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Respiratory Infections

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Organisation (fibrous scarring) Abscess. Bronchiectasis. Empyema (pus in the pleural cavity) Pneumonia fibrous organisation. Bronchopneumonia ... – PowerPoint PPT presentation

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Title: Respiratory Infections


1
Respiratory Infections
2
Respiratory tract defences
  • Ventilatory flow
  • Cough
  • Mucociliary clearance mechanisms
  • Mucosal immune system

3
Upper respiratory tract infections
  • Rhinitis
  • Rhinovirus, coronavirus, influenza/parainfluenza
  • Non-infective (allergic) rhinitis has similar
    symptoms (related to asthma)
  • Sinusitis
  • Otitis media
  • Latter 2 have a risk of bacterial superinfection,
    mastoiditis, meningitis, brain abscess

4
Laryngitis
  • Most commonly upper respiratory viruses
  • Diphtheria
  • C. diphtheriae produces a cytotoxic exotoxin
    causing tissue necrosis at site of infection with
    associated acute inflammation. Membrane may
    narrow airway and/or slough off (asphyxiation)

5
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6
Acute epiglottitis
  • H. influenza type B
  • Another cause of acute severe airway compromise
    in childhood

7
Pneumonia
  • Infection of pulmonary parenchyma with
    consolidation

8
Pneumonia
  • Gr. disease of the lungs
  • Infection involving the distal airspaces usually
    with inflammatory exudation (localised oedema).
  • Fluid filled spaces lead to consolidation

9
Classification of Pneumonia
  • By clinical setting (e.g. community acquired
    pneumonia)
  • By organism (mycoplasma, pneumococcal etc)
  • By morphology (lobar pneumonia, bronchopneumonia)

10
Pathological description of pneumonia
11
Organisms
  • Viruses influenza, parainfluenza, measles,
    varicella-zoster, respiratory syncytial virus
    (RSV). Common, often self limiting but can be
    complicated
  • Bacteria
  • Chlamydia, mycoplasma
  • Fungi

12
Lobar Pneumonia
  • Confluent consolidation involving a complete lung
    lobe
  • Most often due to Streptococcus pneumoniae
    (pneumococcus)
  • Can be seen with other organisms (Klebsiella,
    Legionella)

13
Clinical Setting
  • Usually community acquired
  • Classically in otherwise healthy young adults

14
Pathology
  • A classical acute inflammatory response
  • Exudation of fibrin-rich fluid
  • Neutrophil infiltration
  • Macrophage infiltration
  • Resolution
  • Immune system plays a part antibodies lead to
    opsonisation, phagocytosis of bacteria

15
Macroscopic pathology
  • Heavy lung
  • Congestion
  • Red hepatisation
  • Grey hepatisation
  • Resolution
  • The classical pathway

16
Lobar pneumonia (upper lobe grey hepatisation),
terminal meningitis
17
Pneumonia fibrinopurulent exudate in alveoli
(grossly red hepatisation)
18
Pneumonia neutrophil and macrophage exudate
(grossly grey hepatisation)
19
Complications
  • Organisation (fibrous scarring)
  • Abscess
  • Bronchiectasis
  • Empyema (pus in the pleural cavity)

20
Pneumonia fibrous organisation
21
Bronchopneumonia
  • Infection starting in airways and spreading to
    adjacent alveolar lung
  • Most often seen in the context of pre-existing
    disease

22
Bronchopneumonia
23
Bronchopneumonia
  • The consolidation is patchy and not confined by
    lobar architecture

24
Clinical Context
  • Complication of viral infection (influenza)
  • Aspiration of gastric contents
  • Cardiac failure
  • COPD

25
Organisms
  • More varied Strep. Pneumoniae, Haemophilus
    influenza, Staphylococcus, anaerobes, coliforms
  • Clinical context may help. Staph/anaerobes/colifor
    ms seen in aspiration

26
Complications
  • Organisation
  • Abscess
  • Bronchiectasis
  • Empyema

27
Viral pneumonia
  • Gives a pattern of acute injury similar to adult
    respiratory distress syndrome (ARDS)
  • Acute inflammatory infiltration less obvious
  • Viral inclusions sometimes seen in epithelial
    cells

28
The immunocompromised host
  • Virulent infection with common organism (e.g. TB)
    the African pattern
  • Infection with opportunistic pathogen
  • virus (cytomegalovirus - CMV)
  • bacteria (Mycobacterium avium intracellulare)
  • fungi (aspergillus, candida, pneumocystis)
  • protozoa (cryptosporidia, toxoplasma)

29
Diagnosis
  • High index of suspicion
  • Teamwork (physician, microbiologist, pathologist)
  • Broncho-alveolar lavage
  • Biopsy (with lots of special stains!)

