Microbiology - Part 3 (Virus) Flashcards
What is range of diameter of virus
20-220nm
only visualised by electron microscope
What is diameter of staphylococci bacteria
1 micro m
Are samples from sterile sites needed to diagnose a viral infection?
No as there are no commensal viruses to confuse with
What genetic material is found in a virus?
One type of nucleic acid, RNA or DNA
What surrounds a virus? (not cell wall)
Outer protein coat
Surrounded by a lipid envelope (in some viruses)
- contains viral proteins and lipids
What are purpose of proteins on virus surface?
Allow attachment to complementary receptors on susceptible host cell plasma membrane
What are 6 stages of virus replication?
Attachment Cell entry Interaction with host cells Replication Assembly Release
Describe stage of virus replication: Attachment
Virus receptor binds to cell receptor
Name receptors involved in attachment of HIV to T-cell (virus replication)
gP160 made of gP120 and gP41 (glycoproteins on HIV molecule) allow it to dock and fuse onto CD4 and CCR5 receptors
Describe stage of virus replication: Cell entry
Only the viral ‘core’ which carries the nucleic acid and some associated proteins acting as enzymes for replication and negation of intracellular host defence factors are freed into the host cell cytoplasm.
Outer protein coat does not enter.
Describe stage of virus replication: Interaction with host cells
Virus uses cell materials (enzyes, amino acids, nucleotides) for their own replication.
Also needs to subvert host cell defenses.
Describe stage of virus replication: Replication
Production of progeny viral nucleic acid and viral proteins in nucleus, cytoplasm or both
Where does Assembly stage of viral replication occur
Can occur in:
Nucleus, Cytoplasm, Cell membrane
Give example of virus that assembles in the host cell nucleus
Herpesvirus
Give example of virus that assembles in the host cell cytoplasm
Polio virus
Give example of virus that assembles in the host cell membrane
Influenza virus
Give examples of how virus releases from infected host cell after replicating inside
By bursting cell open (lysis)
By exocytosis/leaking from cell overtime
Only afew particles will enter the host but millions will exit due to replication
Give example of a virus that releases from cell by bursting cell open (lysis)
Rhinovirus
Give example of a virus that releases from cell via exocytosis/leaking
HIV
Influenza (2-3 days from upper respiratory tract)
Decrease different ways in which viruses can cause disease
Damage by destruction of host cells
Damage by modification of host cell structure or function
Damage involving ‘over-reactivity’ of the host as a response to infection - immunopathological damage
Damage through cell proliferation and cell immortalisation (cancer)
Evasion of both extracellular and intracellular host defences
Give example of viruses that causes damage by direct destruction of host cells
Polio
Influenza (respiratory cells)
HIV (immune cells)
How many types of polio are there?
3 but type 1 is most severe
How does polio virus cause direct damage to body?
Enters body orally then invades and replicates in the gut
Then travels in the bloodstream and targets the brain where it results in direct brain cell destruction.
Once infection reaches brain in un-immunised person, it is hard to treat and can result in paralysis.
By time immune response is in effect, the virus has already caused damage.
How can we control polio virus
Vaccination
What cells are most damaged in influenza infection?
Respiratory cells
What cells are most damaged in HIV infection?
Immune cells (CD4+ T cells)
Give examples of viruses that cause damage to host by modification of host cell structure or function
Rotavirus or HIV
(physical or functional modification)
RSV - Respiratory Syncytial Virus (functional modification)
Describe the pathogenesis of rotavirus infection
After ingestion, rotavirus infects epithelial cells of SI (mainly jejunum). Rotavirus are resistant to acid pH.
Causes atrophy and shortening of villi, flattening of epithelial cells and stripping of the microvilli, decreasing SI SArea.
Limits production of digestive enzymes such as those for disaccharides (normally synthesised by cells of brush border).
Patient suffers a malabsorptive state in which dietary nutrients such as sugars are not absorbed by the SI.
Results in Hyperosmotic effects causing profuse Diarrhoea.
How can you treat Rotavirus hyperosmotic effects
Prevent profuse diarrhoea by Fluid Replacement Therapy.
If caught early it is treatable
Give example of viruses that cause damage to host be causing overreactivity of the host as a response to infection (immunopathological damagae)
Hepatitis B and C
HIV
Are majority of infections with Hepatitis B virus symptomatic or asymptomatic
Majority of HBV infection are asymptomatic.
