Respiratory system infections

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Respiratory system infections Upper,
lower Severity tends to depend on Where
infection is established (and whether
it spreads) Age and robustness of immune
system Virulence factors of organism
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Respiratory system environment is diverse

• Upper respiratory system
• Nose, pharynx, associated structures
• Purpose to take in, warm and moisten air
• Most common site of infections
• Lower respiratory system
• Larynx, trachea, bronchi, alveoli
• Purpose ventilation, gas exchange

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Geography of the respiratory system (and sites of
infection)
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Protective structures of the respiratory
system Mucous membranes Hairs ciliated
epithelia Lymphoid tissues (tonsils) Mucociliar
y escalator keeps microbes out of lower
respiratory tract Alveolar macrophages IgA
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Most of the respiratory system is NOT
colonized by normal flora (p. 564) Generally
confined to nose, nasopharynx and pharynx
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Upper respiratory system

• Pharyngitis, laryngitis, tonsillitis, etc.
• Can be caused by bacteria, viruses or both
• Usually self-limiting
• S pyogenes is an important pathogen
• Resistant to immune system
• Produces toxins (superantigens)
• Immune reaction (glomerulonephritis, rheumatic
  fever)

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Diphtheria disease also caused by
exotoxin picked up by some cells but not
others inhibits protein synthesis (kills
cells) Vaccines have been available for a long
time neutralize toxin Passive immunization is
available
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Microbial infections of associated areas Otitis
media Conjunctivitis Sinusitis Both bacterial
and viral infectious agents have been found
(implications for treatment?) Viral infections-
rhinitis, pharyngitis, etc. too many types!
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Lower respiratory infections

• Usually stopped by immune/mechanical means
• Pneumonia (inflammation of lung)
• Tuberculosis (chronic inflammation)
• Whooping cough (kills ciliated cells)

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Many infectious agents cause pneumonia

• Bacterial
• Legionella- spreads in ventilation systems
• Mycoplasma (walking pneumonia)
• very unusual microbes
• Pneumococcus (S. pneumoniae)
• Encapsulated causes inflammation
• Can spread and cause endocarditis, meningitis,
  septicemia

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Diagnosis by culture X-ray
Which lung is affected?
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Tuberculosis

• Gram bacterium infects macrophages
• Hypersensitivity reaction damages lung tissue
• Many people are infected most do not develop TB
• Mantoux test detects prior exposure
• Aggressive and long-term antibiotic treatment is
  required

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Several viral pneumonias also described

• Adenovirus
• Complications of influenza
• Affects many types of animals (wild and
  domesticated) source of genetic exchange
• Can frustrate immune system due to constant
  antigen change
• RSV (respiratory syncytial virus)
• Especially dangerous for infants
• Tends to recur

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Mechanisms of viral respiratory infections

• Influenza
• kills epithelial cells spreads rapidly to other
  cells
• RSV
• Kills epithelial cells which can block
  respiratory passages

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Hantavirus pulmonary syndrome

• Spread by inhalation of dust contaminated by mice
• High fatality rate (40)
• No person-to-person spread
• Infects capillary epithelium blood vessel damage
  and shock

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Fungal infections are rare in healthy people

• Immune system usually controls growth
• Soil source is typical
• Can be accidental (after an earthquake, e.g.,
  Coccidioides immitis, Valley fever

p. 591
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Histoplasma, a dimorphic fungus

• Spread by droppings from birds or bats (do not
  get sick themselves)
• spelunkers disease
• TB-like symptoms
• Recovery usually spontaneous, but slow
• What would be preferred drug treatment?

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Summary

• Respiratory system can host a variety of microbes
• Normal flora in restricted areas
• Susceptibility depends on age, immune system
• Some organisms are adept at evading immune system
• Damage generally due to cytotoxicity and
  inflammation
• Vaccines are available for some organisms