Respiratory System Infections: Microbiology Study Guide

Respiratory System Infections

Overview

The respiratory system is frequently affected by a variety of microbial pathogens, including viruses, bacteria, and fungi. These infections range from mild upper respiratory tract illnesses to severe, life-threatening diseases. Understanding the causative agents, epidemiology, transmission, symptoms, pathogenesis, and treatment options is essential for microbiology students.

Viral Respiratory Infections

Respiratory Syncytial Virus (RSV)

RSV is a major cause of respiratory illness in infants and young children, and can be dangerous in immunocompromised individuals.

• Causative Agent: Respiratory syncytial virus (RSV), enveloped, single-stranded RNA virus, Pneumoviridae family.

• Epidemiology: Common among children under age 5; severe in premature infants and immunocompromised patients.

• Transmission & Prevention: Spread by respiratory droplets and fomites; hand washing and isolation practices are key preventive measures.

• Signs & Symptoms: Coughing, sneezing, fever, and lower respiratory symptoms; wheezing may also occur.

• Pathogenesis & Virulence Factors: Infects the respiratory epithelium, causing cell death and inflammation.

• Diagnosis & Treatment: Antigen-detection tests; supportive therapy is mainstay.

Adenovirus Infections

Adenoviruses cause a range of respiratory illnesses and can also affect other organ systems.

• Causative Agent: Over 50 types of adenoviruses; double-stranded DNA viruses.

• Epidemiology: Infections occur year-round; outbreaks in military and school settings.

• Transmission & Prevention: Respiratory droplets and fomites; hand washing and avoiding close contact.

• Signs & Symptoms: Most commonly cause respiratory symptoms, but can also cause conjunctivitis, diarrhea, and cystitis.

• Pathogenesis & Virulence Factors: Attach to host cells and replicate in epithelial cells.

• Diagnosis & Treatment: Antigen detection or polymerase chain reaction (PCR); supportive therapy.

Influenza

Influenza viruses are responsible for seasonal epidemics and pandemics, with significant morbidity and mortality.

• Causative Agent: Influenza types A, B, and C; enveloped, single-stranded RNA viruses, Orthomyxoviridae family.

• Epidemiology: Endemic worldwide; can cause epidemics and pandemics.

• Transmission & Prevention: Respiratory droplets and fomites; prevented by seasonal vaccination and hygiene.

• Signs & Symptoms: Sudden onset fever, chills, muscle aches, headache, sore throat, and cough.

• Pathogenesis & Virulence Factors: Viral hemagglutinin and neuraminidase facilitate entry and release from host cells.

• Diagnosis & Treatment: Rapid antigen tests; antiviral drugs (oseltamivir, zanamivir) if given early.

Severe Acute Respiratory Syndrome (SARS)

SARS is caused by a coronavirus and can lead to severe respiratory illness.

• Causative Agent: SARS-CoV, enveloped, single-stranded RNA virus, Coronaviridae family.

• Epidemiology: First outbreak in 2002; affects people of all ages.

• Transmission & Prevention: Respiratory droplets and fomites; hygiene and isolation are important.

• Signs & Symptoms: Severe respiratory symptoms, fever, and cough.

• Pathogenesis & Virulence Factors: Virus infects respiratory epithelium and triggers immune response.

• Diagnosis & Treatment: PCR and cell culture; supportive care.

Bacterial Respiratory Infections

Otitis Media

Otitis media is a middle ear infection, often caused by bacteria and common in children.

• Causative Agent: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis.

• Epidemiology: Most children in the U.S. have at least one infection by age 3.

• Transmission & Prevention: Vaccination and hygiene; reducing exposure to respiratory pathogens.

• Signs & Symptoms: Ear pain, fever, irritability, and fluid or blood from the ear.

• Pathogenesis & Virulence Factors: Accumulation of mucus and bacteria in the middle ear.

• Diagnosis & Treatment: Antibiotics and pain management.

Pertussis (Whooping Cough)

Pertussis is a highly contagious respiratory disease, especially dangerous for infants.

• Causative Agent: Bordetella pertussis, Gram-negative bacterium.

• Epidemiology: Most cases in children; outbreaks occur in susceptible populations.

• Transmission & Prevention: Respiratory droplets; vaccination is key.

• Signs & Symptoms: Catarrhal stage (mild symptoms), paroxysmal stage (severe coughing fits).

• Pathogenesis & Virulence Factors: Toxins damage ciliated epithelium, impairing mucus clearance.

• Diagnosis & Treatment: Bacterial culture and PCR; antibiotics (macrolides).

Tuberculosis

Tuberculosis is a chronic bacterial infection that primarily affects the lungs.

• Causative Agent: Mycobacterium tuberculosis, acid-fast, Gram-positive bacterium.

• Epidemiology: Most common in Africa and Asia; latent and active forms.

• Transmission & Prevention: Airborne droplets; BCG vaccine for prevention.

• Signs & Symptoms: Persistent cough, blood-tinged sputum, fever, night sweats.

• Pathogenesis & Virulence Factors: Bacteria survive in macrophages, forming granulomas.

• Diagnosis & Treatment: Mantoux tuberculin skin test, chest X-ray, sputum culture; multi-drug therapy.