Ig you recover (most do) you will still be a carrier and 80% will be asymptomatic
How are Hepatitis B and C virus spread
By blood or sexual contact
Describe symptomatic infection by Hepatitis B virus
Massive antibody and cell mediated immune responses that destroy many virally infected hepatocytes.
Results in in extensive liver damage.
What is difference between Hepatitis B acute and chronic infections
In acute infection, large numbers of infectious HBV particles are produced and released
In chronic HBV carrier, there is a steady state between virus replication in host cells and host defence responses.
Describe the chronic infection that can result from HBV and the steady-state
Steady state between virus replication in host cells and host defence responses.
Limited but sustained viral replication.
Natural hepatocyte regeneration and get proliferation of hepatocytes due to the oncogenic properties of HBV.
Liver cell destruction by CD8+ T cells that recognise HBV proteins on hepatocyte surface as foreign.
No clinical symptoms but HBV particles circulate in patients bloodstream.
Why does chronic HBV infection cause proliferation of hepatocytes
due to oncogenic properties
What type of lymphocyte recognises HBV proteins on surface of hepatocytes
CD8+ T cells
Give example of virus that causes damage through cell proliferation and cell immortalisation (cancer)
Human papillomavirus
HPV
How does HPV cause damage through cell proliferation and cell immortalisation e.g. Cervical carcinoma
Cervical carcinoma most common HPV cancer
Result of HPV infection of SUPRA BASAL LAYER in genital tract. Here the virus may partially replicate including transcription and expression of several early viral gene products.
At some point the HPV genome may integrate into host cell chromosome.
Following integration, control of viral gene expression by the HPV E2 protein is lost and the HPV E6 and E7 proteins may be expressed.
HPV E6 and E7 proteins prevent the operation of two cell growth and proliferation suppressor proteins - Retinoblastoma (Rb) and p53.
Excessive cell growth and proliferation occurs and cervical carcinoma can result.
How many types of HPV are there and what types have oncogenic properties in humans
70-80 different viruses
Type 16 and 18 have oncogenic potential in humans - responsible for cervical carcinoma
Describe features of HPV virus as a particle
Very small
No envelope
can result in cancers
What increase chance of HPV genome integrating into the host cell chromosome
Mutagenic agents like nicotine
Following integration of HPV genome into host cell chromosome, what proteins are expressed and which are surpressed
Control of viral gene expression by the HPV E2 protein is lost
HPV E6 & E7 proteins are expressed
Following integration of HPV genome into host cell chromosome, what is function of newly expressed HPV E6 and E7 proteins
Prevent the operation of two cell growth and proliferation suppressor proteins - Retinoblastoma (Rb) and p53
What layer of genital tract is initially infected by HPV
Supra basal layer
Certain viruses can evade extracellular and/or intracellular host defences. Which viruses can persist in the body
Herpes virus
Hepatitis B and C viruses
Measles virus
HIV
Certain viruses can evade extracellular and/or intracellular host defences. Which viruses can undergo variation of their surface proteins (antigens), allowing them to evade the specific immune defences of the host?
Influenza
HIV
Hepatitis C
Rhinovirus
How does Influenza achieve variability and hide itself from immune system?
Variation through gene reassortment and mutation causing variation in antigens.
How does HIV achieve variability and hide itself from immune system?
Via variation through gene reassortment and mutation causing antigenic variability and variation through the formation of ‘quasi-species’.
Prevents apoptosis also.
How does Hepatitis C achieve variability and hide itself from immune system?
Variation through the formation of ‘quasi-species’
How does Rhinovirus achieve variability and hide itself from immune system?
Variation through many stable serotypes (about 110 different cold viruses)
Describe effects of EBV (Epstein-Barr virus)
Causes glandular fever, remains latent in B cells meaning you carry virus for rest of life and can transmit via oral secretions.
What viruses undergo persistence or latency to evade host defences
All herpes viruses (HSV - 1 and 2)
Varicella-zoster virus (VZV)
Epstein-barr virus (EBV)
What viruses can prevent host cell apoptosis?
Herpes virus
HIV
What is estimated number of people with HIV infection in UK and of those, what % were unaware of their infection
90,000
13% unaware
How is HIV transmitted
Blood
Sexual
Vertical (Mother to child)
What is PEP
Post exposure prophylaxis
28 days given in combination with ART
What is PrEP
Pre-exposure prophylaxis
How can we prevent HIV spread
Appropriate sex education Reduce frequency of partner change Avoid concomitant sexual partners Reduce high risk sexual practises Consistent condom usage