In-Depth Notes on Respiratory Infections ch 21

Overview of Respiratory Infections

• Genesis 2:7: The biblical reference to the respiratory process.

Types of Respiratory Infections

• Diversity: Respiratory infections can range from trivial (like common colds) to fatal (like pneumonia).

• Classification:

  • Upper Respiratory Infections (URI):

  • Examples: Common colds, rhinitis, pharyngitis.

  • Typically clear up without treatment in about a week.

  • Lower Respiratory Infections (LRI):

  • Examples: Pneumonia, tuberculosis.

  • Often serious and may result in death.

Anatomy of the Respiratory System

• Functionality:

  • Replenishes oxygen (O2) and releases carbon dioxide (CO2).

  • Vocal cords are used for producing sound.

  • Nose detects odors.

• Respiratory Tracts:

  • Upper Respiratory Tract: Nose, nasal cavity, throat (pharynx), epiglottis.

  • Lower Respiratory Tract: Larynx, trachea, bronchi, lungs.

• Pathways for Pathogens: Eyes, ears, and other regions can serve as portals for pathogens to enter the body.

Upper Respiratory Tract Details

• Anatomy:

  • Lined with mucous membranes.

  • Goblet Cells: Produce mucus, which traps airborne particles.

  • Mucociliary Escalator: Mechanism to expel mucus from the respiratory tract and maintain sterility in the lower tract.

• Immune Response:

  • Tonsils act as lymphoid organs, crucial for immune response.

  • Can become infected, leading to conditions like tonsillitis.

Common Upper Respiratory Infections

• Rhinitis: Usually viral, inflammation of the nose.

• Pharyngitis: Sore throat, associated with viral infections.

• Epiglottitis: Inflammation of the epiglottis that can be life-threatening.

Lower Respiratory Tract Infections

• Typically sterile; structures include:

  • Larynx, trachea, bronchi, and lungs.

• Common Conditions:

  • Laryngitis: Inflammation of the larynx.

  • Bronchitis: Often viral, can also result from smoking.

  • Bronchiolitis: Infection of small airways; often viral.

  • Pneumonia: Can fill alveoli with pus and fluid, leading to difficulty breathing.

• Pleurisy: Inflammation of the lung lining.

Pneumococcal Pneumonia

• Causative Agent: Streptococcus pneumoniae:

  • Accounts for ~60% of pneumonia in adults requiring hospitalization.

  • Thick polysaccharide capsule aids virulence.

  • Symptoms include cough, fever, chest pain, and production of rust-colored sputum.

• Pathogenesis:

  • Inhalation leads to rapid multiplication in alveoli and inflammatory responses.

  • Can cause complications: pleurisy, sepsis, endocarditis, meningitis.

• Epidemiology:

  • 30% of healthy individuals can carry it.

  • Risk increases with compromised immune systems (e.g., due to excessive alcohol use, chronic diseases).

• Treatment:

  • Antibiotics (penicillin, erythromycin) are effective if given early.

  • Vaccines available for many serotypes.

Klebsiella Pneumonia

• Causative Agent: Klebsiella pneumoniae, a common hospital-acquired pathogen.

  • Symptoms include cough, fever, and bloody, mucoid sputum.

• Pathogenesis:

  • Infection via inhalation or contact, heavy colonization in throat.

  • Capsule enhances virulence and triggers tissue damage.

• Epidemiology:

  • Widespread in nature and can become resistant to antibiotics.

Mycoplasmal Pneumonia

• Often termed Walking Pneumonia, typically mild and common in college students.

• Causative Agent: Mycoplasma pneumoniae, characterized by a lack of cell wall.

  • Symptoms include gradual onset of fever and cough, with potential for otitis media.

• Pathogenesis:

  • Slow growth and limited cells can lead to infection.

• Epidemiology:

  • Spread via aerosolized droplets, immunity not permanent, leading to re-infection.

