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Patho > Viruses > Flashcards

Viruses Flashcards

1
Q

What are the four main characteristics of viruses?

A
  1. small in size - average virus size = 100nm
  2. obligatory intracellular parasites = require living host cell to multiply
  3. must chemically interact with specific surface cell receptors
  4. viruses have a host range
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2
Q

What is a host range?

A

The organisms/hosts a virus has an affinity for - what a virus can infect based on it’s capsid structure

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3
Q

What is tissue tropism?

A

The affinity of a virus for a certain cell or tissue type

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4
Q

What it the most common disease-causing virus?

A

Influenza

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5
Q

What is the normal microflora size in humans?

A

380 trillion viruses

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6
Q

What is the nucleocapsid?

A

The capsid and nucleic acid of a virus

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7
Q

What is a capsid?

A

A protective protein coat that surrounds a viruses genetic material

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8
Q

What are capsomeres?

A

The smaller units that make up the capsid

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9
Q

What are the 4 different shapes a virus can take?

A
  1. helical
  2. polyhedral
  3. spherical
  4. complex
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10
Q

What is the nucleic acid? What are the two types of nucleic acids?

A

The element of the virus that contains the viral genome – can only contain one kind of nucleic acid, either RNA or DNA

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11
Q

What are some characteristics of nucleic acids?

A
  • can be single stranded or double stranded (double has more stability)
  • can be linear or circular
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12
Q

How does the genome size differ between DNA and RNA?

A

DNA has a large genome so it’s less dependent on the host
RNA has a small genome so it’s highly dependent on the host

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13
Q

How does the replication rate vary between DNA and RNA?

A

DNA has a slow replication rate due to it’s large size
RNA has a fast replication rate due to it’s small size

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14
Q

How does the occurrence of mutations vary between DNA and RNA?

A

DNA has low occurrence of mutations
RNA has higher occurrence of mutations
**Transcription error affected by rate of replication

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15
Q

What is the envelope of a virus?

A

A lipid or glycoprotein covering that’s derived from the host cell’s membrane

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16
Q

What are the 3 main proteins that make up the virus envelope and what are they responsible for?

A
  1. envelope proteins
  2. spike proteins
  3. membrane proteins
    ** responsible for binding to receptor sites on the host cell
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17
Q

What is virulence?

A

The ability of a virus to cause harm to the host - affected by variety of factors

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18
Q

How does a virus envelope affect virulence?

A
  • Enveloped viruses are less virulent
  • Non-enveloped viruses are more virulent because they result in cell lysis as they exit the host cell
19
Q

How does a virus envelope affect its resistance to extreme conditions?

A

*extreme conditions: heat, cold, dry, pH, alcohol/disinfectants
- Enveloped viruses have low resistance = easier to destroy outside of the body
- Non-enveloped viruses have high resistance

20
Q

How does the virus envelope affect recognition by the immune system?

A
  • Enveloped viruses are harder for the immune system to recognize
  • Non-enveloped are easier (think less clothing)
21
Q

What are some examples of enveloped viruses?

A

Influenza, RSV, coronaviruses, HIV

22
Q

What are some examples of non-enveloped viruses?

A

Norovirus, adenovirus, rhinovirus

*most GI-infecting viruses are non-enveloped (can withstand stomach pH)

23
Q

What are five factors used to classify viruses?

A
  1. Genome type
  2. Capsid structure
  3. Presence of envelope
  4. Type of host it infects
  5. Mode of action/replication
24
Q

Why do viruses require a host cell to replicate?

A
  • have no metabolism
  • lack enzymes needed for protein synthesis and ATP generation
25
Q

What are the steps of viral replication?

A
  1. Binding and attachment
  2. Fusion
  3. Uncoating
  4. Reverse transciptase
  5. Integration
  6. Transcription
  7. Translation
  8. Budding
26
Q

Explain the binding and attachment step of viral replication.

A

The viruses binding sites attach to the complementary sites on the host cell’s surface

27
Q

Explain the fusion step of viral replication.

A

The virus envelope fuses with the host cell’s membrane - allows the viral RNA and enzymes to enter the cytoplasm

28
Q

Explain the uncoating step of viral replication.

A

The virus uncoats the capsid and releases the viral genetic information into the host cytoplasm

29
Q

Explain the reverse transcriptase step of viral replication.

A

The reverse transcriptase enzyme copies the virus’s single-stranded RNA then copies in reverse to make another mirrored copy = this creates double-stranded DNA

30
Q

Explain the integration step of viral replication.

A

The new viral DNA enters the host cell nucleus where the integrase enzyme facilitates integration of the viral DNA into the host chromosome
– viral DNA now a provirus - either remains latent or is transcribed into RNA

31
Q

Explain the transcription step of viral replication.

A

Proviral DNA cannot leave the nucleus so it’s transcribed into messenger RNA (mRNA) then transported to the host cell ribosome

32
Q

Explain the translation step of viral replication.

A

mRNA is translated into viral proteins using the host cell ribosome
Protease enzyme processes and assembles the new proteins into the new virion
** may remain latent in vacuoles or are released from the cell

33
Q

Explain the budding step of viral replication.

A

Virion buds out of the cell using the plasma membrane of the infected cell to create it’s envelope
** virus is now capable of infecting other cells

34
Q

What are the 3 enzymes involved in viral replication and what are their roles?

A
  1. Reverse transcriptase: copies the RNA to create viral DNA
  2. Integrase: facilitates integration of viral DNA into the host chromosome
  3. Protease: processes and assembles the newly created viral polypeptides into the new virion
35
Q

What are the 6 steps of the chain of infection?

A
  1. Infectious agent
  2. Reservoir
  3. Portal of exit
  4. Mode of transmisison
  5. Portal of entry
  6. Susceptible host
36
Q

What are the phases of virus disease course?

A
  1. Exposure to virus
  2. Incubation stage
  3. Prodromal/infectious stage
  4. Acute stage
  5. Recovery - convalescence and resolution
37
Q

Explain the exposure stage of the virus disease course.

A

Individual is exposed to the virus - enters the body via the respiratory system

38
Q

Explain the incubation stage of the virus disease course.

A

Where the virus invades the host cells and begins replicating
- person is asymptomatic
- time period: 1-3 days

39
Q

What factors influence the time period of the incubation stage?

A
  1. Health of the host
  2. Virulence of the virus
  3. Size of the innoculum (how much virus enters the body)
40
Q

Explain the prodromal or infectious period of the virus disease course.

A

Time where infected person is contagious
Begins ~24 hours prior to symptoms appearing and lasts 3-5 days following onset of symptoms

41
Q

Explain the acute phase of the influenza disease course.

A
  • respiratory symptoms – runny nose, cough, sore throat
  • constitutional symptoms – fever, fatigue, malaise, chills
  • complications – secondary infections (sinus + ear infections, pneumonia), death
42
Q

Explain the convalescence period of the virus disease course.

A

When the immune system contains the virus and is progressively eliminated from the body – repair of damaged tissues, dissipating symptoms
time period: a few days to 1 week or more

43
Q

What factor affects the length of the convalescence period?

A

The health of the individual prior to infection

44
Q

Explain the resolution phase of the virus disease course.

A

Total elimination of virus from the body
- no residual symptoms, total return to health

Patho (9 decks)

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