RESPIRATORY TRACT

  • nose to alveoli
  • continuous operation is essential
  • constantly exposed to air & microbes
  • divided into 2 regions : upper & lower

Generalizations

·        Many cause local infections, some may spread systemically

·        Professional invaders - normal healthy host, specific attachment mechanisms, specific evasion tactics

·        Secondary invaders - impaired host

·        Most common infections seen by doctors

·        High morbidity à absenteeism

·        Upper - usually mild & self-limiting

·        Lower - can be severe & life-threatening

·        viral in children

·        bacterial in adults

Upper Respiratory Tract Infections

Clinical Syndromes

itis = inflammation - surface infections

1. Rhinitis = cold

  • excess mucus
  • viruses - rhinovirus + coronavirus

·        Rhinovirus

·        ½ of all colds

·        grow best at 33-34ºC

·        over 100 different Rhinoviruses all w/ different surface antigens

·        natural immunity is short-lived

·        Coronavirus

·        2nd most common cause of cold

  • spread via surface secretions
  • damage to epithelial cells à inflammation
  • diagnosed by clinical signs & symptoms
  • treatment is symptomatic

 

2. Pharyngitis = sore throat

·        infected mucosa or inflammation of lymphoid tissue

·        70% viral

·        Adenovirus

·        EBV

·        Herpes

·        Coxsackie A

·        30% bacterial

·        S. pyogenes (age 5-15), onset is abrupt, acute - chills, headache, severe sore throat, lymph nodes swell, tonsils tender w/ white, pus-filled lesions, high fever, no cough, no nasal discharge

·        C. diphtheria

·        H. influenzae type B

·        N. gonorrhoeae

3. Otitis media and sinusitis = ear and sinus

·        50% viral

·        mumps

·        respiratory syncytial virus (RSV)

·        50% bacteria - secondary invaders

·        S. pneumoniae

·        H. influenzae - brain

 

4. Epiglottitis

·        H. influenzae type B

·        life-threatening respiratory obstruction

 

5. Laryngitis and tracheitis

·        viruses

·        Parainfluenza virus - croup

·        RSV

·        Influenzae

·        Bacteria

·        C. diphtheria - life threatening

 

Lower Respiratory Tract Infections

 

1. Whooping cough

·        Org - Bordetella pertussis (GNR, ox +, obligate aerobe)

·        Humans are sole reservoir

·        Highly contagious

·        Transmission - person - person airborne droplets

·        Colonization - attach to ciliated mucosa in trachea using fimbriae & hemagglutinin also spreads to bronchi

·        Several toxic factors -affect inflammation or damage ciliated epithelium

1. pertussis toxin - A-B structure exotoxin; A unit is an ADP-ribosylase that disrupts signal transduction in affected cell - prod massive amts mucoid secretions

2. Adenylate cyclase toxin - enters neutrophils & causes them to ↑cAMP - inhibits chemotaxis, phagocytosis, & killing

3. Tracheal toxin - kills tracheal epithelial cells

4. Endotoxin

·        Incubation - 1-3 weeks

·        Pathology - ciliated epithelium of trachea becomes covered w/ massive purulent exudate

·        Presentation

early - runny nose, sneezing, fever, mild dry cough

week later - mucus & bact fill lower trachea, cough becomes paroxysmal - violent coughing fits, 5-20X w/ no breath in btwn - as air rushes back in - whoop

also vomiting, epistaxis, periorbital edema, conjunctival hemorrhage

·        Complications - CNS anoxia, secondary pneumonia

·        Immunization - DPT

·        Rate of infection in unvaccinated exposed - 90-95%

·        Mortality - up to 14%

 

2. Acute bronchitis - Inflammation of the tracheal/bronchial tree assoc w/ infection

·        Orgs

·        Professional pathogens; Viruses (rhino-, corona-, adeno-, influenzae,) and Mycoplasma pneumoniae

·        Secondary invaders - S. pneumoniae, H. influenzae

·        Presentation - cough - treatment is symptomatic - antibiotics? usually recommended

