Viral-cell interactions: cytopathic effects- Sx of infection on cells cytocidal infection- cell dies persistent infection- productive vs nonproductive detection in vitro cell receptors not for virus especially- [See
Cann, Table 4.1] multiple attachments irreversible Effects related to membrane changes: immune response; hemagglutination by viral
hemagglutinin; Permissive or abortive infection: *approaches to treatment must be aware of danger- may
not eliminate, but may just block replication Inclusion bodies: localized changes at sites of viral
replication various names based discoverer- Guarnieri's bodies-
pox; Negri bodies- rabies plants have inclusions too- often true crystals seen,
since cells don't lyse & virus concentration gets
very high mixed inclusions: virus + cellular material other inclusions: little or no virus vacuoles: Eg: SV40 & spumavirus CPE-cytopathic effects: some are dependent on type of cell infected lysis- via viral product or apoptosis Biochemical changes: viral effects may be either direct
or indirect pox & areana- gradual mode of inhibition can vary- thru mRNA competition RNA synthesis- seen in cytocidal viral infections DNA synthesis- generally declines cellular stimulation induction of cell division- Eg: SV40 Viral modification: 2. recombination- exchanged genes during
co-infection 3. transduction- cellular genes incorporated in viral
genome 4. attenuation- decreased virulence due to small
changes utilized in vaccines- Sabin polio, measles
MUCH less is known in eukaryotes compared to
prokaryotes
much more complex & more difficult to study
Receptors & membranes:cell surface characteristics important- site of
viral attachment
glycosylations generally involved
initial contact- one attachment site
reversible
viral protein expression on cell surface during
maturation of some enveloped viruses-> several effects
lectins from plants bind glycosylated proteins;
aggregation;
fusion- 2 types: fusion from within- virus infected,
fusion from without- uninfected cells c external
virus*fusion as tool: allows entry of viruses into
unnatural host
nonpermissive- infection aborts but may be
latent
Viral effects on cell morphology &
biochemistry:light microscope- inclusions visible
location characteristic of particular virus- cytoplasm,
nucleus, at cyto-nuclear interface
Eg: reovirus, arenavirus
Eg: herpes, polio
virus which bud usually don't kill cells
Eg: retrovirus & paramyxovirus
Eg: togavirus lyses animal cells, buds from
insect cells
protein synthesis- timing and extent of
inhibition varies
Eg: picorna- & toga- complete shutdown
Eg: pox & areana
most effects on RNA are on mRNA; some effect
rRNA
Eg: small DNA viruses, as papovaviruses
1. phenotypic mixing- exchanged coats during
co-infection
Eg: rhabdo-, herpes, retro-, paramyxo-
Eg: retro-, influenza
Eg: myxomatosis in Australia
Next week:Tumorigenesis- comparing DNA & RNA tumor
viruses- read Cann, ch 7
Emerging viruses- Cann, ch 7, on-line: CDC
Updated 1/25/04 by thatcher@sonoma.edu