BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 1
RESPIRATORY TRACT
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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  absenteeism
 Upper - usually mild & self-limiting
 Lower - can be severe & life-threatening
 in children
 bacterial in adults
Upper Respiratory Tract Infections
itis = inflammation - surface infections
1. Rhinitis = cold
 100% viral (see Table 18.4)
 Rhinovirus and Coronaviruses - 50%
 115 different Rhinoviruses all w/ different surface antigens
 Other viruses (Parainfluenza, Enterovirus, RSV, etc)
 transmission via aerosol and by contaminated hands
 bind to and infect ciliated epithelial cells of nose
 incubation is 1-3 days
 damage to epithelial cells  mild inflammation, release of
inflammatory mediators  abundant mucus
 diagnosed by clinical signs & symptoms (burning sensation in
nose/throat, followed by sneezing, runny nose, fatigue, malaise. Sore
throat and cough generally due to post nasal drip. No or low fever)
 treatment is symptomatic
 control – interferon, sIgA, and IgG - immunity is short-lived
BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 2
2. Pharyngitis (= sore throat) and tonsilitis
 infected mucosa or inflammation of lymphoid tissue
 70% viral – symptoms often include rhinorrhea, conjunctivitis,
malaise or fatigue, hoarseness, and low-grade fever
 Rhinovirus, Coronavirus, Adenovirus, etc, see Table 18.5
 CMV -clinically silent in URT esp. in infant/child – can spread
from blood to placenta and infect fetus; second only to Down’s as
a cause of mental retardation
 EBV -2 peaks 1-6 years and 14-20 years (infectious mononucleosis
– fever, sore throat, petechiae on hard palate, lymphadenopathy
and splenomegaly, with anorexia and lethargy. Symptoms due to
release of cytokines. Plyclonal activation of B cells; WBC dif
shows at least 10% atypical lymphocytes) EBV infections can reactivate, see Fig. 18.6.
 30% bacterial – usually no rhinorrhea, cough, or conjunctivitis
 S. pyogenes (age 5-15), onset is abrupt, acute - chills, headache,
severe sore throat, lymph nodes swell, tonsils tender w/ white, pusfilled lesions, high fever, no cough, no nasal discharge
 N. gonorrhoeae – in sexually active
 C. diphtheria – rare in U.S.
3. Otitis media and sinusitis = ear and sinus
 ear infections are second most common infection of childhood (after
colds) and most common cause of visits to pediatricians
 50% viral
 respiratory syncytial virus (RSV), influenza, parainfluenza,
rhinovirus, adenovirus
 50% bacteria - secondary invaders
 S. pneumoniae, Haemophilus influenzae, Moraxella
4. Epiglottitis
 H. influenzae type B (vaccination = Hib)
 Severe inflammation with edema  life-threatening respiratory
obstruction
BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 3
Lower Respiratory Tract Infections
1. Laryngitis and tracheitis
 Viruses (symptoms – hoarseness, burning retrosternal pain)
 Parainfluenza virus – croup (dry cough and inspiratory stridor)
 RSV, Influenza virus, Adenovirus
 Bacteria
 GAS, H. influenzae, S. aureus
 C. diphtheria - life threatening, rare in U.S. due to vaccination (DaPT)
2. 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 ADPribosylase, disrupts signal transduction in affected cell - prod
massive amts mucoid secretions
2. Adenylate cyclase toxin - enters neutrophils & causes them to incr.
cAMP - inhibits chemotaxis, phagocytosis, & killing
3. Tracheal cytotoxin - 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 - DaPT
 Rate of infection in unvaccinated exposed - 90-95%; Mortality - up to 14%
BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 4
3. 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
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
BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 5
5. 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
6. 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
BIO 580 Medical Microbiology Unit 3 Respiratory Tract Infections 6
 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
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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
7. Chronic Infections of the lungs
 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 jiroveci (formerally P. carinii) - pneumocystis
pneumonia
8. Cystic fibrosis
 very viscous bronchiol secretions leads to fluid stasis in the lungs &
infections w/ P. aeruginosa (S. aureus, H. influenzae, B. cepacia)