Viruses Flashcards
Which are bigger, bacteria or viruses?
Bacteria (1μ) in comparison to viruses (20-220nm)
Give two main differences between bacteria and viruses
- Viruses only grow inside living cells
2. Viruses have no cell wall
Where does the assembly of viruses take place in a cell?
Can take place anywhere. Nucleus (herpes virus), cytoplasm (poliovirus) or cell membrane (influenza)
Give two methods of release of a virus from a cell
- Lysis of the cell (rhinovirus)
2. By exocytosis over time (HIV, flu)
There are 5 main ways that viruses cause disease. What are they?
- Damage by direct destruction of host
- Damage by modification of host cell structure or function
- Damage through ‘over-reactivity’ of the host as a response to infection
- Damage through cell proliferation and immortalisation
- Evasion of extracellular/ intracellular host defence (variability or persistence)
Rotavirus is an example of a virus that causes disease by modification of the host cell. How does it do this?
- Infects epithelial cells of small intestine (jejunum) and shortens and atrophies villi
- This means there is decreased SA for absorption
- Also limits production of digestive enzymes e.g. disaccharides
- Malabsorptive state in patient and produces hyperosmotic effect in the jejunum causing profuse diarrhoea
Are the majority of hep B infections symptomatic or asymptomatic?
Asymptomatic
Why do carriers of HBV show no clinical symptoms?
They maintain a steady state between virus replication in host cells and host cell response
- Limited but sustained viral replication
- Proliferation of hepatocytes due to oncogenic properties of HBV
- Natural hepatocyte regeneration
- Liver cell destruction by CD8+ T cells that recognise HBV proteins on cell surface as foreign
How many types of HBV virus are there and how many have oncogenic potential in humans?
70-80 types. Type 16 and 18 have oncogenic potential
How does HPV cause a cervical cell carcinoma?
HPV genome integration disrupts E2 viral gene protein (control lost) which prevents the control of E 6 and 7. These control two cell growth and proliferation suppressor proteins Rb (E7) and p53 (E6), leading to dysplasia and cervical cell carcinoma.
What can increase the chance of integration of HPV virus into genome?
Mutagenic agents such as nicotine
How do viruses evade host defences (at cellular level)?
a) Persistence/latency (carrier for rest of your life)
b) Cell-to-cell spread (evade extracellular responses eg Ab’s)
How do viruses evade host defence (at molecular/genetic level)?
a) Antigenic variability
b) Prevention of host cell apoptosis
c) Down regulation of interferon and other intracellular host defence proteins (most)
d) Interference with host cell antigen processing pathways
Outline the 5 stages of chicken pox
Macule, papule, vesicle (blister formation), pustule, scab
What are ‘cropping lesions’ and what virus do they relate to?
Are lesions at different stages of evolution on the same body part. Found in chickenpox
What virus causes chickenpox and what kind of virus is this?
Varicella zoster - is a herpes virus
What transmission rate does chickenpox have?
90%
How long before the onset of rash in chickenpox is an individual infectious?
2 days (normally when symptoms start)
How is chickenpox spread?
Airbourne (nasal pharynx replication)
-normally from face –> face contact or being in the same room for more than 15 mins
In what two groups of people is it important to try and prevent chicken pox?
Pregnant and immunosupressed
Looking at the rash, how can you distinguish between chickenpox and smallpox?
Chickenpox will divide in warm parts of the body (core), whereas small pox will divide in the cooler areas (extremities)
What doubles the risk for pneumonitis in a patient with chicken pox?
If they are a smoker/ have lung disease
What virus causes shingles?
Herpes zoster
Why does shingles occur?
After primary infection, herpes zoster remains dormant in dorsal root ganglia. Reactivation causes shingles