Virology Flashcards
What info does the genome need encoded?
- 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
What is the difference between +ve and -ve sense ssRNA?
+ve can encode straight away while -ve must be converted to +ve first
What are ds DNA viruses?
Poxvirus
Herpesvirus
papilliomavirus
addenovirus
What are ds RNA viruses?
Reovirus
What are ss DNA viruses?
parvovirus
What are ds RNA viruses with a RNA intermediate?
hepadenaviridae
What are -ve sense ss RNA viruses?
orthomyxovirus
paramyxovirus
rhabdovirus
What are +ve sense ss RNA virsues?
calicivirus
coronavirus
flavivirus
What are ss RNA viruses with a DNA intemediate?
retrovirus
What is the function of viral proteins?
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
What is the capsid made of?
capsomer subunits
What is the function of the capsid?
packaging the genome and essential enzymes, protection from nucleases and UV light
What are the different ways viral proteins can be packaged?
icosohedral symmetry
helical
complex
What viruses have a lipid bilayer?
many icosohedral symmetry viruses and most helical
What ways can a virus enter the body?
Respiratory
Oral
Cutaneous
percutaneous injection
sexually transmitted
What happens in lytic infection?
- 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)
What happens in latent infection?
- 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
What is the significance of a persistant infection?
- different to latent as cells continually make and shed new viruses
- associated with immune system failure to clear a viral infection
What is the inflammatory response to a viral infection?
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
How does a fever form?
- 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
What are examples of sickness behaviour?
- decreased motor activity
- Social withdrawal reduced responsiveness
- Reduced food and water intake
- Increased slow-wave sleep
- Altered cognition
- Increased pain sensitivity
How are sickeness behaviours mediated?
pro-inflammatory cytokines on the CNS released in response to pathogen-associated molecular patterns (PAMPs)
How does FMD infect the host cells?
-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
What are the concequences of FMD on the host animal?
-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)
What are the 6 phases of a plaque assay?
Inoculation
Virus attachement
Uncoating
Eclipse phase
virus assembly
cell lysis
What happens during uncoating?
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
What happens during the eclipse phase?
new virus proteins and nucleic acids are being synthesised. No infectious virus particles can be detected
What is a summery of virus replication?
- 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
What region of the mRNA encodes proteins?
Open reading frame
How do you convert +ve sense ssRNA into +ve mRNA?
- 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
