viruses and what they do - an overview wednesday, august 25, 2010
TRANSCRIPT
Viruses and what they do -
An overview
Wednesday, August 25, 2010
Viruses (Encyclopedia Britannica)
..infectious agents of small size and simple composition that can multiply only in living cells of animals, plants and bacteria. Viruses are obligate parasites that are metabolically inert when they are outside their hosts. They all rely, to varying extents, on the metabolic processes of their hosts to reproduce themselves. The viral diseases we see are due to the effects of this interaction between the virus and its host cell (and/or the host’s response to this interaction).
Viral Genomes
Nucleic Acid
DNA
RNA
Double Stranded
Positive
Negative
RNA DNA
Single Stranded
Double Stranded
Single Stranded
SS RNA genomes
Positive(sense)
Negative(anti-sense)
AUG GCA CGA
UAC CGU GCU
met ala arg
• +ve (sense) and -ve (anti-sense) RNA genomes
Virion
capsomeres
Capsid
envelopedVirus or Virion
envelope
capsid
“naked” virus particle or Virion
herpesadeno
Proteins produced by viruses
• Structural proteins• Non-structural proteins
Some viral shapes
adenovirus
parvovirus
papillomavirus
100 nm1 nm = 1 millionth of a mm100 nm = 1 ten thousandth of a mm
“naked” viruses
Some viral shapes
herpesvirus
parainfluenzavirus
influenzavirus
poxvirus
1 nm = 1 millionth of a mm100 nm = 1 ten thousandth of a mm
100 nm
Enveloped viruses
Taxonomy
• What is it?• On what is it based?• Is it important?• Do I need to remember all the details?
International Committee onTaxonomy of Viruses
Viruses with ss DNA genomes
Circoviridae
Parvoviridae
porcine circovirus
canine parvovirus-2
feline panleukopenia virus
porcine parvovirus (SMEDI)
Viruses with ds DNA genomes
Poxviridae
African swine fever virus
Herpesviridae
Adenoviridae
Papovaviridaepapillomaviruses
adenoviruses
bovine herpesvirus-1,2
porcine cytomegalovirus
equine herpesviruses -1,4
african swine fever virus
poxviruses
malignant catarrhal fever virus
Viruses with ds RNA genomes
Reoviridae
Birnaviridae
rotaviruses
bluetongue virus
african horse sickness
infectious bursal disease (chickens)
infectious pancreatic necrosis (salmonid fish)
Viruses with +ve RNA genomes
PicornaviridaeCaliciviridae
Coronaviridae
ArteriviridaeFlaviviridae
Togaviridae
foot and mouth disease virus
porcine enteroviruses
feline calicivirus
equine arterivirus, PRRS
pestiviruses (BVD)
coronaviruses
equine encephalitis viruses
flaviviruses (WNV)
Viruses with -ve RNA genomes
Paramyxoviridae
Rhabdoviridae
Orthomyxoviridae
Filoviridae
Bunyaviridae
parainfluenza viruscanine distemper virus
respiratory syncytial virus
rabies virus
vesicular stomatitis virus
influenzaviruses
Ebola virus
Haantan virus
Hendra, Nipah viruses
Viruses with reverse transcriptase
Retroviridae
Hepadnaviridae
feline leukemia virus
feline, bovine immunodeficiency
viruses
bovine, avian leukosis viruses
caprine arthritis-encephalitis virus
How new serotypes arise – gradual changes in external proteins due to pressure by neutralizing antibodies
Antigenic classification:Serotypes and Groups
antibodies to all viral proteins
selective pressureonexternal viral proteins
antibodies to external proteins neutralize virus
no selective pressure on internal proteins
antibodies to all viral proteins
selective pressureonexternal viral proteins
antibodies to external proteins neutralize virus
selective pressure forces selection of virions with slightly different external proteins
antibodies to all viral proteins
selective pressureonexternal viral proteins
antibodies to external proteins neutralize virus
selective pressure forces slight change in external proteins
virus, including changed virus passed on to new host
process repeated, over time…..
serum from original cat
neutralizesneutralizes neutralizes neutralizes
does not neutralize
NOTE: Only external proteins change. Internal proteins do not change
process repeated, over time
serum from original cat
neutralizesneutralizes neutralizes neutralizes
does not neutralize
new serotype
NOTE: Only external proteins change. Internal proteins do not change
same serotype
Serotype - all isolates of a virus that can be neutralized by a
common antiserum are said to belong to the same serotype.
…..because of changes in external protein (internal proteins do not change)
external proteins are called TYPE SPECIFIC antigensinternal proteins are called GROUP SPECIFIC antigens
process repeated, over time
new serotypesame serotype
different serotypes
same group
Groups, types (sero-types), isolates and ‘strains’
Group
Type -A
Type - B
Type - C
Group specific antigen
Type -A specificantigen
Type - C specificantigen
isolate
Group and type specific antigens
group specific antigen
type specific antigen
“naked”virus(eg FMDV)
enveloped virus(eg influenza, FeLV)
Serotypes and neutralizing antibody (eg. FMDV)
serotypes of FMD virus
A OC SAT1 SAT2 SAT3 Asia
antibodies against receptor binding protein of serotype A will neutralize viruses of serotype A but not of serotype C
receptor
receptor binding protein on viral surface
example - influenza
group specific antigen
type specific antigen
serotype H1 serotype H5 serotype H7
test based on group specific antigen will detect all three
vaccination against one serotype will not protect against others
Infection of a cell
Stage Biological implications
Host defenses
Drug intervention
Distribution of the CCR532 mutation in human populations
from PLoS Biology, Nov 2005
Errors in replication lead to “quasispecies”
persistentinfection
mixture of variant viruses(quasispecies)
inclusion bodies
Release of virus
Release by lysis of cell(cytopathic)
or by budding (withoutdeath of cell, non-cytopathic)