Dissemination, Virulence and Epidemiology Chapter 14

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Dissemination, Virulence and Epidemiology-
Chapter 14

• Purpose To understand how viruses cause disease

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Viral pathogenesis

• Virulence
• Mouse as model

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Requirements

• Sufficient virus must be available
• The cells at the site of infection must be
  accessible, susceptible and permissive
• Local host antiviral defense system must be
  absent or initially ineffective

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Sites of viral entry
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Routes
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Respiratory Tract
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Intestinal entry
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Skin
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Kinetics
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Blood-borne viruses
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Mousepox
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Spread of infection
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Alphaherpesvirus spread
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Spread

• Site of entry often established pathway of spread
• Shedding

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Routes of shedding

• Primary site
• Disseminated
• Respiratory secretions
• Saliva
• Feces
• Blood
• Urine, Semen, Milk
• skin

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Virulence

• Capacity of infection to cause disease
• LD50, PD50, ID50, death in 50 of infected
  animals
• Death or appearance of symptoms
• Measurement of fever or weight loss

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Viral virulence genes

• Affect the ability of virus to replicate
• Modify the hosts defense mechanisms
• Facilitate virus spread in and among hosts
• Directly toxic

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Epidemiology-pop disease
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Transmission

• Perpetuation of infection in one species
• Alternate infection of insects and vertebrate
  hosts

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Seasonal variations
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Susceptibility

• Immunity
• Genetic
• Age
• Male/female
• Malnutrition