Prevention and Control of Viral Diseases Chapter 19

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Prevention and Control of Viral DiseasesChapter
19

• Purpose To understand how to develop products to
  control viral disease

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Two methods

• Prevention of viral infections by vaccines
• Treatment of viral diseases with drugs

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Caveats

• Any agent or process that blocks viral
  replication or reduces pathogenesis
• Imposes selection for viral mutants
• Select mutants may be able to bypass blocking
  agent
• As infection is intracellular, any intervention
  affecting host enzyme or process will carry
  inherent risksb

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An example of success smallpox vaccine

• Result of smallpox disease
• death, disfigurement (crippling)
• 1/10 of humankind affected
• Chinese and Indian physicians 1st performed
  variolation in 11th century
• Jenner 1796

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Problems with current smallpox

• Stockpile of Dryvax
• Passaged vaccinia
• Side effects
• AIDS, immunosuppressive drugs
• 2002 military, health care workers

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Large scale vaccination
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Requirements for eradication

• Viral infectious cycle must take place in one
  host
• Infection (or vaccination) must induce lifelong
  immunity

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Smallpox characteristics
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Control of spread

• Identify and stop the spread from niche outbreaks
• ring-slaughter program slaughter every host
  animal in farms at increasing distances
  surrounding an outbreak site
• Sometime may need to all animals on at-risk
  farms

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New vaccines

• Challenge cannot predict the efficacy or side
  effects of vaccines
• Lack knowledge of immune protection against most
  viral infections
• CTL?
• Antibody?

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Vaccine basics

• Vaccines stimulate immune memory
• Presence of T and B lymphocytes that are
  pathogen-specific after infection or vaccination
• Vaccines must establish memory and immunity
  without the pathogenic events
• Immunization processes
• Active
• Passive products of the immune response
• Safe, efficacious and practical
• Herd-immunity- decrease threshold
• 80-95 population having immunity

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Effective vaccines
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Problems with weak immunity

• Protection against subsequent infection may be
  inadequate
• Viral replication may occur in the presence of
  weak immune effectors
• Mutants that can escape the hosts immune
  response may be selected and transmitted to
  population

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Different types of vaccines
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Live attenuated

• Passage in cell lines
• Temperature mutants

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Sabin vaccine
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Measles vaccine
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Recombinant DNA technology
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Inactivated or killed virus vaccines

• Treatment with formalin or extraction of
  enveloped virus particles with nonionic
  detergents
• Accidents Salk polio vaccine
• Flu vaccine

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Subunit vaccines

• Purified components of viruses
• Recombinant DNA technology- beneficial because
  can produce only proteins of interest

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Adjuvants
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Delivery vehicles
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Available vaccines
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New vaccinia virus vectors
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Epitope screening
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DNA vaccines
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DNA vaccines results
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Immunotherapy candidates