30
Immunosuppressed patient fatal haemorrhage into
Aspergillus-containing cavity
31
HIV-positive patient CMV (cytomegalovirus) and
pulmonary oedema on transbronchial biopsy.
32
Special stain also shows Pneumocystis
33
Tuberculosis
  • 22 million active cases in the world
  • 1.7 million deaths each year (most common fatal
    organism)
  • Incidence has increased with HIV pandemic

34
Tuberculosis
  • Mycobacterial infection
  • Chronic infection described in many body sites
    lung, gut, kidneys, lymph nodes, skin.
  • Pathology characterised by delayed (type IV)
    hypersensitivity (granulomas with necrosis)

35
Tuberculosis (pathogenesis of clinical disease)
  1. Virulence of organisms
  2. Hypersensitivity vs. immunity
  3. Tissue destruction and necrosis

36
Mycobacterial virulence
  • Related to ability to resist phagocytosis.
  • Surface LAM antigen stimulates host tumour
    necrosis factor (TNF) a production (fever,
    constitutional symptoms)

37
Organisms
  • M. tuberculosis/M.bovis main pathogens in man
  • Others cause atypical infection especially in
    immunocompromised host. Pathogenicity due to
    ability
  • to avoid phagocytosis
  • to stimulate a host T-cell response

38
Immunity and Hypersensitivity
  • T-cell response to organism enhances macrophage
    ability to kill mycobacteria
  • this ability constitutes immunity
  • T-cell response causes granulomatous
    inflammation, tissue necrosis and scarring
  • this is hypersensitivity (type IV)
  • Commonly both processes occur together

39
Pathology of Tuberculosis (1)
  • Primary TB (1st exposure)
  • inhaled organism phagocytosed and carried to
    hilar lymph nodes. Immune activation (few weeks)
    leads to a granulomatous response in nodes (and
    also in lung) usually with killing of organism.
  • in a few cases infection is overwhelming and
    spreads

40
Pathology of Tuberculosis (2)
  • Secondary TB
  • reinfection or reactivation of disease in a
    person with some immunity
  • disease tends initially to remain localised,
    often in apices of lung.
  • can progress to spread by airways and/or
    bloodstream

41
Tissue changes in TB
  • Primary
  • Small focus (Ghon focus) in periphery of mid zone
    of lung
  • Large hilar nodes (granulomatous)
  • Secondary
  • Fibrosing and cavitating apical lesion (cancer an
    important differential diagnosis

42
Primary and secondary TB
  • In primary the site of infection shows
    non-specific inflammation with developing
    granulomas in nodes
  • In secondary there are primed T cells which
    stimulate a localised granulomatous response

43
Primary TB Ghon Focus
44
Secondary TB
  • Necrosis
  • Fibrosis
  • Cavitation
  • T cell response CD4 (helper) enhance killing.
    CD8 (cytotoxic) kill infected cells giving
    necrosis

45
Granulomatous inflammation with caseous necrosis
46
Acid fast stain spot the organism (a red
snapper)!
47
Complications
  • Local spread (pleura, lung)
  • Blood spread. Miliary TB or end-organ disease
    (kidney, adrenal etc.)
  • Swallowed - intestines

48
The host-organism balance
  • Not all infected get clinical disease
  • Organisms frequently persist following resolution
    of clinical disease
  • Any diminished host resistance can reactivate
    (thus 33 of HIV positive are co-infected with TB

49
Secondary TB rapid death due to miliary disease
50
Miliary white foci blood spread to lower lobe
51
Galloping consumption TB bronchopneumonia
52
Decreased immunity many more organisms on acid
fast stain
53
Why does disease reactivate?
  • Decreased T-cell function
  • age
  • coincident disease (HIV)
  • immunosuppressive therapy (steroids, cancer
    chemotherapy)
  • Reinfection at high dose or with more virulent
    organism

54
Lung Abscess
  • Localised collection of pus. Central tissue
    destruction. Lined by granulation tissue/fibrosis
    (attempted healing)
  • Tumour-like
  • Chronic malaise and fever

55
Lung abscess
  • Organisms
  • Staphylococcus
  • Anaerobes
  • Gram negatives
  • Clinical contexts
  • Aspiration
  • Following pneumonia
  • Fungal infection
  • Bronchiectasis
  • Embolic

56
Bronchiectasis
  • Abnormal fixed dilatation of the bronchi
  • Usually due to fibrous scarring following
    infection (pneumonia, tuberculosis, cystic
    fibrosis)
  • Also seen with chronic obstruction (tumour)
  • Dilated airways accumulate purulent secretions

57
Bronchiectasis (2)
  • Affects lower lobes preferentially
  • Chronic recurring infection sometimes leads to
    finger clubbing

58
Complications of bronchiectasis
  • Pneumonia
  • Abscess
  • Septicaemia
  • Empyema
  • Metastatic abscess
  • Amyloidosis

59
Bronchiectasis with chronic suppuration
60
Bronchiectasis
61
Bronchiectasis distal to an obstructing tumour
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