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Micro - Intro to Viruses (ii) (Viral rep (attachment + entry (adsorption,…
Micro - Intro to Viruses (ii)
Viral rep
attachment + entry
adsorption, penetration, envelope fusion with membrane
internalised via endocytsosis
uncoating
makes genome available
migration of genome to nucleus
transcription
replication of genome (in nucleus or cytoplasm - many strategies)
translation (protein synthesis always in cytoplasm)
assembly + release of new viruses
if naked released via lysis/exocytosis - results in host cell death
if enveloped: budding
viral pathogenesis
interactions with target tissue
viraemia
cytopathological activity
death
transformation (immortalised)
premalignant/malignant cells (e.g. HPV)
latent infection (with potential to reactivate - e.g. herpes)
Oncogenic viruses
hep B+C (hepatocellular cancer)
HPV (cervical cancer)
HIV + EBV (lymphoma)
EBV (NP carcinoma)
HIV with HH8 (kaposi's sarcoma)
Human T-lymphotropic virus 1 (HTLV1) - T cell leukaemia
Viral spread
intracellular
cell-cell via intercellular bridges (e.g. HSV)
extracellular
locally/distally
haematogenously/via lymphatic system
e.g. influenza
neural
from peripheral Ns to CNS (e.g. rabies, HSV)
nuclear
viral genome incorporated into host genome + passed onto next generation
e.g. HIV
Outcomes of viral infection
can be acute/chronic
most are mild + self-limiting (increase fluid intake + take paracetamol for pyrexia)
can be severe in vulnerable patients
can be silent (e.g. Hep)
can recur intermittently (e.g. HSV)
can be fatal (e.g. rabies)
antiviral agent classes
direct deactivation (UV, cryotherapy)
inhibit viral rep (acyclovir)
alter host response (IFN)
Prevention through vaccines
herd immunity
influenza, MMR, hepA+B, polio, HPV
Lab Dx
detection + ID
microscopy
EM: fast + specialised
fluorescent: rapid, uses commercial fluorescently-labelled Igs to detect viral antigens
light: search for inclusion bodies (virus-induced masses in cytoplasm of cells - e.g. Negri bodies in hippocampus in rabies)
culture
living suspected virally-infected cells needed
examined for effects of viral growth
cytopathic effect (structural changes)
destruction
degeneration
swelling
clumping
inclusion bodies
haemabsorption (stick to RBCs)
ID then must be confirmed by immunofluorescence/ neutralisation/ haemabsorption inhibition
disadvantages
takes long (up to 4 wks)
often poor sensitivity (depends on specimen condition)
susceptible to bacterial contamination/toxins
many won't grow in culture (Hep,HPV,parvovirus,diarrhoeal viruses)
serology
Ig detection
2 samples, 1 @ onset + 1 7-14 days later - look for increase
e.g. ELISA for HIV Ig (colour change)
antigen detection
e.g. Hep B surface antigen (HBSAg)
genome detection (molecular tests)
rapid
guides Tx (e.g. HIV viral load)
detects resistance
measure amount (viral load)