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L14 - Patterns of Viral Infections
Understand the basis of how viruses…
L14 - Patterns of Viral Infections
- Understand the basis of how viruses cause disease
- Understand how virus enter the host, the important target organs, and the subsequent diseases which viruses cause
- Understand the concept of viral infectiousness and how it is measured
- Understand the general patterns of viral infection
- Understand how the major diseases used as examples here, establish acute or persistent infection
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Important Target Organs
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PULMONARY/LUNGS
- Respiratory infection either Localised (primary infection) or Symptomatic/Secondary to global infection
Hepatic/Liver
- Caused as primary infection (hepatitis virus)
- Secondary infection to global illness
Renal/Kidney
- Rarely infected - CMV infects proximal renal tubes
Central Nervous System
Seldom primary infection, typically infected during VIREMIA => haematogenous spread
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Virulence
A comparison of the severity of disease caused by antigenically variant viruses within the same quasispecies
=> Tendency to mutate enhances these virulence factors;
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Ability to disseminate
Haematogenous Spread
Viremia = viral concentration in blood
Passive V. = introduction to blood
Primary V. = inf. tissue + replication
Secondary V = haematogenous spread
- Direct entry to blood via intra-veinous inoculation = bite => haematogenous dissemination
- Infection of endothelial cells => viral replication extrudes into blood stream => haematogenous dissemination
- Virus contaminate extracellular (interstitual) fluid => drain to drain lymph node => haematogenous spread
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Transmission
Infectiousness of a virus quantified by the
Reproduction Number (Ro)
=> Av number of secondary cases generated by one primary case
Hep C = 2
HIV = 4
Measles = 18
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