Introduction to Viruses Flashcards
What three categories can viruses be placed into
Icosahedral - have 20 faces with each being an equilateral
Helical - the protein binds around DNA/RNA in a helical fashion
Complex - neither icosahedral or helical
Where do viruses replicate
Inside the host cell as they are obligate intracellular pathogens
Viruses are…
non-cellular and small
How can viruses be classified
Order Family Genus Species (in this order)
What factors are looked at when determining virus families
Virion shape/symmetry
Presence/absence of envelope
Genome structure
Mode of replication
Describe the structure of viruses
They have: Spike projections Lipid envelope Protein caspid Virion associated polymerase Nucleic acid
How do viruses replicate
The viruses undergoes: Maturation Attachment Uncoating Replication of genomic nucleic acid (either through mRNA synthesis or genomic nucleic acid synthesis) Protein synthesis Virus proteins are inserted into the membrane Virion is assembled Budding and release
What is host range in viruses
Some viruses may only infect humans while others can also infect other animals/birds
What can the coinfection of human and animal/bird strains in one organism cause
The recombination and generation of a new strain
What can a viral infection cause
Clearance of a virus with: no, short or long-term immunity
Chronic infection (e.g. HIV, Hep B)
Latent infection
Transformation
What is transformation
Long-term infection with altered cellular gene expression (e.g. EBV)
Give an example of a disease which shows viral latency
Herpes Simplex Virus
Varicella Zoster Virus
What is viral latency
When viruses stay dormant in the host cell after a primary infection.
The full viral genome is present but its expression is restricted
What is reduced in viral latency
Number of viral antigens present
No viral particles produced
Where is reactivation most likely to occur
Immunocompromised patients
How can viruses lead to cancer
By:
Modulation of cell cycle control - to drive cell proliferation
Modulation of apoptosis - prevents apoptosis
Reactive oxygen species mediated damage - some persistent viral infections can cause persistent inflammatory processes which lead to cancer via reactive oxygen species
Give examples of viruses which can lead to cancer
EBV - leading to Hodgkin’s lymphoma, nasopharyngeal carcinoma and post-transplant lymphoproliferative disease
Human herpes virus 8 - leading to Kaposi’s sarcoma, primary effusion lymphoma, Castlemans’s disease
HPV - cervical, anal oropharyngeal cancers
What parts of a virus can be dectected
Whole organism
Part of organism (e.g. antigen, nucleic acid)
Immune response to a pathogen (e.g. antibodies)
How can the whole viral organism be detected
Microscopy
Culture
How can part of the viral organism be detected
Antigen dectection
DNA/RNA dectection
Extraction of genetic material from sample
Amplification of region of target organism genome
What can an immune response be used to determine
An acute/recent infection
Prior infection/response to vaccination
Are antiviral agents virustatic or virucidal
Virustatic
When is antiviral therapy used
Prophylaxis - to prevent infection
Pre-emptive therapy -
when there is evidence of infection/replication but before symptoms begin
Overt disease
Suppressive therapy - to keep viral replication below the rate which causes tissue damage in an asymptomatic infected
How can viral infections be prevented
Vaccinations Passive immunisation with immunoglobulin Prophylactic treatment post exposure Infection prevention and control measures Blood/tissue/organ screening Antenatal screening
What infection prevention and control measure can be put into place
Isolation of symptomatic patients
Personal protective equipment
Safe use and disposal of sharps
Give examples of viruses which can be eradicated
Small pox (eradicated in 1979)
Measles
Polio
What properties do viruses require to potentially be eradicated
They should:
Have no animal reservoir or ability to amplify in the environment
Be clearly identifiable, with accurate diagnostic tools
Have no chronic carrier state
Have efficient and practical intervention, e.g. vaccination
Have political/social support
How are viruses classified
Shape
Presence of envelope
Genome structure
Mode of replication
What cancer is hepatitis B associated with
Hepatocelluar carcinoma
What is S. aureus common cause of
Skin and soft tissue infections
What is group A strep
Beta haemolytic
What is enterococcus faecalis
Gram positive cocci
