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PID Virology > Viral Pathogenesis > Flashcards

Viral Pathogenesis Flashcards

1
Q

How do we classify viruses?

A

By their genome (DNA or RNA), viral characteristics, diseases, target tissue, geographic location (no longer preferred), and the Baltimore system (most commonly used).

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2
Q

How does the Baltimore system classify viruses?

A

By their manner of mRNA synthesis and replication, plus physical and biochemical characteristics such as size, morphology, and type of genome.

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3
Q

What are the 8 steps in viral replication?

A

Recognition, attachment, penetration/entry, uncoating, macromolecular synthesis, assembly, budding, and release.

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4
Q

Which step in viral replication is only present for enveloped viruses?

A

Budding.

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5
Q

What are the functions of viral attachment proteins (VAPs)?

A

To identify specific host cells and bind to their receptors (recognition and attachment).

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6
Q

How do non-enveloped viruses enter cells?

A

Receptor-mediated endocytosis.

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7
Q

How do enveloped viruses enter cells?

A

Fusion of viral and cellular membranes.

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8
Q

How does uncoating differ between non-enveloped and enveloped viruses?

A

Non-enveloped viruses have their capsid removed, while enveloped viruses have their envelope removed.

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9
Q

Once inside a cell, where do DNA and RNA viruses each go to replicate?

A

DNA goes to the nucleus, RNA stays in the cytoplasm.

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10
Q

What is macromolecular synthesis?

A

Synthesis of viral mRNA and proteins.

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11
Q

What do viruses need for macromolecular synthesis?

A

Host machinery (ribosomes, tRNA, and post-translational mechanisms).

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12
Q

What are the 3 different mechanisms for release of virus from a cell?

A

Lysis, budding, and exocytosis.

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13
Q

Single-stranded RNA viruses (ssRNA) can be either a positive strand or negative strand. What is the main difference in how they replicate?

A

+RNA resembles host mRNA, so it is immediately picked up by host ribosomes to start replication. -RNA does not resemble host mRNA, so it must first create its own positive strand to act as a template for replication, using RNA-dependent RNA polymerase. This means that +RNA viruses replicate faster than -RNA viruses.

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14
Q

What is a key feature of retroviruses?

A

They can integrate into the host genome.

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15
Q

Why do RNA viruses have a higher rate of mutation than DNA viruses?

A

Because they utilize RNA-dependent RNA polymerase, which has no proof-reading mechanisms and is highly prone to error.

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16
Q

What are the 3 mechanisms by which viral genomes can evolve, and how are they different?

A

1) Random mutations - small changes in the genome.
2) Recombination - exchange of genetic sequences.
3) Reassortment - exchange of segments.

17
Q

What are the possible results of viral genome evolution? (5 answers)

A

New viruses, quasispecies, defective genomes, changes in virulence, and pseudotype viruses.

18
Q

True or False: Mutations are always beneficial for the virus.

A

False.

19
Q

List and define the different types of mutations. (6 answers)

A

Lethal - virus cannot replicate.
Deletion - loss or selective removal of function.
Plaque mutants - differ from wild type.
Host range mutants - differ in target tissue or species.
Attenuated mutants - cause less severe disease.
Conditional mutants - can replicate only under certain conditions.

20
Q

What is the purpose of homologous or non-homologous recombination?

A

To repair double-strand breaks in DNA.

21
Q

What is reassortment and what types of viruses does it occur in?

A

Exchange of part of the genome. Occurs in all segmented viruses (Influenza, Arenaviruses, Reoviruses, and Coronaviruses). This is the major event giving rise to new pandemics.

22
Q

What is gene amplification/reduction?

A

The process during replication where certain genes are duplicated and modified, so that advantageous mutations are retained.

23
Q

What are the 3 outcomes of cytopathogenesis?

A

Abortive infection (permissive or non-permissive)
Lytic/productive infection
Non-lytic infection

24
Q

What are the 3 different mechanisms of lytic infections?

A

Virus-mediated lysis, apoptosis, and immune-mediated lysis.

25
Q

What are the 4 types of non-lytic infections?

A

Persistent, latent, recurrent, and oncogenic.

26
Q

True or False: The humoral immune response is useless against viral pathogens.

A

False. Both the humoral and cellular immune responses are important in combating viral pathogens.

27
Q

What is the main antiviral response that is responsible for the classical viral symptoms, and which cytokines are involved?

A

Interferon response; IFN-alpha and IFN-beta.

28
Q

What are the 3 local effectors and outcomes of the antiviral state induced by the IFN response?

A

2’5’ oligo A synthase -> RNAse L -> degrades ssRNA.
PKR -> phosphorylates eIF2 -> inhibits protein synthesis.
Mx -> inhibits viral synthesis, sequesters viral proteins, prevents integration.

29
Q

What distant tissues does the IFN response act on?

A

CNS, bone marrow, and lymph nodes/spleen.

30
Q

What factors determine what type of disease a virus will cause? (6 answers)

A

Tissue tropism, permissiveness of cells for replication, portal of entry, access to target tissue, virus strain, and virulence factors

31
Q

What factors determine the severity of disease a virus will cause? (9 answers)

A

Virus strain, cytopathic effects, immune status, immunopathology, inoculum size, prior exposure, general health and nutrition, genetics, and age.

32
Q

What does a short incubation period indicate about a virus?

A

The primary site of infection is the target tissue, and infection of that tissue is what causes the disease symptoms.

33
Q

What does a long incubation period indicate about a virus?

A

The virus must spread from the primary site of infection and be amplified, OR the disease symptoms are causes by immunopathology.

34
Q

What is the simplest way to diagnose a virus in practice?

A

Patient history and symptoms.

35
Q

Why would we perform a lab study on a virus? (5 answers)

A

To identify virus to confirm diagnosis, determine appropriate antiviral therapy, define course of disease, monitor disease epidemiologically, and educate physicians and patients

36
Q

What can we look for on cytology to identify a virus? (6 answers)

A

Cytopathic effects, morphology, lysis, syncytia, inclusion bodies, and immunofluorescence.

37
Q

What can we determine using serology?

A

Virus identity and strain, primary infection or reinfection, acute or chronic disease.

38
Q

What is electron microscopy most useful for regarding viruses?

A

Detecting and identifying viruses in research labs that have characteristic morphology.

PID Virology (1 decks)

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