Intro to Medical Virology

Question 1

Can negative sense ssRNA undergo protein synthesis?

Answer 1

No, must be converted to positive sense first

Question 2

DNA Viruses that infect humans

Answer 2

ssDNA: Parvoviridae

dsDNA: Papovaviridae, Adenoviridae, Herpesviridae, Poxviridae, Hepadnaviridae

Mnemonic: HHAPPPy

Question 3

dsRNA virus family

Answer 3

Reoviridae

Question 4

-ssRNA virus families

Answer 4

Paramyxoviridae, Rhabdoviridae, Bunyaviridae, Filoviridae, Orthomyxoviridae, Arenaviridae

Mnemonic: Paralyzed, Rabid Bunnies Fill Our Arenas

Question 5

+ssRNA virus families

Answer 5

Retrovirus, Togavirus, Flavivirus, Coronavirus, Hepevirus, Calicivirus, Picornavirus

Mnemonic: I went to the Retro Toga party, where I drank Flavored Corona and ate Hippy California Pickles

Question 6

How do cells replicate RNA viruses?

Answer 6

Cells CANNOT replicate RNA. RNA viruses must encode an RNA-dependent RNA polymerase

Question 7

Three types of Viral Capsids

Answer 7

Helical (e.g. Tobacco Mosaic Virus), Icosahedral (e.g. Polio Virus), Complex (e.g. Smallpox (variola))

Question 8

Naked Capsid Properties

Answer 8

Non-envoloped; Capsid is made of protein is very stable

• Stable to: temperature, acid, proteases, detergents, drying
• Released by cell lysis

Question 9

Naked Capsid Clinical Consequences

Answer 9

Spread easily
Dry out and remain infectivity
Survive adverse conditions of the gut
Resistant to detergents and poor sewage treatment

Question 10

Envelope Properties

Answer 10

Lipid envelope; not as stable as protein

• Envrionmentally labile and disrupted by: acid, detergents, drying, heat
• Released by budding and cell lysis

Question 11

Envelope Clinical Consequences

Answer 11

• MUST STAY WET*
• Cannot survive GI tract
• Spreads in large droplets, secretions, organ transplants, and blood transfusions
• Does not need to kill the cell to spread

Question 12

Virus Life Cycle Summary (6 steps)

Answer 12

1. Attachment
2. Entry
3. mRNA production
4. Protein and Genome synthesis
5. Virion Assembly
6. Egress

Question 13

Attachment and Entry

Answer 13

Penetration: a direct fusion event

Entry: viral attachment proteins can be used to hijack vesicular transport system of cells –> invagination of plasma membrane –> pH change causes release of capside into cell
***Can occur in both enveloped and non-enveloped viruses

Question 14

How do viruses get around the fact that cellular DNA replication machinery is not available at all times?

Answer 14

1. Make cellular DNA replication machinery available (e.g. PAPOVAVIRUSES stimulate cell growth and DNA synthesis)
2. Encode viral proteins to synthesize genome (e.g. POXVIRUSES encode their own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis, replication machinery, and transcription machinery in the cytoplasm)

Question 15

(+)ssRNA viruses vs. (-)ssRNA virsues: dealing with the challenge of having no RdRp

Answer 15

(+)ssRNA viruses: encode a RdRp in your geneome

(-)ssRNA viruses: encode a RdRp in your genome AND carry the enzyme in your virion

Question 16

What is the general pathway to viral assembly and egress?

Answer 16

1. Individual viral proteins form into capsid subunits
2. Subunits combine to form complete capsid
3. Viral genome and other essential virion components are selectively packaged into capsids
4. Envelope acquired (only for enveloped viruses)
5. Virus exits cell
6. Virions mature (only for certain viruses)

Question 17

Budding

Answer 17

Allows viruses to assemble and get out of the cell at the same time

Question 18

Egress: Lysis

Answer 18

***KILLS the cells as the virions leave

Lysis often accompanies release of virions with naked capsids

Question 19

How do viruses evolve or change? (3 ways)

Answer 19

1. Recombination
2. Reassortment
3. Point mutations

Question 20

Plaque Assay

Answer 20

• Place virus sample on a monolayer of cells, allowing for infection
• Lets you know infectious virus particle is there and allows you to count the number of viruses (each plaque is caused by one particle)

Question 21

Which Viral Diagnostic test(s) target Antibodies?

Answer 21

ELISA

Western Blot

Question 22

Which Viral Diagnostic test(s) target Genomes?

Answer 22

DNA: PCR
RNA: RT-PCR

Question 23

Which Viral Diagnostic test(s) target Viral Antigens?

Answer 23

ELISA

Others

Question 24

Which Viral Diagnostic test(s) target Infectious Virions?

Answer 24

Plaque Assay

Question 25

Virus Culture/Plaque Assay (Detects, Advantages, Limitations)

Answer 25

D: Infectious Virus
A: Positivity shows viral infection
L: Restricted to viruses that replicate in tissue culture and produce cytopathic effect

Question 26

Electron Microscopy (Detects, Advantages, Limitations)

Answer 26

D: Virion Particles
A: Especially helpful in the identification of emerging viruses
L: Relatively expensive and technically challenging

Question 27

Antigen Detection (e.g. ELISA) (Detects, Advantages, Limitations)

Answer 27

D: Viral proteins and glycoproteins
A: Sensitive and quick
L: Requires specific antibody

Question 28

PCR (Detects, Advantages, Limitations)

Answer 28

D: DNA genomes
A: Highly sensitive
L: DNA sequence information must be available

Question 29

RT-PCR (Detects, Advantages, Limitations)

Answer 29

D: RNA genomes
A: Highly sensitive
L: RNA sequence information must be available

Question 30

Serology (e.g. Western Blot) (Detects, Advantages, Limitations)

Answer 30

D: Anti-viral Antibodies
A: Sensitive and quick
L: Time must be allowed for the initiation of the immune response. Care must be taken to differentiate present from past infections.