virology 3 Flashcards
Attachment
virus recognition of the target cell
binding virus attachment proteins (VAPs) on the surface of virion on the receptors on the target cell
Non-enveloped VAPs
part of the capsid or a protein extending from the capsid
Enveloped VAPs
spike/peplomer glycoprotein on the envelope
Receptor
protein, carbohydrates on glycoproteins or glycolipids on the cell surface
receptors on the host cell determine host range, tissue tropism
Penetration
3 types
entry into the cell
energy dependent, rapid
fusion
envelope
fuse with cell membrane
endocytosis
enveloped
translocation
non-enveloped virions
bind attach and simple pass through
uncoating
protective protein shell
nucleocapsid is disintegrated
genome freed in cytoplasm
protein disintegrate in cytoplasm
following uncoating synthesis of viral proteins by cellular metabolism
translation
viral RNA/protein utilize cellular machinery
viral mRNA translation to viral protein is essentially the same as cellular mRNA
posttranslational modifications
macromolecular synthesis
transcription, translation, posttranslational modification and viral genome replication
DNA viruses
replication in nucleus
most use host cell’s DNA-dependent RNA polymerase II and other enzymes to transcribe viral mRNA
RNA virus
replicate in cytoplasm: must encode or carry necessary enzymes for transcription and replication in their genomes
assembly
viral matrix protein brings viral nucleocapsid to the cell membrane
maturation
budding virion
no cellular protein on the membrane
all viral protein
Release
take portion of cell membrane
completely replace cell protein with viral protein
free infectious virion
Steps:
attachment
penetration
uncoating
macromolecular synthesis
transcription and translation
replication
assembly (maturation)
release
Cytopathic Effect (CPE)
morphological changes of infected cells such as rounding, lysis, detachment, syncytia, inclusion bodies
causes of CPE formation
direct pathological injury of the infected cells
side effect (altered metabolism due to virus replication)
site of replication
dna virus in nucleus
rna virus in cytoplasm
effect of viruses on cell metabolism
inhibit everything because they need those machinery to translate viral protein
Entry of virus into the host
respiratory tract
GI tract
conjunctiva
genitourinary tract
skin
skin
natural barrier-outer layer contains keratinized dead cells of stratum corneum
respiratory tract
barriers
mucus, mucociliary movement, neutrophils, macrophages
IgA, CMI
droplet size, air current, humidity, temperature
Gastrointestinal tract
barriers
low pH
proteases
bile salts
mucus
IgA, CMI
enzymatic enhancement
Genitourinary tract
barriers: mucus, IgA, CMI
Conjunctiva
Barriers: tear, IgA and IgG
Hematogenous spread-Viremia
vascular system: major pathway, systemic spread
entry site:limited replication
primary viremia-spread to distant organs (major replication site)
secondary viremia: major clinical signs
high viremia=virulence
lymphatic spread
lymphatic spread-less important than viremia
primary replication-epithelial cells, vascular system
spread-lymphatic vessels to other tissues
neural spread
factor influencing the spread via CNS
primary replication site
viremia (titer and length)
duration of nerve tissue exposure
transport speed: 2-16 mm/day along nerve axon
