Infectious Diseases of the Respiratory System

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Infectious Diseases of the Respiratory System
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Infections of the Respiratory tract

• Most common entry point for infections
• Upper respiratory tract
• nose, nasal cavity, sinuses, mouth, throat
• Lower respiratory 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 deep in the lungs.
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Other Protective Mechanisms

• Nasal hair, nasal turbinates
• Mucus
• Involuntary responses (coughing)
• Secretory IgA
• Immune cells

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Selected Bacterial Infections

• Pharyngitis
• Group A Strep - Streptococcus pyogenes
• (Many viruses also cause this)
• Pneumonia - Streptococcus pneumoniae
• Diphtheria - Corynebacterium
  diphtheriae
• Tuberculosis - Mycobacterium tuberculosis
• Whooping cough - Bordetella pertussis

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Streptococcus pyogenes

• Gram positive streptococci
• Carried and transmitted from the throat
• In Respiratory secretions

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Group A Strep

• Capsule -resistant to phagocytosis
• Enzymes damage host cells
• M protein adhesin

The M protein has many antigenic varieties and
thus, different strain of S.pyogenes cause
repeat infections
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Strep Throat

• Fever
• Tonsillitis
• Enlarged lymph nodes
• Middle-ear infection

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Infected Middle Ear(otitis media)
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Scarlet Fever
Caused by Erythrogenic Toxin secreted by S.
pyogenes
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Scarlet Fever

• The erythrogenic
• toxin is coded by a gene
• lysogenic bacteriophage
• within the genome of
• S. pyogenes
• Rash is an inflammatory reaction to the toxin

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Bacterial Pneumonia
Bacterial, viral or fungal infection can cause
Inflammation of the lung with fluid filled
alveoli
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Streptococcus pneumoniae

• Pneumococcus
• Encapsulated
• Often secondary infection following influenza
  virus

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Bacterial Pneumonia

• Streptococcus pneumoniae
• 2/3 of all pneumonia
• Risk Factors- old age, season, underlying
• viral infection, diabetes, alcohol and narcotic
  use
• Variable capsular antigen
• Purified component (capsule) vaccine
• Others that cause pneumonia
• Mycoplasma pneumoniae
• Legionella pneumophila

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Diphtheria
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The Diphtheria Outbreak of Nome, Alaska, 1925
Heroic Alaska Dog Teams
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(No Transcript)
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Nome, Alaska 1900
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Nome, Alaska, Balto and Gunnar Kaasens Team
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The 34th Annual Iditarod Race
Commemorating the 1925 Emergency Delivery of
Diphtheria Serum to Nome, Alaska
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Diphtheria

• Transmitted by droplets or fomites
• Infects the upper respiratory tract
• Begins with severe sore throat, low-grade fever
  and swollen lymph nodes or with skin rash, 1-6
  days after infection

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Corynebacterium diphtheriae

• Aerobic Gram bacillus
• Toxin inhibits protein synthesis of cells to
  which it binds
• Destroyed cells and WBC form "pseudomembrane"
  which blocks airways

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Diphtheria
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An AB toxin

• B binding subunit
• A active subunit
• which binds to and inhibits a eucaryotic
  ribosomal translation factor
• Vaccine is diphtheria toxoid

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Corynebacterium diphtheriae

• To produce toxin, C. dithpheriae must be infected
  with a bacteriophage carrying the toxin gene

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Bordetella pertussis

• Gram negative cocco-bacillus
• Capsule
• Adherence to ciliated cells
• Pertussis toxin is A-B toxin

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Pertussis (Whooping Cough)

• Cough
• Violent coughing followed by whooping sound
• Vaccine it is made of
• purified components
• Not lifelong immunity adult carriers

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Mycobacterium tuberculosis

• Acid-fast bacillus complex cell wall with cord
  factor
• Causes TB lungs
• bones, other organs
• Airborne, (milk, v. rare)

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Mycobacterium tuberculosis

• Thick lipid coat
• of Mycolic fatty acids
• Grows very slowly
• Resists killing by macrophages and grows in them

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Tubercule formation
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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Tuberculosis

• Elimination requires long antibiotic treatment
  with cocktail of antibiotics because
• of the resistance that develops.

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Multi-Drug ResistantMycobacterium tuberculosis
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TB Skin Test
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Virus infections

• Respiratory syncytial virus (RSV)
• Influenza virus

Fungal Infections

• Coccidiodomycosis (Valley Fever)
• Coccidioides immitis

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Respiratory Syncytial Virus

• Enveloped (membrane) RNA virus
• Spread by respiratory droplets
• Community outbreaks in late fall to spring
• Upper respiratory tract infection epithelial
  cells
• May be fatal in infants

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Influenza Virus An enveloped RNA virus
Structure
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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 parts bind to host
• cells of the respiratory mucosa
• Different parts are
• recognized by the host antibodies
• Subject to changes

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

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Influenza

• Epidemics and pandemics, mostly in winter
• Upper respiratory tract infection epithelial
  cells
• Multivalent killed virus vaccine with strains
  from the previous year (Grown in embryonated
  eggs)
• Bird flu (H5N1) pandemic in birds

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Coccidioides immitis

• Soil fungus in American Southwest
• Cause of Valley Fever
• Highly infectious

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Valley Fever is an Endemic Disease
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Coccidioides immitis Life Cycle
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Coccidioides immitis

• Valley Fever usually a flu-like illness
• Can spread to bones, skin, meninges
• 100,000 new cases/yr in SW