Infections of the Respiratory tract

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Infections of the Respiratory tract

• Most common entry point for infections
• Upper tract
• nose, nasal cavity, sinuses, mouth, throat
• Lower tract
• Trachea, bronchi, bronchioles, and alveoli in the
  lungs

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Fig. 21.1a
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Protective Mechanisms

• Normal flora Commensal organisms
• Limited to the upper tract
• Mostly Gram positive or anaeorbic
• Microbial antagonist (competition)

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Protective Mechanisms
Clearance of particles and organisms from the
respiratory tract
Cilia and microvilli move particles up to the
throat ? where they are swallowed. Alveolar
macrophages migrate and engulf particles and
bacteria in the alveoli.
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Other Protective Mechanisms

• Nasal hair, nasal turbinates
• Mucus
• Involuntary responses (coughing, etc.)
• Immune cells
• sIgA

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Upper respiratory tract

• Rhinitis Common cold
• Common Cold virus over 100 serotypes
• Sinusitis
• Miscellaneous comensual bacteria
• Pharyngitis
• Group A Strep - Streptoccus pyogenes
• Many viruses
• Diphtheria - Corynebacterium diphtheriae

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Pharyngitis

• Group A Strep
• Primary Pharyngitis
• ?
• Secondarily
• Scarlet fever erythrogenic toxin
• Rheumatic fever Heart damage
• Glomerulonephritis Kidney damage

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Upper and lower respiratory tract

• Whooping cough Bordetella pertusis
• Respiratory syncytial virus (RSV)
• Influenza virus

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• Influenza Virus
• New human strains every year
• Mutations
• Pandemic strains ?
• Genetic Recombinant Viruses 1957 Asian Flu
  H2N2
• 1968 Hong Kong Flu H3N2
• 1977 Russian Flu H1N1
• Bird Flu
• Directly from birds
• ?? H5N1

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H and N Flu Glycoproteins

• H Hemagglutinin ?
• Specific residues bind to host cells of
• the respiratory mucosa
• Different residues are recognized by
• the host antibodies
• Residues are subject to changes

• N - Neuraminidase
• Breaks down protective
• mucous coating
• Assist in viral release

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Lower respiratory tract

• Tuberculosis
• Pneumonia
• Viral, bacterial
• And fungal agents

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Tuberculosis

• Bacterial infection
• Mycobacterium tuberculosis

A tubercle in the lung is a granuloma consisting
of a central core of TB bacteria inside an
enlarged macrophage, and an outer wall of
fibroblasts, lymphocytes, and neutrophils.
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Tuberculosis

• Primary
• Lung tubercles, caseous, tuberculin skin reaction
• Secondary (reactivation)
• Consumption Coughing and chronic weight loss
• Dissemination
• Extrapulmonary TB (lymph nodes, kidneys, bones,
  genital tract, brain, meninges)

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Pneumonia

• Bacterial, viral or fungal infection
• Inflammation of the lung with fluid filled alveoli

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Bacterial Pneumonia

• Streptococcus pneumoniae
• 2/3 of all pneumonia
• High risk - old age, season, underlying
• viral infection, diabetes, alcohol and narcotic
  use
• Variable capsular antigen
• Vaccines
• Mycoplasma pneumoniae
• Legionella pneumophila

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Mycoplasma pneumoniae

• Smallest known bacteria
• No cell wall
• Walking pneumonia atypical pneumonia

Legionella pneumophila

• Less common but still a serious infection
• Survives in natural habitat (tap water, cooling
• towers, spas, etc.)
• Opportunistic disease