Virology

Question 1

What info does the genome need encoded?

Answer 1

• replication and efficient expression of genome
• assembly and packaging of genome
• regulation and timing of the reproductive cycle
• modulation of host defences
• spread to other cells and hosts

Question 2

What is the difference between +ve and -ve sense ssRNA?

Answer 2

+ve can encode straight away while -ve must be converted to +ve first

Question 3

What are ds DNA viruses?

Answer 3

Poxvirus
Herpesvirus
papilliomavirus
addenovirus

Question 4

What are ds RNA viruses?

Answer 4

Reovirus

Question 5

What are ss DNA viruses?

Answer 5

parvovirus

Question 6

What are ds RNA viruses with a RNA intermediate?

Answer 6

hepadenaviridae

Question 7

What are -ve sense ss RNA viruses?

Answer 7

orthomyxovirus
paramyxovirus
rhabdovirus

Question 8

What are +ve sense ss RNA virsues?

Answer 8

calicivirus
coronavirus
flavivirus

Question 9

What are ss RNA viruses with a DNA intemediate?

Answer 9

retrovirus

Question 10

What is the function of viral proteins?

Answer 10

Protection of genome
- Assembly of a stable protective shell
- specific recognition and packaging of nucleic acid
- interaction with host cell membranes

Delivery of genome
- Binding to external receptors on host cells
- transmission of signals that frees the genome
- induction of fusion with the host cell membranes

Other
- Viral replication

Question 11

What is the capsid made of?

Answer 11

capsomer subunits

Question 12

What is the function of the capsid?

Answer 12

packaging the genome and essential enzymes, protection from nucleases and UV light

Question 13

What are the different ways viral proteins can be packaged?

Answer 13

icosohedral symmetry
helical
complex

Question 14

What viruses have a lipid bilayer?

Answer 14

many icosohedral symmetry viruses and most helical

Question 15

What ways can a virus enter the body?

Answer 15

Respiratory
Oral
Cutaneous

percutaneous injection
sexually transmitted

Question 16

What happens in lytic infection?

Answer 16

• many acute infections end in cell death - complete loss of cell function and release of new viral particles Cytopathic effect
• Release of virus from one cell can infect 1000s of new cells
• extensive loss of function - loss of mucocilliary clerarance and localised respiratory disease
• general multisystem disease (canine dystemper)

Question 17

What happens in latent infection?

Answer 17

• Virus infection is dormant and not replicating in cells (transcriptional silence) - no cell death
• can persit for lifetime of host
• latently infected animals act as source of infection for others

Question 18

What is the significance of a persistant infection?

Answer 18

• different to latent as cells continually make and shed new viruses
• associated with immune system failure to clear a viral infection

Question 19

What is the inflammatory response to a viral infection?

Answer 19

Virus is detected by pattern recofnition receptors ( → induces inflamatory cytokine (TNF-a, IL-6/12) and type 1 interferon (IFN-a/b) release
- interferons produced are secreted and bind to receptors on cells
- signals synthesis of proteins with antiviral activity

Question 20

How does a fever form?

Answer 20

• infection leads to interferon and TNFa production
• binds to opiod receptors on nerve cells in the hypothalamus
• activates COX-2 leading to increased PGE2
• altered firing rate of temperature sensitive neurones in the anterior hypothalamus

Question 21

What are examples of sickness behaviour?

Answer 21

• decreased motor activity
• Social withdrawal reduced responsiveness
• Reduced food and water intake
• Increased slow-wave sleep
• Altered cognition
• Increased pain sensitivity

Question 22

How are sickeness behaviours mediated?

Answer 22

pro-inflammatory cytokines on the CNS released in response to pathogen-associated molecular patterns (PAMPs)

Question 23

How does FMD infect the host cells?

Answer 23

-FMD enters host by ingestion/inhalation from infected pastures & sets up a primary oro-nasal infection
-FMD attaches to integrins, binding by an RGD (amino acid triplet) motif in the virus capsid protein which mimics the natural ligand on matrix proteins
-Virus spreads from oropharynx (primary infection: first detected on tonsillar crypts, in epithelium) to other sites

Question 24

What are the concequences of FMD on the host animal?

Answer 24

-Causes shutdown of host cell protein synthesis
-Loss of host cell integrity & cell death with lysis (=cytolytic infection) > release of infectious virus
-Virus spreads locally to basal epithelial cells with high integrin expression
-Presence of virus causes inflammatory response both in the epithelium & in adjacent tissues, through influx of immune cells to site of infection
(several round of viral replication needed before macroscopic lesions appear)

Question 25

What are the 6 phases of a plaque assay?

Answer 25

Inoculation
Virus attachement
Uncoating
Eclipse phase
virus assembly
cell lysis

Question 26

What happens during uncoating?

Answer 26

virus enters the cells and releases its nucleic acid into the cell, for this to happen the virus has to be dismantled inside the cell

Question 27

What happens during the eclipse phase?

Answer 27

new virus proteins and nucleic acids are being synthesised. No infectious virus particles can be detected

Question 28

What is a summery of virus replication?

Answer 28

• Attachment to plasma
• Enter into cytoplasm and nucleus
• Un-coating of virus particle
• Synthesis of mRNA and protein
• Replication of nucleic acid
• Virus assembly
• Exit of cell

Question 29

What region of the mRNA encodes proteins?

Answer 29

Open reading frame

Question 30

How do you convert +ve sense ssRNA into +ve mRNA?

Answer 30

• reverse transcriptase copies it into double stranded DNA
• integrase integrates this into the host genome
• the host uses transcription and RNA polymerase to make mRNA