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HHAD: Microbiology > Intro to viruses > Flashcards

Intro to viruses Flashcards

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Biology 101 flashcards
1
Q

Name the 6 characteristics/factors a virus has

A
  • Natural history/life cycle
  • Mode and efficiency of transmission
  • Tropism (directional growth)
  • Invasiveness
  • Opportunism
  • Virulence
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2
Q

What 5 factors must a host have that may make them susceptible to viral infection?

A
  • Age
  • Genetic predisposition
  • Immune status
  • Specific immunity (active/passive)
  • Trauma/surgery/foreign body
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3
Q

Do viruses colonise skin, like bacteria?

A

No

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4
Q

Name 5 examples of sources of viruses

A
  • Social
  • Food/water
  • Environmental
  • Occupational
  • Nosocomial
  • Sexual
  • IVDU (intravenous drug users)
  • Travel
  • Animal
  • Arthropod-borne
  • Congenital
  • Perinatal (around process of birth)
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5
Q

What are the 3 ways in which exposure may occur - i.e. what routes could these viruses take to enter the body? (route of exposure)

A

Oral
Respiratory (inhalation)
Percutaneous (skin/mucous membrane)

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6
Q

Outline the structure of a virus (4)

A

Polymerase protein
Capsid core (protects DNA/RNA)
DNA or RNA genome (never both)
Envelope (non-essential component)- viruses may or may not have an envelope

(the other 3 components are essential)

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7
Q

What type of microorganism could viruses be classified as?

A

Obligate intracellular parasites

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8
Q

What do the viruses DNA or RNA often code for and why?

A

The code for structural and functional proteins needed for self-perpetuation

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9
Q

How are new virus particles formed?

A

They are formed by assembly of components synthesised using host cell proteins

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10
Q

What characteristics are used to classify viruses into families? (5)

A

Type of nucleic acid (DNA or RNA)
Symmetry of nucleocapsid
Lipid envelope (presence of absence)
Number of strands of nucleic acids (single or double) and their physical construction (e.g. segmented)
Polarity of viral genome (e.g. positive of negative strand RNA)

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11
Q

Capsids of RNA viruses may be one of which 2 shapes?

A

Icosahedral

Helical

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12
Q

Capsids of DNA viruses may be one of which 2 shapes?

A

Icosahedral

Complex (always enveloped)

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13
Q

What are capsids made from?

A

Capsomeres

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14
Q

What are capsomeres?

A

They are virally-encoded protein subunits that make up the capsid

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15
Q

Describe the icosahedral capsid of a virus

A

Capsid composed of 20 solid equilateral triangles arranged around face of a sphere
Simplest is made by 3 identical subunits to form each face, so minimum number of subunits in icosahedral capsid is 60 (20x3)
Structural units may be made of more than one viral protein

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16
Q

What is the minimum number of subunits an icosahedral capsid can be made from?

A

60 (20 x 3)

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17
Q

Describe the helical capsid of a virus

Which type of virus does this only occur (in humans)?

A

Capsomeres bound in periodic fashion to viral genome, so it winds the genome into a helix
Among human viruses, this symmetry only occurs in RNA viruses (e.g. ebola virus)

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18
Q

Describe the complex capsid of a virus

What is the only human virus to have this symmetry?

A

Capsid neither purely helical or icosahedral
Nucleocapsid is a continuous cylinder surrounded by a lipid layer and complex proteinaceous core wall (pallisade layer)

Poxviruses (e.g. smallpox)

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19
Q

Why are viral surface proteins important? (3)

A

Attach to membrane proteins (receptors) in host cell - determinants of tropism
Target for antibodies - neutralisation
Determinants of antibody specificity (serotype)

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20
Q

What is the viral envelope and what does it contain?

A

Lipid bilayer derived from host cell membrane
Contain viral glycoproteins (spikes) that project from the membrane

(envelope not present in all viruses)

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21
Q

Do non-enveloped viruses survive outside of the host cell? How may they be transmitted?

Name examples (2)

A

Naked viruses are stable in environment; may be transmitted by food or water

e.g. noroviruses, polio, hep A (picornaviruses)

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22
Q

Do enveloped viruses survive outside of the host cell? How may they be transmitted?

Name examples (2)

A

They only survive transiently outside host and don’t persist in environment. Spread by close or intimate contact.

e.g. influenza, HIV, Hep B

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23
Q

What are the basic steps of viral replication (7)

A

1a. attachment
1b. Entry
2. Uncoating
3-5 production of viral proteins and replication of viral genome
6. Assembly
7. Release

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24
Q

What is viral protein synthesis completely dependent on?

A

Cellular translation via ribosomes - this means all viral genomes must produce mRNA to express the viral proteins

25
Q

The route to produce viral mRNA depends on the what of each virus?

A

It depends on the genome structure of each virus

26
Q

Viral mRNA is produced by transcribing the genome with what? (2)

A

Host RNA polymerase

or Viral RNA polymerase

27
Q

Do large or small DNA viruses use host cell enzymes to replicate?