Viral Infections of the Lower Respiratory System

• Importance: RNA viruses, especially Influenza, pose significant threats.

• Influenza:

  • Infections affect ~20% of the population annually.

  • Symptoms include fever, muscle pain, sore throat.

• Causative Agents:

  • Influenza A is the most severe, with antigenic variations leading to seasonal flu and potential pandemics.

• Prevention and Treatment:

  • Antivirals and annual vaccines are crucial; effectiveness varies with virus mutations.

1. Describe the mucociliary escalator:

   • The mucociliary escalator is a defense mechanism of the upper respiratory tract consisting of ciliated epithelial cells and mucus-secreting goblet cells. Mucus traps inhaled particles and pathogens, while cilia beat in a coordinated manner to move the mucus upwards towards the throat, where it can be swallowed or expelled, thus helping to keep the airways clear of debris and pathogens.

2. List the parts of the respiratory system that are normally free of bacterial microbiota:

   • The lower respiratory tract, specifically the structures like the larynx, trachea, bronchi, and lungs, are normally considered sterile and free of bacterial microbiota under healthy conditions.

3. Describe the primary opportunistic pathogen commonly found in the nose:

   • Staphylococcus aureus is a common opportunistic pathogen found in the nasal cavity. It can reside asymptomatically in the nose but has the potential to cause infections, especially in immunocompromised individuals.

4. For each of the following diseases, list the cause, major characteristics, and modes of transmission:

   • Influenza:

     • Cause: Influenza virus (specifically Influenza A and B).

     • Major Characteristics: Causes fever, muscle pain, sore throat, and cough. Symptoms can lead to severe respiratory illness, especially in vulnerable populations.

     • Modes of Transmission: Spread via aerosolized droplets from coughing or sneezing, or by touching surfaces contaminated with the virus.

   • Pneumococcal pneumonia:

     • Cause: Streptococcus pneumoniae.

     • Major Characteristics: Symptoms include cough, fever, chest pain, and production of rust-colored sputum. Can lead to serious complications.

     • Modes of Transmission: Spread through respiratory droplets. Carriers can transmit the bacteria without showing symptoms.

   • Klebsiella pneumonia:

     • Cause: Klebsiella pneumoniae.

     • Major Characteristics: Symptoms include cough, fever, and jelly-like mucoid sputum. Often associated with hospital-acquired infections.

     • Modes of Transmission: Typically spread through inhalation or contact with contaminated surfaces.

   • Mycoplasma pneumonia (Walking pneumonia):

     • Cause: Mycoplasma pneumoniae.

     • Major Characteristics: Typically mild, gradual onset of fever and cough, can lead to otitis media.

     • Modes of Transmission: Spread through aerosolized droplets; immunity is not permanent, leading to potential reinfections.

5. Describe the virulence factors for:

   • Pneumococcal pneumonia:

     • The thick polysaccharide capsule that protects the bacteria from phagocytosis and enhances its virulence.

     • The ability to produce harmful toxins that damage host tissues, contributing to severe inflammation and immune response.

   • Klebsiella pneumonia:

     • The presence of a polysaccharide capsule that aids in virulence and triggers tissue damage, making the bacteria highly resistant to phagocytosis.

   • Influenza:

     • Antigenic variation of the virus allows it to evade the immune response, leading to seasonal outbreaks and potential pandemics.

6. Identify the bacteria that cause pneumonia and describe their key features:

   • Streptococcus pneumoniae: Most common cause; has a thick capsule and can be rapidly multiplying in alveoli, leading to inflammation.

   • Klebsiella pneumoniae: Often associated with hospital-acquired infections; known for mucoid sputum and resistance to antibiotics.

   • Mycoplasma pneumoniae: Lacks a cell wall, making it resistant to certain antibiotics; causes atypical pneumonia and is commonly seen in younger populations.

   • Haemophilus influenzae: Can cause pneumonia and is particularly concerning in individuals with underlying lung conditions.