An Introduction to Viruses Flashcards
What can you say about the size of viruses?
They are very small, being only 20-400nm in diameter
What can you say about cells, viruses and replication?
Viruses are non-cellular so genetic elements cannot replicate independent of a host
What are different structures of viruses?
Icosahedral (20 faces, each in an equilateral triangle)
Helical (protein binds round DNA/RNA in a helical fashion)
Complex (neither of above)
What can you say about the host range of viruses?
Many viruses have a specific host range and can only infect specific host cell types
Can viruses be grown in a lab dish?
No, because they need a cell to act as a host
What are examples of icosahedral viruses?
Polio
Rhino
Adeno
What is an example of a helical virus?
Tobacco mosaic virus
What is a virus?
Genetic element that cannot replicate independently of a living (host) cell
What is virology?
The study of viruses
What is a virion?
Extracellular form of a virus
Where do virions exist and what do they do?
They exist outside of the host and facilitates transmission from one host cell to another
What do virions contain?
Nucleic acid genome surrounded by a protein coat and in some cases other layers of material
What are virus families classified according to?
Virion shape/symmetry
Presence/absence of envelope
Genome structure
Mode of replication
What do envelopes do to a virus?
Makes them much more fragile, making them easier to kill and cannot survive outside the body for a long time
What are examples of enveloped viruses?
Flu
HIV
Hep C
Where are lipid envelopes stolen from?
The host cell the virion came out of
What is the process of virus replication?
1) Replication of genomic nucleic acid
2) Virion assembly
3) Virion released from cell and attaches to another
4) Uncoats inside the other cell
5) Replication of genomic nucleic acid
What are different kinds of transmission?
Blood borne
Sexual
Vertical
Faecal-oral
Droplet
Airborne
Close contact
Vector borne
Zoonotic
What can you say about the kinds of animals viruses can infect?
Some viruses can only infect humans whereas some can infect a range of animals, leading to recombination and generation of new strains
What does viruses infecting many kinds of animals lead to?
Recombination and generation of new strains
What are the possible consequences of viral infection?
Clearance of virus (no short or long term immunity)
Chronic infection
Latent infection (virus lies dormant)
Transformation (long term infection with altered cellular gene expression)
What happens when viruses lie dormant?
Full virus genome is retained in the host cell but expression is restricted, but reactivation may occur
What are examples of viruses that can lie dormant?
Herpes simplex virus
Varicella zooster virus
How can viruses lead to cancer?
Modulation of cell cycle control (driving cell proliferation)
Modulation of apoptosis (prevention of programmed cell death)
Reactive oxygen species damage (causes inflammatory response which lead to cancer via oxygen species)
What aspects of a virus can be detected?
Whole organism
Part of organism (such as antigen or nucleic acid)
Immune response to a pathogen (such as an antibody)
What can the whole organism be detected by?
Microscopy
Culture
What is not really used anymore?
Electron microscopy and cell culture
Why is cell culture not practical?
Works well but has a large time lag
What can looking at the immune response determine?
Acute/recent infection
Prior infection/response to vaccination
What does virustatic mean?
Stopping the growth of viruses
What are all antiviral agents?
Virustatic
Why are there limited viral proteins for antiviral agents to target?
Because viruses utlilise a host cells enzymes
What may antiviral agents be used for?
Prophylaxis (to prevent infection)
Pre-emptive therapy (evidence of infection is detected but before symptoms are present)
Overt disease
Suppressive therapy (keep viral replication below the rate that causes tissue damage)
What is prophyaxis?
To prevent infection
What is pre-emptive therapy?
When there is evidence of infection but before symptoms are present
How can viruses be prevented?
Immunisation (vaccination/passive immunisation with immunoglobin)
Prophylactic treatment post exposure
Infection prevention and control measures
Blood/tissue/organ screening
Antenatal screening
What is eradication?
Permanent reduction to 0 of worldwide incidences of infection
What properties do viruses need to have to be eradicated?
No animal reservoir or ability to amplify in the environment
Clearly identifiable
No chronic carrier state
Efficient and practical intervention (such as vaccination)
Political/social support
What is an example of a virus that has been eradicated?
Smallpox
