strep throat, scarlet fever, rheumatic fever
repeated streptococcal pharyngitis infections can lead to what chronic disease?
chronic rheumatic heart disease 1. rigidity of valves and/or thickening of chordae 2. leads to stenosis or insufficiency
what causes rheumatic fever?
molecular mimicry 1. host and s. pyogenes share antigenic determinants 2. M protein epitopes are similar to epitopes of human myosin 3. antibodies generated against M protein act on LAMININ (similar to myosin) → upregulate VCAM 4. T cell binds VCAM → inflammatory response → damage heart valve
are cultures useful for confirming rheumatic heart disease?
no 1. bacterium unlikely present 2. use serologic tests for antibodies against virulence factors a. ASO (streptolysin O) b. anti-DNase (DNases) c. anti-hyaluronidase
does treatment of strep affect the course of rheumatic fever?
no 1. immune complex responsible for rheumatic fever not affected by antibiotics 2. use steroids and NSAIDs for rheumatic fever
which virulence factor in s. pyogenes is most likely to cause severe systemic complications?
s. pyogenes w/ hyaluronic acid capsule 1. hyaluron is present in normal human cells 2. body sees it as self antigen → won't be phagocytosed → able to spread
what is unique about s. pyogenes that causes scarlet fever?
scarlet fever is only caused by s. pyogenes that has been infected w/ a bacteriophage
what streptolysin is responsible for s. pyogenes' β hemolysis?
streptolysin S
what is the main colonization site of s. pyogenes?
the oropharynx is the main colonization site of s. pyogenes
what is the primary symptom of scarlet fever?
1. diffuse erythemous rash: via SpeA, SpeB, SpeC, SpeF 2. develops 1-2 days after strep throat symptoms 3. starts on chest, spreads to extremities 4. spares mouth, soles, and palms 5. BEST SEEN ON PASTIA'S LINES (abdomen, skin folds) 6. desquamation after 5-7 days 7. strawberry tongue
what are characteristics of the strep test?
1. done in office 2. rapid 3. very specific, very low sensitivity (<90%)
how does strep pyogenes avoid phagocytosis?
1. hyaluronic acid capsule: interferes w/ phagocytosis 2. M protein: bind serum β-globulin factor H → degrades C3b 3. C5a peptidase: inactivates C5a (chemokine), inhibits abscess formation
what are diseases caused by s. pyogenes?
1. streptococcal pharyngitis a. scarlet fever b. rheumatic fever 2. impetigo 3. cellulitis 4. necrotizing fasciitis
what bacteria is the cause of strep throat?
1. streptococcus pyogenes
diagnostic tests for s. pyogenes detect antibodies to what virulence factors?
1. streptolysin O 2. DNAse B 3. streptokinase
what is the function of streptokinase A & B?
1. virulence factor of S. pyogenes 2. degrades blood clots and fibrin deposits 3. facilitates spread of bacterium
what is the function of DNase A, B, C, & D?
1. virulence factor of S. pyogenes 2. depolymerize free DNA in pus 3. reduces viscosity & facilitates spread of bacteria
what is the function of streptolysin S & O?
1. virulence factor of S. pyogenes 2. lyse leukocytes, erythrocytes, and platelets 3. streptolysin S responsible for β hemolysis
how does strep pyogenes adhere and invade host cells?
1. weak lipoteichoic acid and FA binding sites on fibronectin and epithelial cells 2. M and F protein interact w/ receptors → firm attachment 3. M and F protein stimulate phagocytosis of s. pyogenes → sustained infection
what lab values are typically elevated in rheumatic fever?
1. ↑CK-MB 2. ↑↑Troponin I
how is s. pyogenes transmitted?
s. pyogenes is transmitted via droplet infection
how is rheumatic fever treated?
1. anti-inflammatory agents 2. steroid for carditis 3. aspirin and prednisone
what antibodies are tested for confirming rheumatic heart disease?
1. ASO (streptolysin O) 2. anti-DNase (DNases) 3. anti-hyaluronidase
what are prophylactic treatments for rheumatic fever?
1. IM benzathine pencillin monthly
what are the virulence factors of s. pyogenes?
1. M protein: adhesion, degrades C3b 2. C5a peptidase: inactivates C5a (chemokine), inhibits abscess formation 3. streptolysin S & O: lyse leukocytes 4. streptokinase A & B: degrade blood clots and fibrin deposits → bacterial spread 5. DNAse A, B, C, D: depolymerize DNA in pus → ↓viscosity, facilitates spread 6. SpeA, SpeB, SpeC, SpeF: exotoxins, superantigens
what is poststreptococcal glmoerulonephritis (PSGN)?
1. acute glomerulonephritis following infection w/ nephritogenic strain of s. pyogenes 2. symptoms: hematuria, hypertension, renal failure 3. latent 7-14 days following pharyngitis 4. latent 14-21 days following impetigo 5. ages 2-40 y/o
what is the main virulence factor of strep pyogenes?
M protein 1. 2 chains in an α-helix 2. anchored in membrane 3. varied extracellular AA sequence = antigenic variability 4. rheumatic heart disease
what is responsible for the rash in scarlet fever?
s. pyogenes exotoxins SpeA, SpeB, SpeC, SpeF 1. superantigens: stimulate secretion of inflammatory cytokines
