69
Q

SS -RNA viruses

A

Orthomyxoviruses

Rhabdoviruses

Paramyxovirus

Filovirus

Bunyavirus

70
Q

SS -RNA viruses transcription

A

The virion RNA is negative sense -> must be copied into the plus-sense mRNA before proteins can be made

Packaged in the virion so that they can make mRNAs upon infecting the cell

Transcription and replication occurs in the cytoplasm *Except for influenza virus*

71
Q

SS -RNA viruses transcription location

A

Transcription and replication occurs in the cytoplasm *Except for influenza virus*

72
Q

Retroviruses genome

A

Two identical (+)sense ssRNAs

Neither directly transcribed nor translated

Viral RNA-dependent DNA polymerase (reverse transcriptase) co-packaged with the viral genome

Converts ssRNA into ds DNA

Proviral cDNA integrated into the host genome

Proviral genes transcribed by cellular RNA polymerase II

Human pathogens: HIV-1, HIV-2, human T-cell leukemia virus (HTLV)-1 and HTLV-2

73
Q

Describe Influenza virus genetics in action

A
  • Surrounding the helical nucleocapsids is a lipid envelope with two viral glycoproteins: Hemagglutinin (H or HA) and neuraminidase (N or NA)
  • Genome consists of 8 individual segments of SS negative polarity RNA
  • Segments assemble at random into virions, some of which are infectious
  • Viral RNA polymerase is error-prone due to lack of proofreading activity so there is a high-mutation rate
74
Q

How are influenza virus strains identified?

A

Strains are identified by the specific H and N antigen combination (eg H3N1)

75
Q

Describe influenza virus RNA polymerase

A

polymerase is error-prone due to lack of proofreading activities, like most RNA viruses thus there is a high mutation rate

76
Q

Epidemiology of influenza viruses

A
  • May be endemic epidemic or pandemic
  • Epidemics result from antigenic changes in the SAME virus
  • Pandemics result from the emergence of a new influenza virus *Only occurs in influenza A*
77
Q

Describe Antigenic drift

A
78
Q

Effects of antigenic drift

A

Major changes in the viral antigens circulating the population

79
Q

What are zoonotic viruses

A
  • viruses that also infect animals
  • such as influenza A where birds and swine act as reservoirs
80
Q

What is the key factor regarding antigenic shifts in influenza A

A

Zoonotic aspect of Influenza A

81
Q

Factors regarding antigenic shifts in influenza A

A
  • Zoonotic
  • Individual cells may multiply infected with viruses of different strains in birds, swine or humans
  • Segmented nature of the influenza genome
  • The end result is that random recombination of RNA segments from different strains of virus (including from different species)
82
Q

Bacteria cell type

A

Prokaryotic

83
Q

Virus cell type?

A

non-classified

84
Q

Bacteria size of cell

A

typically 0.2-2.0 μm

85
Q

Viruses size of cell

A

18-300 nm

86
Q

Bacteria nucleic acid

A

Single circular chromosome (DNA)

87
Q

Bacteria metabolism

A
  • Heterophilic
  • Aerobic
  • Anaerobic
88
Q

Bacteria reproduction

A

Most capable of independent reproduction

89
Q

Bacteria method of cultivation

A

Visible growth on agar surface for most

90
Q

Virus nucleic acid

A
  • RNA or DNA
  • Single or double-stranded
91
Q

Virus metabolism

A

Dependent on host machinery

92
Q

Virus reproduction

A

Dependent on host machinery

93
Q

Virus method of cultivation

A
  • No visible growth on agar
  • requires host cells for propagation

Infectious Disease (82 decks)

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