Typical Pneumonia

Pneumonia is an infection of the lung parenchyma, with typical and atypical forms.

• Disease: Pneumococcal pneumonia (Streptococcus pneumoniae), Haemophilus pneumonia (Haemophilus influenzae).

• Epidemiology: Most common cause of community-acquired pneumonia worldwide.

• Transmission & Prevention: Respiratory droplets; vaccination and hygiene.

• Signs & Symptoms: Sudden onset fever, chills, productive cough, chest pain.

• Pathogenesis & Virulence Factors: Capsule protects against phagocytosis; toxins damage lung tissue.

• Diagnosis & Treatment: Sputum culture, chest X-ray; antibiotics.

Atypical Pneumonia

Atypical pneumonia is caused by organisms that do not typically cause classic pneumonia symptoms.

• Disease: Walking pneumonia (Mycoplasma pneumoniae), Chlamydophila pneumoniae, Legionnaires' disease (Legionella pneumophila), Pontiac fever.

• Epidemiology: Common in children and young adults; outbreaks in close-contact settings.

• Transmission & Prevention: Respiratory droplets; hygiene and avoiding contaminated water sources.

• Signs & Symptoms: Mild symptoms, dry cough, fatigue, muscle aches.

• Pathogenesis & Virulence Factors: Specialized attachment structures; toxins and immune evasion.

• Diagnosis & Treatment: PCR, serology; macrolide antibiotics.

Fungal Respiratory Infections

Blastomycosis (Chicago Disease)

Blastomycosis is a fungal infection caused by inhalation of spores, primarily affecting the lungs.

• Causative Agent: Blastomyces dermatitidis or Paracoccidioides brasiliensis.

• Epidemiology: Endemic in North America and South America.

• Transmission & Prevention: Inhalation of spores; avoiding exposure is best prevention.

• Signs & Symptoms: Fever, headache, cough, muscle aches, chest pain.

• Pathogenesis & Virulence Factors: Fungi evade immune response and cause granulomatous inflammation.

• Diagnosis & Treatment: Fungal culture, serology; antifungal drugs (itraconazole, amphotericin B).

Coccidioidomycosis (Valley Fever)

Coccidioidomycosis is caused by inhalation of Coccidioides spores, leading to respiratory symptoms.

• Causative Agent: Coccidioides immitis and Coccidioides posadasii.

• Epidemiology: Endemic in southwestern U.S. and northern Mexico.

• Transmission & Prevention: Inhalation of fungal spores; no preventive measures beyond avoiding exposure.

• Signs & Symptoms: Fever, chest pain, cough, headache, joint pain, rash.

• Pathogenesis & Virulence Factors: Fungi evade immune response and cause granulomas.

• Diagnosis & Treatment: Fungal culture, serology; antifungal drugs.

Histoplasmosis

Histoplasmosis is a fungal infection caused by inhalation of Histoplasma capsulatum spores.

• Causative Agent: Histoplasma capsulatum.

• Epidemiology: Common in populations exposed to bird or bat droppings.

• Transmission & Prevention: Inhalation of spores; avoiding exposure is key.

• Signs & Symptoms: Fever, chest pain, cough, fatigue, chills.

• Pathogenesis & Virulence Factors: Fungi survive in macrophages and cause granulomas.

• Diagnosis & Treatment: Fungal culture, serology; antifungal drugs.

Aspergillosis

Aspergillosis is caused by Aspergillus species, especially in immunocompromised patients.

• Causative Agent: Aspergillus species, especially A. fumigatus.

• Epidemiology: Common in immunocompromised patients.

• Transmission & Prevention: Inhalation of spores; no vaccine available.

• Signs & Symptoms: Cough, chest pain, difficulty breathing.

• Pathogenesis & Virulence Factors: Fungi invade lung tissue and blood vessels.

• Diagnosis & Treatment: Fungal culture, imaging; antifungal drugs.

Pneumocystis Pneumonia

Pneumocystis pneumonia is a fungal infection, often seen in immunocompromised patients.

• Causative Agent: Pneumocystis jirovecii.

• Epidemiology: Most healthy children exposed by age 3; severe in immunocompromised patients.

• Transmission & Prevention: Person-to-person transmission; no vaccine.

• Signs & Symptoms: Fatigue, dyspnea, dry cough.

• Pathogenesis & Virulence Factors: Fungi attach to alveolar cells, causing inflammation.

• Diagnosis & Treatment: Fungal culture, PCR; trimethoprim-sulfamethoxazole.

Summary Table: Key Respiratory Pathogens

The following table summarizes the main causative agents, epidemiology, transmission, symptoms, pathogenesis, and treatment for major respiratory infections covered above.

Disease	Causative Agent	Transmission	Symptoms	Treatment
RSV	Respiratory syncytial virus	Droplets, fomites	Cough, wheezing	Supportive
Influenza	Influenza A/B/C	Droplets, fomites	Fever, aches, cough	Antivirals
Pertussis	Bordetella pertussis	Droplets	Severe cough	Antibiotics
Tuberculosis	Mycobacterium tuberculosis	Airborne	Cough, blood sputum	Multi-drug
Blastomycosis	Blastomyces dermatitidis	Inhalation	Fever, cough	Antifungals

Additional info: This summary table is inferred for exam review purposes and does not cover all pathogens in detail.