Viral infections, oncoviruses & antiviral chemotherapy Flashcards
Dynamics of viral infections
To cause diseases:
Infect their specific host’s cells
replicate efficiently within the host
damage targeted tissues
Viral pathogenesis: the process of a virus producing a disease
3 requirments;
Enough virus
Accessible Cells that permits the viral replication
Local antiviral defense/immune system absent or overcome
Acute viral infections
(short-term)
Asimptomatic infection
Acute infection
Asymptomatic infection
what are the signs and symptoms?
Most virus encounters have no consequence
Many infections are inapparent or asymptomatic
Signs: Evidence of disease that can be observed by others
Symptoms: Apparent only to the patient
Acute infection
Viruses can cause acute infections
display short incubation periods upon virus entry into the host.
Rapid onset of disease
Brief period of sympthoms
Quick resolution (elimination of virus by the immune system)
The range of clinical manifestations. Factors?
Genetic factors
Age
Comorbidity (other diseases)
Individual immune response
Latent or persistent viral infections
Latent infection
Persistent/Chronic infection
Latent infection
Latent virus remains in asymptomatic host cell for long periods
No symptoms or viruses are detectable/active
May reactivate due to changes in immunity
Cold sores (e.g. herpes simplex virus, HSV-1), shingles (varicella zoster virus, VZV)
Persistent/Chronic infection
A persistent viral infection occurs gradually over a long period;
Hepatitis B virus (HBV )infection, where the virus continue to replicate over time a low level
Not all HBV infections become chronic
Herpesvirus – latency
Herpes simplex viruses (HSVs) and varicella-zoster virus (VZV) remain latent in a quiescent but persistent form (latent infection), in neural ganglia cells
Primary infection occurs producing:
- cold sore usually for HSV-1
- Chicken pox for VZV
Infections produces progeny virions that spread elsewhere
Virus enters innervating sensory neurons, and viruses are transported to the neuronal cell body
Where is viral DNA released?
released into the neuronal nucleus and
circularizes (episomal state)
Circular viral DNA persists in the neuronal cell nucleus
Herpesvirus – reactivation
HSV-1
Varicella Zooster Virus
HSV-1
HSV-1 can periodically reactivate to cause cold sores, in response exposure to sunlight, psychological stress, fever, menstruation and surgical resection
Reactivation in the neuronal cell body
Newly formed capsids are transported to the axonal termini
Infectious virus is released from the axon and infects epithelial cells, resulting in recurrent infection and virus shedding
Varicella Zooster Virus
VZV after years of inactivity, may produce the skin disease shingles (herpes zoster)
localised painful and maculopapular rash
in one or two adjacent dermatomes - on trunk