Viruses 2 Flashcards
Viral replication
- 6 main events
- Attachment to host cell
- Penetration of cell membrane
- Uncoating
- Viral genome replication, transcription + translation
- Assembly of progeny virions
- Release of new virions
Viral replication
- outcomes
- Replication of virus + destruction of host
- Elimination of virus from host w/out obvious damage to host
- Survival of infected cell w/ virus carried in dormant state OR v low levels of replication
- Transformation of host cell + survival of cell in abnormal state
e. g. formation of cancerous cells
Tropism
- depends on
- examples
variation in display of receptors
Papilloma
- tropism for epithelial cells
= express receptors recognised by virus
Ebola
- v broad tropism
- infects many different tissues
Tropism
- also effects..?
- example
limits host range/tissue type/cell type infected
e.g. Polio virus recognises the PVR receptor which mice don’t produce
DNA virus life cycle
-e.g. HPV group 1
- what might occur?
Virus enters cytoplasm + uncoated at nucleus
Viral DNA enters host nucleus
-> transcribed by host RNA pol
Viral mRNA -> cytoplasm
-> translation of viral proteins
Viral DNA may integrate into host genome
-> gene disruption + transformation of host cell into cancerous state
RNA virus life cycle
-e.g. Picornaviruses group 4
Virus replicates in cytoplasm
Viral genome directs cell to produce RNA-dependednt RNA pol
-> converts +ve sense RNA to -ve sense
AND allows production of more copies of +ve sense genome + mRNA
Cell bio machinery translates viral mRNA into protein
RNA retrovirus life cycle
e.g. HIV group 6
virus synthesises RTase (packaged in capsid w/ genome)
viral genome uncoated in cytoplasm
-> RTase makes dsDNA from viral RNA genome
dsDNA moves to nucleus
-> integrates into host genome
replicates silently using host cell machinery
-> produces low levels of new virions w/ little effect on host
immune response
innate barriers
some PRRs (pattern recognition receptors) recognise viral MAMPs (microbe associated molecular patterns)
interferon production
interferons
type 1
- induce production of intracellular proteins
- > inhibit viral replication in host cells
type 2
- activate WBCs involved with infected host cells
immune functions designed to deal w/ infected host cells
detection of viral proteins by infected cells
-> target them for cytotoxic T cells
infected cells may undergo apoptosis
- prevents spread
immune evasion
- mechanism examples
HIV
- produce proteins that inhibit autophagosome formation
Herpes
- suppress apoptosis
- > integrates into genome + remains dormant
immune response
- antibodies can…
bind to virus + prevent attachment to host cell receptors
generate large aggregates of viruses
-> clearance by immune cells
target viruses for phagocytosis
strategies to combat viral infections
identify reservoirs + routes of transmission
-> try to block exposure
vaccination
- use attenuated virus or antigen to stimulate IS
develop antiviral drug
- hard as lack of viral targets
Blocking exposure
- example
Hep A
High level of viral shedding in faeces
transmitted via facecal-oral route
risk inversely proportional to sanitation levels
Vaccination
- example
Influenza A
main surface antigens
= Haemaglutanin + Neuraminidase
new variations arise via antigenic drift OR shift
