ch21 - respiratory system infections CONTINUE

Respiratory System Infections

• Most prevalent type of infection

  • Due to ease of transmission

    • Inanimate objects – phones, keyboards, doorknobs

    • Respiratory droplets (inhalation)

      • Nasal spray (sneezes) – 5-6 ft

• Varies from annoyance to deadly

Divided into infections of

1. Upper respiratory (head/neck)

• Very common

• Uncomfortable but not life threatening

• Have normal microbiota – nose, throat

  • Streptococci very common in throat

  • ~30% of healthy people carry Staphylococcus aureus in their nose

• Sterile sites

  • Conjunctiva

  • Sinuses

  • Tear ducts

  • Middle ear

2. Lower respiratory (Chest)

• More serious, can be life-threatening

• No normal microbiota

• Defenses

  • IgA, macrophages, mucociliary escalator

Bacterial Infections of Upper Respiratory System

• Generally trivial and do not require treatment

• More serious, and can cause serious complications in those immunocompromised, very young and the very old

pinkeye, earache, and sinus infections

• Occurrence is common, often from same agent

• Common secondary infections

• Common causative agents:

  • Streptococcus pneumoniae

  • Haemophilus influenzae

pinkeye

conjunctivitis – bacterial or viral pathogen

• Tears, redness of conjunctiva, swollen eyelids

• Large amounts of pus

  • Viral conjunctivitis less pus discharge and eye swelling

• Bacterial conjunctivitis highly contagious

earache

Ears

• Outer ear – has normal microbiota

  • Otitis externa (infection of outer ear)

    • Causes: S. aureus, C. albicans and Gram (–) opportunistic pathogens (Proteus and P. aeruginosa)

• Inner and middle ear are sterile

  • Otitis media (infection of middle ear)

    • Common in young children

    • Mild fever, severe earache due to fluids in eardrum

    • Pressure may cause eardrum to rupture

sinus infections

Sinus – normally sterile

• Sinusitis – sinus infection

• Inflammation leads to symptoms

• Facial pain, pressure; headache, malaise, thick green nasal discharge may develop

Streptococcal Pharyngitis (“strep throat”)

Causative Agent = Streptococcus pyogenes

• Gram-positive streptococci

  • Group A streptococcus (GAS)

• β-hemolytic on blood agar

  • Complete hemolysis of RBCs

  • Systemic → hemolytic anemia (deadly)

• Virulence due to virulence factors

  • Adhesins, avoidance of host defenses

    • Capsules

    • M protein

  • Exotoxins (pyogenic)

    • Pus-forming

Spread by respiratory droplets or contaminated food

Characterized by:

• Sore throat, difficulty swallowing, fever

• Red throat with pus patches

Confirmation via diagnostic tests and throat culture

• Rapid antigen test – using antibodies to detect bacteria

• Throat culture - growing bacteria

Fast-moving

Prompt antibiotic treatment to prevent complications

• 10 days of antibiotics

  • Penicillin or erythromycin

Post-Streptococcal sequelae

1. Glomerulonephritis

• Kidney disease - infection and inflammation of glomeruli

2. Rheumatic fever

• Inflammatory disease that affects heart (damages heart valves), joints, skin, and brain

Diphtheria

Causative Agent = Corynebacterium diphtheriae

• Gram-positive, pleomorphic (rod or club shaped) bacteria

• Disease due to diphtheria toxin

  • Produce toxin due to lysogenic conversion

  • Toxins inhibit ribosome (protein synthesis) → cell death

• Symptoms

  • Mild sore throat, slight fever, fatigue

  • Neck swelling and formation of pseudo membrane (whitish membrane) on tonsils, throat or in nasal cavity

Transmission

• Air or fomites

Treatment

• Antibiotics to eliminate bacteria

  • Penicillin and erythromycin

• Antiserum to absorb toxin

• ~10% mortality even with treatment

Prevention

• Immunization with inactivated toxoid very effective

  • DTaP, Tdap

  • Booster every 7 years

Viral Infections of the Upper Respiratory System

Very common infections

• Average person in U.S. gets 2-5 per year

• Infections usually subside without treatment or permanent damage

• Can weaken defenses

  • Allow for more serious bacterial infections (secondary infections)

Common cold:

• Most common infectious disease in humans

• Accounts for more than half of upper respiratory infections

• Causative Agents: “cold viruses”

  • 30-50% caused by rhinoviruses

  • Only need a few virions to infect

• Symptoms:

  • Malaise, sore throat, runny nose, cough, hoarseness

  • Fever only with secondary bacterial infection

  • Symptoms gone within a week

• Spread by close contact with infected person or nasal secretions

• Prevention: Hand washing, keeping hands away from face

Bacterial Infections of the Lower Respiratory System

Less common, more serious complications

Pneumonia

• Fluid accumulation in lungs (pus and blood fills alveoli) → inflammatory response

• Can be deadly

• Causative agent: bacterial, viral, fungal

• Diagnosed by chest x-ray (white shadows)

Pneumococcal Pneumonia

Causative agent = Streptococcus pneumoniae

• Gram-positive, diplococcus (pneumococcus)

• Thick polysaccharides capsule responsible for virulence

Account for 1/3 of adult community-acquired pneumonia in U.S.

