Orthomyxovirus

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Viruses - RNA Viruses

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