A

small viruses (e.g. papilloma)

28
Q

Do large or small DNA genome viruses encode many of the enzymes they need i.e. they are more autonomous?

A

Large viruses (e.g. pox viruses, herpes)

example of enzyme: DNA-dependent RNA polymerase

29
Q

Viruses with which type of genome tend to encode their own RNA-dependent RNA polymerase?
What does it use as a template?

A

RNA genome viruses

They use complimentary RNA as a template

30
Q

What do retroviruses use to replicate/synthesise genomes?

A

They use reverse transcriptase

they use this to copy +ve ssRNA into dsDNA - this acts as a new template for protein and genome synthesis

31
Q

What is required/what cells are required for viral propagation? (4)

A

ribosomes for translation of viral mRNA

Enzymes - for replication of genome and assembly of new virions

Transport pathways to reach sites of replication, viral assembly etc.

Energy source

32
Q

What family of viruses is hep B part of?

A

Hepadnaviridae

33
Q

Varicella-zoster virus belong to which family of viruses?

A

Herpesviridae

34
Q

Hep B virus - does it have a DNA or RNA genome?

A

DNA

35
Q

How is hep B transmitted?

A

It is a blood-borne virus

36
Q

In what continents may you be likely to find persistent hep B carriers - and what are these people at risk of?

A

Asia & Africa

Risk of chronic hepatitis, cirrhosis and hepatocellular carcinoma

37
Q

What conditions are caused by the varicella-zoster virus? (2)

A

Chicken pox

Shingles

38
Q

What family of viruses does polio belong to?

A

Picornaviridae

39
Q

Is polio a DNA or RNA virus?

A

RNA

40
Q

Influenza A and B belong to which family of viruses?

A

Orthomyxoviridae

41
Q

Mumps and measles belong to which family of viruses?

A

Paramyxoviridae

42
Q

Name 2 viruses that are from the retrovirus family

A

HIV 1

HIV 2

43
Q

Give an example of a family of large-size RNA viruses

A

Paramyxoviridae (e.g. mumps, measles)

100-130nm diameter

44
Q

Give an example of a family of small-size RNA viruses

A

Picornaviridae

24-30nm diameter

45
Q

Is coronaviridae an RNA or DNA virus?

Is it helical or icosahedral?

Is it enveloped or non-enveloped?

A

RNA

Helical

Enveloped

46
Q

How can viral infections be diagnosed by a lab?

A

Detect virus/viral components: nucleic acid amplification technology (NAT), antigen detection, culture, electron microscopy

Detection of virus-specific antibody responses by serological technique

47
Q

What is viral tropism?

A

It is the ability of a given virus to be able to productively infect a particular cell, tissue or host species

48
Q

What restricts the virus to only being able to infect certain cell types?

A

They need a specific cell receptor on the cell surface. This receptor interacts with proteins on the virus surface

49
Q

How do non-mediated viruses mediate attachment to host cell?

A

Via external capsomere proteins

50
Q

What is the virus receptor for the SARS-CoV-2 virus?

A

ACE2

51
Q

Describe the stages of an acute viral infection (6 steps)

A
  1. Infect host
  2. Establish focus of infection (at site of infection/inoculation)
  3. Overcome host defences
  4. Spread from initial focus
  5. Further replication
  6. Exit from the host (in sufficiently large numbers to infect other hosts)
52
Q

The site of acute viral infection can be ….. (2 potential answers)

A

Superficial

or systemic

53
Q

Describe a superficial viral infection (3)

A

Replication in epithelium at portal of entry (e.g. rhinovirus/common cold, influenza, noroviruses)
Short incubation period (2-4 days)
Acute infection of short duration

54
Q

Outline systemic viral infections (3)

A

Complicated traffic of virus during long incubation period (~2 weeks)

Replication of virus at multiple sites

Natural infection > lifelong immunity e.g. measles, mumps, polio

55
Q

Following from a viral infection/incubation period - which antibody would you expect to peak?

A

IgM (in clinical disease)

Use PCR

56
Q

Following from a viral infection, so during the convalescence stage - which antibody would you expect to peak?

A

IgG (test using serology)

57
Q

What are the 3 potential outcomes following a viral infection?

A
  1. Clearance following acute phase of cell death e.g. flu, polio, measles, viral gastroenteritis
  2. Persistent infection with continued production of infectious virus and immune evasion e.g. hep B, HIV
  3. Latent infection with virus persistence after initial clearance, and asymptomatic or symptomatic reactivation e.g. herpes simplex, varicella zoster
58
Q

Outline the characteristics of a latent viral infections (4)

A

Viral DNA persists but doesn’t replicate to produce new infectious virus

May never causes signs of disease

May activate on one or more occasion and be asymptomatic or cause disease.

Some latent infections may lead to malignant disease.

HHAD: Microbiology (6 decks)

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