Flashcards in Introduction to viruses Deck (18)
classification of viruses
virus families can be classified according to:
-presence/absence of envelope
-mode of replication
complete infective form of a virus OUTSIDE the host
principles of viral culture
cells are inoculated with virus in vitro, the virus repicates within these cells.
-spike projections from envelope
-protein capsid inside lipid envelope
-nucleic acid inside protein capsid
-virion associted polymerase attached to DNA
1. virus binds membrane of host cell
2. virus is uncoated and the viral nucleic acid enters the cell
3. this nucleic acid is replicated to be incorporated into new virions
4. the viral nucleic acid is also transcribed into mRNA which then form proteins for the production of new virions.
5. the replicated viral nucleic acid and viral proteins then combine to form virions which bud off from host cell and mature.
the range of organisms that a virus can infect; some viruses may only infect humans, some may infect animals/birds too.
consequences of a viral infection
-Clearance of virus (with no, short or long term immunity)
Hepatitis C (no lasting immunity)
Measles (long term immunity)
- Chronic infection
HIV, hepatitis B, hepatitis C
- Latent infection
- Transformation (long term infection with altered cellular gene expression)
Epstein-Barr Virus, Human Papillomavirus
following primary infection viruses will lie dormant in host cells. Viral genome will remain in cells but expression will be limited. Reactivation may occur.
mechanisms by which viruses can cause cancers
-modulation of cell cycle
-modulation of apoptosis
-reactive oxygen species mediated damage
modulation of cell cycle
drives cell proliferation
modulation of apoptosis
prevents programmed cell death
Reactive oxygen species mediated damage
persistent viral infections can cause inflammatory processes which lead to cancer via reactive oxygen species)
3 ways in which viruses can be detected
-detecting whole organism (microscopy and culture)
- detecting part of virus (antigen, nucleic acid)
-immune response to a pathogen (antibodies)
all antiviral agents are virustatic, none are virucidal.
when is antiviral therapy used?
-prophyaxis (prevent infection)
-pre-emptive (before symptoms occur but when there is evidence of infection/replication detected)
-overt (plain) disease
prevention of viral infection
-Prophylactic treatment post exposure
-Infection prevention & control measures
-Blood / tissue / organ screening
factors that allow a virus to be eradicated
-No animal reservoir or ability to amplify in the environment
-Clearly identifiable, with accurate diagnostic tool
-No chronic carrier state
-Efficient and practical intervention, e.g. vaccination
-Political / social support