Chapter 24 Microbial Infection of the Respiratory Systems

Strep Throat

• Causative Agent:

  • Streptococcus pyogenes

• Signs/Symptoms:

  • Pharyngitis, red patches on throat, fever, swollen lymph nodes

• Pathogenesis: Virulence factors

  • Streptokinase - digest fibrin

  • C5a peptidase - digest C5a. No inflammation, no phagocytosis

  • Capsule - avoid recognition and attachment by phagocytes

  • M-protein - avoid recognition and attachment by phagocytes. Digests C3B, preventing opsonization. Opsonization enhances phagocytosis.

  • Protein G - binds to FC region of antibody, located on the surface of the bacteria. SIMILAR TO PROTEIN A. Prevents attachment which prevent phagocytosis

• Complications: SPE’s – Streptococcal pyrogenic exotoxins – cause severe complications

  • Acute glomerulonephritis, Scarlet fever, Rheumatic fever, “Flesh-eating” Strep

• Epidemiology:

  • Transmission via respiratory droplets

• Prevention:

  • No vaccine; Avoid crowds

• Treatment:

  • Antibiotics

  • Penicillin

Tuberculosis

• Causative agent:

  • Mycobacterium tuberculosis

• Signs/Symptoms:

  • Fever, cough, weight loss

• Pathogenesis:

  • Resistance to digestion by phagocytes systemic infection

  • Characterized by tubercules (granulomas) in the lung

• Epidemiology:

  • Transmission via respiratory droplets

• Treatment:

  • 3+ antibiotics for 6 months

  • Isoniazid, ethambutol

  • These target mycolic acid synthesis

• Preventions:

  • BCG vaccine (not used in U.S.), not an effective vaccine for adults

Pathogenesis of Tuberculosis.

1. Tubercle bacilli that reach the alveoli of the lung → ingested by macrophages → often some survive. Infection is present, but no symptoms of disease

2. TB multiply in macrophages → Chemotactic response → brings in macrophages and other defensive cells to area.

   • Macrophages are not successful in destroying bacteria → release enzymes and cytokines that cause damaging inflammation.

3. Disease symptoms appear after a few weeks → macrophages die → macrophage death releases TB and form a caseous center.

4. When this ruptures, this causes TB.

Influenza (RNA VIRUS)

• Causative agent:

  • Influenza virus

• Signs / Symptoms:

  • Headache, fever, chills, muscle aches

  • Cough, fatigue

• Pathogenesis:

  • Virus infects and kills respiratory cells

  • 2nd infections: bacterial agents- pneumonia

• Virus antigens: (spike proteins)

  • Hemagglutinin (H) (ATTACHMENT TO HOST CELLS)

  • Neuraminidase (N) (RELEASES VIRIONS)

• Epidemiology:

  • Respiratory droplets

  • fomites

• Prevention:

  • Influenza vaccine - Given each year

  • Hand washing

• Treatment:

  • Block neuraminidase

Antigenic Drift

Random mutations in the H and N spike

HAPPENS EVERY YEAR

Antigenic Shift

At least 2 or more viruses (influenza) due to genetic recombination occur. This is an EXCHANGE of RNA strands

DOES NOT HAPPEN OFTEN

Common Cold

• Causative agents:

  • Rhinoviruses, Coronaviruses, Enterovirus

• Signs/Symptoms:

  • Sore throat, “malaise”, Runny nose, cough

• Pathogenesis:

  • Virus infects upper respiratory cells

  • Triggers inflammation

• Epidemiology

  • Transmission via airborne droplets or contact (hand to
    eye or nose contact)

• Prevention

  • Handwashing!!

  • Don’t rub eyes or nose!

• Treatment:

  • None

Coronavirus Disease 2019 (COVID-19)

• Causative agent:

  • severe acute respiratory syndrome
    coronavirus 2 (SARS-CoV-2)

• Signs / Symptoms: may appear 2-14 days after exposure to the virus

  • Cough, Shortness of breath or difficulty breathing, Fever, Chills, Muscle pain, Sore throat, New loss of taste or smell

• Pathogenesis: not fully understood

  • Infect cells in respiratory tract

  • Damages cells and strong immune response

• Epidemiology: not fully understood

  • Transmitted by respiratory droplets duringcclose person-to-person contact

  • Indirect

• Prevention:

  • Handwashing

  • Social distancing

  • Face coverings

• Treatment:

  • Research to develop anti-viral drugs and vaccines.