T2 L10: Respiratory infections

Cards (55)

  • lungs are constantly exposed to particulate material and microbes from the upper airway
  • lower airways are usually devoid of conventional pathogens
  • innate immunity
    cilia - removes debris and pathogens
    alveolar macrophages
  • function of alveolar macrophages:
    secrete antimicrobials
    engulf and kill pathogens
    recruit other immune cells
    process and present antigens to T cells
  • acquired immunity
    B/T cell responses
    IgA secreted by plasma cells - interferes with adherence and viral assembly
  • viral rhinitis (common cold)
    upper respiratory tract infection
    rhinovirus = most common
    coronaviruses - 10-15%
    >200 viral subtypes
  • viral rhinitis transmission
    hand contact
    droplet transmission

    IP 2-3 days, lasts 3-14 days
  • what causes sore throat and blocked nose in colds?
    bradykinin: intranasal administration causes sore throat and nasal congestion due to vasodilation
  • what causes sneezing?
    histamine-mediated - by stimulation of the trigeminal sensory nerves
  • what causes nasal discharge?
    due to myeloperoxidase, changes colour with increasing number of neutrophils
  • what causes you to cough?
    mediated by the vagus nerve - inflammation has to extend to larynx to trigger this
  • what is responsible for systemic symptoms eg. fever?
    cytokines
  • differences between cold and flu:
    flu is basically a more severe and acute cold
  • uncomplicated influenza
    most caused by influenza A/B virus
    IP 1-4 days lasts 3-7
    abrupt onset of symptoms - fever + cough / sore throat
    acutely debilitating
    fever 38-41 c
  • influenza risk groups for complications:
    immunosuppressed/ chronic conditions
    pregnancy/2 weeks postpartum
    <2yrs/>65yrs
    BMI>40
  • complications associated with influenza:
    primary viral pneumonia
    secondary bacterial pneumonia
    CNS disease
    death
  • recap: stages of viral pathogenesis
    Attachment
    penetration
    synthesis of new components
    assembly
    release
  • how does influenza enter the cell?
    influenza virus haemagglutinin surface protein (H) binds sialic acids on cell surface glycoproteins and glycolopids in the respiratory tract, allowing it to enter the cell.
  • how does the influenza virus prevent escaping virions from clumping together?
    neuraminidase (N) on surface of virus allows it to escape by cleaving sialic acid bonds
  • influenza virus has a segmented genome (8 parts) so can reassort if two different viruses infect the same cell
  • influenza shift and drift: antigenic drift
    neutralising antibodies against haemagglutinin block binding to cells
    mutations alter haemagglutinin epitopes so that the neutralising antibody no longer binds
  • multiple reassortment events in virus genome can cause it to infect other animals eg. humans
  • treatment and prevention of influenza
    active immunisation against haemagglutinin and neuraminidase
    hand hygiene and droplet precautions
  • Epiglottis/ HiB
    Haemophilus influenzae b infection
    disease of adults
    symptoms include:
    drooling, dysphagia, distress
    risk of sudden complete airway obstruction
    ENT emergency
  • croup/ laryngotracheobronchitis
    inflammation of the larynx, trachea and bronchi
    = upper airway obstruction, especially at the narrowed subglottic region
    parainfluenza virus most common
  • croup symptoms
    barking cough, inspiratory stridor, hoarse voice
    hypoxia is a late sign and very worrying
    use of accessory muscles
  • croup management
    reduce inflammation (steroids +- adrenaline)
  • acute bronchitis
    lower respiratory tract infection
    damage to bronchial walls -> increased mucus production + oedema of bronchus = productive cough
  • acute bronchitis symptoms
    usually viral
    assoc. with URTI symptoms
    may be wheeze/ dyspnoea
    no fever/ systemic upset
    cough continues after infection cleared as bronchial wall has to heal - may take weeks
  • bronchiolitis
    acute infection of the epithelial cells lining the small airways
    results in oedema, increased mucus production, cell death
    the debris and oedema obstructs the distal airways
    disproportionate narrowing in expiration means air trapping and wheeze
  • what is the cause of bronchiolitis?
    majority caused by RSV (respiratory syncitial virus)
    usually children <2yrs
  • bronchiolitis symptoms
    cough wheeze and tachypnoea
    increased work of breathing
    fever; corzya
  • bronchiolitis diagnosis and treatment
    viral nose/throat swab or respiratory secretions for RT-PCR
    treatment = supportive care
  • pneumonia - pathophysiology
    pneumonia = infection of the lung parenchyma
    alveoli full of inflammation = blocks oxygen transfer
  • pneumonia symptoms
    fever, breathlessness, cough, sputum production
    hypoxia, increased respiratory rate
    pleuritic chest pain
    sepsis
  • radiology - diagnosis of pneumonia
    requires infiltrates on a plain CXR with supporting clinical features
    consolidation: alveoli and bronchioles completely filled with inflammatory debris/pus/pathogens
    heart borders or diaphragm obscured due to the loss of solid-gas interface
    air bronchograms- air in larger bronchi outlined by surrounding consolidation
  • classifications- most useful:
    community vs hospital-acquired - useful as pathogens involved differ in their % contribution
  • community-acquired pneumonia pathogens
    Streptococcus pneumoniae
    Haemophilus influenzae
    Mycoplasma pneumoniae
    Legionella pneumophila
    Staphylococcus aureus
  • streptococcus pneumoniae
    commonest organism - gram positive diplococci, acquired in nasopharynx
    asymptomatic carriage in 40-50% ppl
  • risk factors for strep. pneumoniae
    alcohol dependency, respiratory disease, smokers, hyposplenism, chronic heart disease
    HIV - 50 o 100 fold increase in invasive pneumococcal disease