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Influenza viruses

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Topic updated on 12/18/16 6:18am

Introduction
  • Classification
    • Virus
      • RNA
        • Negative-stranded
          • Orthomyxovirus
            • Influenza
              • Influenza A
              • Influenza B
  • Pathogenesis
    • transmission
      • respiratory
      • direct contact
      • animal-to-human (strain dependent)
    • reservoir
      • birds (A)
      • pigs (A)
      • humans (A and B)
    • molecular biology
      • glycoproteins
        • hemagglutinin antigen (H)
          • promotes viral entry
        • neuraminidase antigen (N)
          • promotes progeny virion release
      • antigenic drift
        • minor changes in H or N due to random mutation
        • causes epidemics
      • antigenic shift
        • reassortment of viral genome
          • e.g. human flu combining with swine flu
        • causes pandemics
        • only Influenza A can undergo antigenic shift
        • "shift is when shit hits the fan"
Diseases
  • Epidemic influenza
    • small changes in viral genome
    • late December to early March
    • fever, chills, headaches, malaise, myalgia
    • respiratory symptoms
    • risk of bacterial pneumonia/superinfection
    • complications include Reye's syndrome or Guillain-Barré syndrome
  • Pandemic influenza
    • dramatic changes in viral genome lead to high susceptibility of infection worldwide
    • higher risk of bacterial pneumonia/superinfection
      • S. aureus
      • S. pneumoniae
      • H. influenzae
Laboratory
  • Characteristics
    • RNA
      • single-stranded
      • negative sense
      • linear
      • segmented genome
        • 8 segments
    • enveloped
    • helical
  • Diagnosis
    • culture
    • detection of viral proteins
    • detection of viral RNA
    • detection of antibodies
      • anti-hemagglutinin IgG and IgA prevent reinfection
Treatment
  • Vaccine
    • killed
      • reformulated each fall and offered to at risk groups (e.g. elderly, healthcare workers)
      • 2 strains of influenza A + 1 strain of influenza B
      • stimulates generation of host antibodies against hemagglutinin
        • interferes with viral binding and entry into host cells
    • live attenuated
      • intranasal
  • Drugs
    • amantadine/rimantadine
      • inhibits viral uncoating
      • most strains are now resistant
    • oseltamivir/zanamivir
      • neuraminidase inhibitors


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