 

3. Bronchiolitis

·        children less than 2

·        swollen by inflammation, passage of air is restricted

·        necrosis of epithelial cells lining the bronchioles

·        Orgs

·        75% RSV

·        Respiratory Syncytial Virus - paramyxovirus (RNA), enveloped

·        Most common cause of fatal bronchiolitis & pneumonia in infants (1/100 hospital) - humans only reservoir

·        Transmission - resp. droplets to hands

·        Colonization - nasopharynx - surface spikes are fusion proteins that fuse host cells to cause "syncytia", then virus invades LRT by surface spread in secretions

·        Incubation 4-5 days

·        Immunopathology - maternal Ab in infant react w/ virus Ag, liberate histamine & other inflammatory mediators

·        Presentation - cough, rapid respiration, cyanosis

·        25% other viruses

 

4. Influenza = the Flu

·        Org - Influenzavirus types A, B, C; A - segmented RNA, 3 major HA types, 2 major NA types; antigenic epitopes change from yr-yr (antigenic drift & shift)

·        Transmission - person - person small airborne droplets

·        Colonization - attaches via HA to sialic acid receptors on ciliated epithelium of trachea/bronchi, RME

·        Incubation - 1-3 days

·        Pathology - impair mucociliary clearance, tracheobronchitis, bronchospasms; cytokines released from damaged cells & WBC may symptoms

·        Presentation - fever 102-104, chills, severe headache w/ retro-orbital pain, muscular aches (esp backache), dry cough, weakness (prostration).

·        Most cases resolve 1-2 wks

·        Complications - 1º influenza pneumonia (1% of cases but 30% fatality, pregnant women ↑ risk), 2º bacterial pneumonia (H. influenzae, S. pneumonia, S. aureus, S. pyogenes)

·        Epidemics are indicated by the number of unexpected deaths due to influenza, when # exceeds 10,000-50,000 = epidemic

 

5. Pneumonia

·        4,000,000 people/yr

·        Most common cause of infection related death in the US

·        6th leading cause of death

·        wide range of microbes

·        Transmission - inhalation or aspiration

·        Colonization - attach to resp epithelium

·        Pathology - respiratory distress from the interference of gas exchange in lungs, systemic effects

·        Orgs

·        children - viral or bacteria secondary to viruses

·        adults - bacterial, kind depends on risk factors, age, other diseases - in hospitals GN

 

·        Bacterial - acute onset, high fever

·        Typical - classic bacteria of acute, community-acquired - S. pneumoniae (25-60%), H. influenzae (5-15%), others - S. aureus, Klebsiella, E. coli, Pseudomonas

·        Atypical - M. pneumoniae, Chlamydia pneumoniae, Legionella pneumophila, Coxiella burnetii

·        Chest exam

·        rales (abnormal crackles)

·        evidence of consolidation

·        chest x-ray

 

·        Viral

·        Transmission - inhaled or from blood

·        Colonization - attach specifically

·        Orgs

·        RSV - children

·        Parainfluenza virus types 1 & 2 – children; hemagglutinin & neuraminidase & fusion proteins

·        Adenovirus - 41 types; 5% of acute resp. illness

·        Influenzavirus

 

6. Chronic Infections of the lungs

·        Orgs

·        Tuberculosis - review

·        Fungi

·        Aspergillus fumigatus – aspergillosis - Predisposing condition - asthma, pre-existing lung cavities, chronic pulmonary disorders - fungal ball aspergilloma doesn’t invade but in immunosuppressed - invade lungs to produce disseminated disease

·        Histoplasma capsulatum - histoplasmosis

·        Coccidiodes immitis - San Joaquin Valley Fever

·        Blastomyces dermititidis - blastomycosis

·        Pneumocystis carinii - pneumocystis pneumonia

 

7. Cystic fibrosis

·        very viscous bronchiol secretions leads to fluid stasis in the lungs & infections

·        Orgs P. aeruginosa (S. aureus, H. influenzae, B. cepacia)