USMLE

Orthomyxovirus

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Viruses - RNA Viruses
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Fact List

  • Orthomyxoviruses
    • Characteristics
      • RNA viruses
        • replicate in the nucleus of cells
          • Unlike most RNA viruses which replicate in cytoplasm of cells
        • Single-stranded
      • - sense
      • Linear chromosome
      • 8 segments
        • Capable of antigenic shift
          • Reassortment of entire genome segments as opposed to single point mutations lead to dramatic shifts in phenotype, causing pandemics
      • Enveloped
      • Helical capsid
    • Key Viruses
      • Influenza virus (flu)
        • Contains antigens
          • hemagglutinin (H)
            • Binds sialic acid receptors on host cell to promotes viral entry
          • neuraminidase (N)
            • Promotes progeny virion release
    • Presentation
      • Fever, cough, sore throat, myalgias
      • Patients at risk for fatal bacterial superinfection
        • Esp. S. aureus, S. pneumo, and H. influenzae
    • Treatment
      • Supportive; pharmacological therapy depends on course and severity
        • Oseltamivir (Tamiflu), zanamivir
          • neuraminidase inhibitor, prevents progeny release
          • Can also reduce viral penetration of mucous secretions on respiratory surface
          • Can shorten course of infection if taken within 48 hours of onset of symptoms
        • Amantadine 
          • Impairs uncoating of influenza A
          • Limited use due to widespread viral resistance
          • Used in other contexts (e.g. Parkinson’s disease) due to modulatory effects on dopamine
    • Vaccination
      • Achieved by antibodies against hemagglutinin (not neuraminidase)
        • anti-H antibodies prevent infection, while anti-N antibodies can only decrease viral shedding and invasion
        • contains viral strains most likely to appear during flu season, due to virus’ rapid genetic changes
      • Killed viral vaccine (intramuscular)
        • Also known as the “flu shot”; most frequently used
      • Live attenuated vaccine (intranasal spray)
        • contains temperature sensitive mutant that replicates in nose but not in lung