Chapter 22 Respiratory system diseases

Structures of the Respiratory System

• Overview: The respiratory system consists of the upper and lower respiratory systems, each containing various significant structures.
  • Upper Respiratory System: Includes the nasal cavity, pharynx, larynx, and trachea.
  • Lower Respiratory System: Comprises the bronchi, bronchioles, and lungs (right and left), as well as the diaphragm.

Normal Microbiota of the Respiratory System

• Upper vs. Lower Respiratory System:
  • Lower respiratory system typically devoid of microorganisms.
  • Upper respiratory system hosts normal microbiota which help limit pathogenic growth and may act as opportunistic pathogens (e.g., Hemophilus, Streptococcus, Staphylococcus).

Bacterial Diseases of the Upper Respiratory System

• Streptococcal Respiratory Diseases:

  • Signs and Symptoms: Sore throat, difficulty swallowing, potential progression to scarlet or rheumatic fever.
  • Pathogen: Caused by Group A Streptococcus (S. pyogenes).
  • Virulence Factors: Includes M proteins, hyaluronidase capsules, streptokinases, pyrogenic toxins, and streptolysins.
  • Pathogenesis: Infections occur when normal microbiota are depleted or when body’s immune responses are impaired.
  • Epidemiology: Spread via respiratory droplets, more frequent in winter and spring.
  • Diagnosis and Treatment: Often confused with viral pharyngitis; treated with penicillin or erythromycin for resistant strains.

• Diphtheria:

  • Signs and Symptoms: Sore throat, fluid oozing, pseudomembrane obstructing airways.
  • Pathogen: Corynebacterium diphtheriae, which produces diphtheria toxin leading to cell death.
  • Transmission: Person-to-person via respiratory droplets; carriers may be asymptomatic.
  • Diagnosis and Treatment: Identification of pseudomembrane, treated with antitoxin and antibiotics. Prevention via vaccination (DPT).

• Common Cold:

  • Signs and Symptoms: Sneezing, congestion, sore throat, malaise. Duration 7-12 days.
  • Pathogens: Primarily rhinoviruses, with other viral infections contributing.
  • Transmission: Coughing/sneezing, fomites, person-to-person.
  • Treatment: Supportive and palliative; pleconaril may reduce duration of symptoms.

• Sinusitis and Otitis Media:

  • Signs and Symptoms: Sinusitis involves pain and pressure in sinuses; otitis media presents as ear pain.
  • Pathogens: Various bacteria (e.g., S. pneumoniae, S. aureus).
  • Pathogenesis: Infections follow after colds; sinusitis common in adults, otitis media in children.
  • Treatment: Symptoms are often diagnostic; managed with antibiotics.

Bacterial Diseases of the Lower Respiratory System

• Bacterial Pneumonias:

  • Signs and Symptoms: Inflammation of lungs with fluid-filled alveoli and bronchioles, typically severe. Can be lobar pneumonia affecting whole lobes.
  • Virulent Agents: Include Streptococcus pneumoniae (Pneumococcal pneumonia), Mycoplasma pneumoniae (Atypical pneumonia), Klebsiella pneumoniae, and others.
  • Pathogenesis: Involves inhalation or blood transmission; pneumonia can be fatal, particularly in adults.

• Pneumococcal Pneumonia:

  • Signs and Symptoms: Fever, cough, chest pain, rapid breathing.
  • Pathogen: S. pneumoniae with virulence factors like a capsule and pneumolysin.
  • Diagnosis and Treatment: Treated with vancomycin; vaccination is preventive.

• Tuberculosis (TB):

  • Pathogenesis: Mycobacterium tuberculosis remains viable in aerosol drops; causes primary, secondary, and disseminated TB.
  • Symptoms: Persistent cough, weight loss, fever; can lead to severe complications.
  • Diagnosis: Tuberculin skin test, chest X-ray, etc.
  • Treatment: Combination therapy with isoniazid, rifampin, etc.

Viral Diseases of the Respiratory System

• Influenza:

  • Signs and Symptoms: Sudden fever, cough, body aches.
  • Pathogen: Influenza viruses (types A and B), which undergo antigenic drift and shift.
  • Diagnosis and Treatment: Often diagnosed via symptoms; antiviral medications available; yearly vaccination critical for prevention.

• COVID-19:

  • Causative Agent: SARS-CoV-2, an emerging mutated coronavirus.
  • Signs and Symptoms: Persistent dry cough, fever, malaise, respiratory distress.
  • Transmission: Person-to-person via aerosols, droplets.
  • Treatment and Prevention: Supportive care, use of remdesivir, vaccines like Pfizer and Moderna now available.

• Respiratory Syncytial Virus (RSV):

  • Signs and Symptoms: Fever, rapid breathing, cough in infants; mild in adults.
  • Pathogen: RSV, common childhood respiratory disease.
  • Treatment: Supportive and medication such as ribavirin; preventive measures critical.
  • Epidemiology: Most prevalent in late winter, affecting infants and the immunocompromised.

Mycoses of the Lower Respiratory System

• Histoplasmosis:

  • Causative Agent: Histoplasma capsulatum.
  • Symptoms: Often mild unless in immunocompromised individuals.
  • Treatment: Managed with antifungal medications.

• Pneumocystis Pneumonia:

  • Causative Agent: Pneumocystis jirovecii.
  • Symptoms: Difficulty breathing and hypoxia; common in AIDS patients.
  • Treatment: Trimethoprim and sulfamethoxazole, though prevention is challenging.