Key ideas

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Key ideas:

origins:

- RNA viruses preceded DNA viruses: RNA has no proofreading more errors (DNA evolved proofreading, less errors)

- high mutations in RNA viruses give rise to quasispecies

antigenic shift:

- slow accumulation of point mutations

antigenic drift:

- dramatic changes (reassortment) of viruses with segmented genomes

quasispecies:

- closely related but non-identical recombinant viral genomes

- help the virus persist in the population

viral dynamics:

- if antigenic diversity is below threshold limit the population is controlled by the immune response

- if diversity exceeds limit the immune response breaks down

pathogenesis of a pathogen:

- a pathogen will

attach to the host

penetrate the host

cause damage

evade the immune response

host cell damage

- many viruses are able to shut down host protein synthesis

immune evasion:

- poxviruses:

interleukin one receptor encoded by virus may bind IL-1B and inactivate the cytokine

block TNF and IFN-y (IFNyR)

-herpesvirus

avoid apoptoses attaching ICP47 to TAP preventing viral peptides loading onto MHC class I

-Epstein Bar

produces BHRF1 similar to cellular protein thats important in apoptosis pathway

oncogenic retroviruses

- transducing:

highly carcinogenic (V oncogenes)

-non-transducing:

not all infected animals develop tumours (C oncogenes)

- long latency

tumours are rare and appear years after infection