Respiratory infections Chapter 23; pp561-596
Upper vs. lower respiratory tract - Fig23-1, p 563
normal flora of upper = table 23-1, p 564 (lower should be free)
Important defense mechanism = Mucociliary escalator
1) Streptococcal Pharyngitis (upper respiratory tract), rheumatic fever (Table
23-3 p569)
Streptococcus pyogenes (group A, ß-hemolytic) gram (+) coccus
(Strep Throat)
- Lancefield grouping - Carbohydrate on cell wall =
Fig 23-3, p 566
- virulence = adheres to throat epithelial by M protein
(Table 23-2, p566)
- symptoms = fever, inflammation of throat, may lead to otitis
media, glomerulonephritis
- scarlet fever = exotoxin encoded by lysogenic phage; results in
a rash
- rheumatic fever = inflammatory reaction in heart (autoimmune
reaction) (Fig 23-4, p567)
- treated with penicillin, erythromycin
- diagnosis = rapid strep test
2) Cold = most common respiratory tract infection (upper) Table
23-5 p574
- usually no fever, no cough initially
- Rhinovirus = RNA virus, no envelope; causes about 30-50% of
colds
- > 100 different serotypes
- generally spread by contact, to some extent by airborne
transmission
- cold may lead to secondary bacterial infections
3) Influenza (flu) (Table 23-11, p588))
- enveloped, segmented RNA virus Fig 23-21 p586
- contains hemagglutinin and neuraminidase spikes
- virus adheres to and infects respiratory epithelium via spikes
- symptoms = chills, fever, body aches, sore throat, cough (3-5
days)
- can lead to secondary bacterial infections e.g. pneumonia
caused by Streptococcus pneumoniae, Staphylococcus aureus
- can be treated with amantadine
- 3 types of flu virus = A, B, C; A = most severe
- influenza virus can change antigens on its surface (thru
mutations, recombination) Fig 23-22, p 587 = person no longer
immune
- antigenic drift = minor changes due to mutations, may result in
epidemics (every 2-4 years)
- antigenic shift = major changes due to recombination events,
may result in pandemics (approx. every 10 years)
- vaccines available
- may lead to Reye’s syndrome = swelling of brain, fatty
degeneration of liver; 25% fatal, others left retarded.
- some association with salicylates (aspirin)
4) Pneumonia (bacterial) lower respiratory tract (Table 23-7,
p579)
- may be caused by: Streptococcus pneumoniae, Klebsiella
pneumoniae, Staphylococcus aureus, Mycoplasma pneumoniae,
Hemophilus influenzae
Legionella pneumophila
- Streptococcus pneumoniae = major cause = pneumococcal pneumonia
- gram (+); chains or pairs (hence older name of diplococcus
pneumonia)
- virulence factor = capsule (S strains) resists phagocytosis
- symptoms = fever, chills, cough
- identified by Quellung reaction following positive X-ray
- treatment = penicillin, erythromycin
- vaccine is available to 23 common serotypes
5) Tuberculosis (consumption) lower respiratory tract (Table 23-9
p584)
- Mycobacterium tuberculosis (mycolic acids present = acid fast
stain)
- virulence = not destroyed after phagocytosis, multiply in
macrophages
- can cause swelling in lung = tubercles which calcify into
nodules
- can be chronic
- detected with skin test (Mantoux test), x-rays
- treated with isoniazid and rifampin, ethambutol
- symptoms = fever, fatigue, cough
- control = isolate infected persons
6) Histoplasmosis = systemic mycoses (Histoplasma capsulatum )
Table23-15 p593
- common in soil enriched by bird feces esp. chicken and turkey
- primarily a pulmonary disease
- symptoms = cough, fever, joint pain
- may be misdiagnosed as influenza
- may be chronic and resemble tuberculosis
- may be asymptomatic
- treatment = amphotericin B
- transmission = inhalation of spores
- distribution Fig 23-27, p593
7) Legionnaire’s disease (Legionellosis) lower respiratory
tract Table 23-10 p585
- pneumonia like symptoms
- caused by Legionella pneumophila = gram (-) rod
- facultative intracellular parasite
- not very contagious - spread via inhalation of aerosols
- virulence = infects monocytes and grows there
- treatment = erythromycin and rifampin
- control = elimination of sources (air conditioning cooling
towers)
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