Kills about 1 out of 20 people who get it

Signs and Symptoms:

• Runny nose and upper respiratory congestion

• Then,

  • Cough with rust color sputum from blood

  • High fever and chill

  • Severe chest pain

    • Breathing becomes shallow and rapid

      • Cyanosis results - skin becomes dusky colored due to poor oxygenation

Antibiotic treatment

• Penicillin and erythromycin

• Drug resistant strains increasingly common → outbreaks

Prevention by vaccine

• Pneumococcal polysaccharide vaccine (PPSV23)

  • Protects against 23 types of pneumococcal strains

  • Recommended for people at greater risk

    • 65 years and older

    • The very young

    • with certain health problems (heart/lung disease)

    • With a weakened immune system

Klebsiella Pneumonia

Common nosocomial infection, especially in immunocompromised individuals

Causative agent = Klebsiella pneumoniae

• Encapsulated Gram-negative rod, mucoid colonies

• Normal microbiota of GI tract, mouth and throat

• Causes severe pneumonia → scars in lungs

  • Distinguished from pneumococcal pneumonia by repeated chills, production of bloody gelatinous sputum

  • 50% to 80% mortality in untreated patients

    • Patients die sooner than those with other types of pneumonia

  • Treatment with antibiotics, but strains becoming resistant

    • Those circulating in hospitals, and nursing homes

  • No vaccine available

Mycoplasmal Pneumonia

Causative agent: Mycoplasma pneumoniae

• Small, lacks cell wall which is why they’re pleomorphic, slow growth

• Small infecting dose, inhaled

  • Attaches to and interferes with function of cilia → inflammation in the lungs

  • inflammation leads to fluid accumulation and leads to pneumonia

Leading pneumonia of children and young adults

• Mild disease, aka “walking pneumoniae” or atypical pneumonia

• First symptoms: Sore throat, chills, fever, headache, muscle pain, fatigue

• Later symptoms: Dry cough and mucoid sputum

Treatment and Prevention:

• Antibiotics that do not target cell wall

  • No vaccine available *only one is for pneumocoocal pneumoniae

Pertussis (Whooping Cough)

Causative Agent = Bordetella pertussis

• Small, aerobic, encapsulated Gram-negative rod

• Spread from adult to children

• Attach to and destroy ciliated cells via pertussis toxin

  • Leads to increased mucus formation → decreased ciliary action

  • Cough - only mechanism for clearing secretions bcuz its hard for mucus covered cilia to move

• Highly contagious, spread via air droplets

• Symptoms

  • Paroxymal coughing – violent, uncontrollable coughing followed by characteristic “whoop”

• Exhaustion, vomiting and seizure may occur

• Death due to pneumonia from B. pertussis or secondary infections

• Pertussis in young children can be deadly

  • Often require intensive support care

• Treatment:

  • Erythromycin in the early stages

• Prevention

  • Vaccination

    • Injections at 6 weeks, 4, 6, and 18 months (DTaP)

    • Boosters required every 7 years (Tdap)

  • Recent outbreaks due to lapse in vaccination in adults bcuz they dont get their booster

    • then they get infected and spread it to young children

• Infants under one year old are at greatest risk for serious disease and death

Tuberculosis

Causative agent = Mycobacterium tuberculosis

• Strict aerobic, Gram-positive rod

• Slow growing (chronic disease)

• Acid-fast bacteria

  • Waxy cell wall (mycolic acids)

Primarily infects lungs

• Can spread and cause disease in other tissues (bones, kidneys, joints, central nervous system)

Signs/symptoms

• Fever with night sweats

• Progressive weight loss

• Chronic productive cough

  • Sputum often blood streaked

Once common; cases declined as living standards improved

1980’s – rise in cases due to AIDS epidemic and drug-resistant strains

• In homeless and HIV infected individuals

Airborne - Hard to contain

• 2024 Global statistics

  • TB - leading cause of death from a single infectious agent; top 10 causes of death

  • 10.7 million new cases

  • 1.23 million deaths (150 000 among people with HIV)

    • TB - leading killer of people with HIV in 2024

• MDR-TB remains a public health crisis

Epidemiology

• 13 million American infected

  • Highest among non-white, elderly, poor people

• Small infecting dose (Ten or less inhaled bacteria)

Tuberculin skin test

• Used to detect those infected

• Positive test does not indicate active disease

Treatment

• First-line antibiotic for active tuberculosis

  • Combination of rifampin (RIF), isoniazid (INH), pyrazinamide (PZA), and ethambutol (EMB) given for 2 months; then INH, RIF for another 4–7 months

• For MDR-TB

  • Treatment is longer (18-24 months)

  • Second-line drugs may be used

• XDR-TB (extensively drug-resistant TB): resists both first and many second-line drugs

  • New regimen of medications used

Prevention

• Vaccination

  • Bacillus of Calmette and Guérin (BCG)

    • Attenuated virus derived from Mycobacterium bovis

    • Gives partial immunity

  • Not given in United States

    • Interferes with TB test

  • Not safe in severely immunocompromised patients

Viral Infections of the Lower Respiratory System

Most are RNA viruses

• Infect more individuals, potential for serious outcomes

Influenza

Causative Agent = Influenza A virus

• Enveloped virus in Orthomyxoviridae family

• Single-stranded RNA genome in 8 segments

• Spikes in envelope

  • H spike – hemagglutinin

    • Attaches to receptors of host cell

  • N spikes – neuraminidase

    • Destroys host receptor and releases virion from host cell

Signs and symptoms

• Headache

• Fever

• Sore throat

• Muscle pain

• Dry cough

Subtypes based on H and N spikes

• H5N1: 1997 “avian flu”

• H1N1: 2009 “swine flu”

Pathogenesis

• Acquired through inhalation of respiratory droplets or from contaminated fomites

• Virus infects and replicates in ciliated respiratory epithelial cells

• Viruses leave host cell by budding

• Infected cells die and slough off

  • Destroy mucociliary escalator

Epidemiology

• Infects ~20% of humans annually; overall numbers of death is high

  • Most deaths due to secondary infections

• In the U.S, the flu can be a major public health burden

  • Epidemics occur every year

  • CDC estimates that influenza results in: deaths, hospitalizations, illnesses