Viruses Flashcards
What are the seven viral groups by Baltimore classification and give an example of each?
1) dsDNA e.g. herpesvirus family
2) ssDNA e.g. parvovirus
3) dsRNA e.g. rotaviruses
4) + sense RNA e.g. HCV, polio
5) - sense RNA e.g. influenza, ebola
6) RNA RT e.g. HIV
7) DNA RT e.g. HBV
What are the 4 courses of viral infection?
Acute - influenza One bump at start. 99% of viral infections are acute, acute and resolving.
Persistent infection, smoldering
Persistent infection, latent e.g. Herpes simplex virus, cold sores
Persistent infection, slow e.g. Measles, HIV
What is the prodromal response to infection?
Most common symptoms of viral infection are due to general effects of innate immune responses. Fever, fatigue, sleep, mobilisation of lymphocytes, acute phase proteins.
What is antigenic drift?
Antigenic drift is the gradual accumulation of mutations.
What is antigenic shift?
Sudden change in antigenic type. When two or more strains of a virus combine to make a totally new type, by using the antigens of the original strains combined.
What types can capsids be?
Simple and complex, helical or icosahedral.
Where does the virus life cycle occur?
Entirely within the host cell.
What can virus characters be described as in terms of time?
Chronic, latent or lytic.
At what stage in its lifecycle is a virus infectious?
As a virion
What are the stages to the virus life cycle?
Entry, Replication, Assembly and Release.
How do retroviruses infected human cells?
make DNA reverse transcript of their RNA genome before doing anything else. This is then integrated into the chromosomal DNA. Infection is therefore irreversible.
What is the difference between naked and enveloped viruses?
Viruses that replicate by bursting cells – lytic infection – tend to be naked particles i.e. capsid with spikes. Viruses that bud chronically from sick cells tend to pick up a membrane as they leave and so are called enveloped.
How does influenza rearrange its genes?
Antigenic drift is the gradual accumulation of mutations which happens in flu due to selective pressure. Over a series of flu seasons the virus gradually changes into a strain able to evade abs originally there, at which point it may reinfect.
Type A flu can use drift and shift which causes most pandemics.
Because of its segmented genome, human influenza also infects birds and pigs. So human, bird or pig flu co-infected the same organism resulting in re-assortment of the individual segments is possible. This is antigenic shift and can lead to a new strain of flu. Happens every 10-30 years.
What are viruses?
Obligate intracellular parasites
What are the immune mechanisms used by the immune system to fight off viruses?
Innate: IFNα, β limit the infections
NK cells identify stress signals and recognise virally infected cells.
Adaptive: CD8 and CD4 recognise and destroy virally infected cells, resolve acute infection, carry out immunosurveillance for latent viral infections. CD4 important for humoral immune responses and Abs for re-infection with viruses.
What are the 3 main parts to a virus?
Nucleic acid surrounded by protein shell - capsid and sometimes in turn surrounded by a membranous envelope.
What are RNA sense and antisense?
RNA sense is same as mRNA so can be immediately translated in the host cell. Anti-sense RNA must first be converted to sense RNA, by RNA polymerase before translation. Some viruses have a bit of both called ambisense.
What are the 3 viral components synthesised in the host cell once it has entered?
Eclipse phase:
1) essential replication factors needed for genome synthesis
2) subunits that are assembled to form new capsids and virions - structural proteins
3) copies of the viral genome, which are packaged into new capsids.
