Infectious Aetiologies of Heart (Bacterial + Viral) Flashcards
what is the pathogenesis of infective endocarditis
need two things to happen:
- endothelial damage to valve (trauma, turbulence, metabolic change)
- mucous membrane trauma
platelets + fibrin aggregates try to repair the damage –> non-bacterial thrombotic vegetation (NBTV) forms and bacteria colonize and stick to this
- bactiera multiply –> becuase of fibrin deposition the bacteria is protected by neutrophil destruction
- bacteremia: constantly shed from vegetation –> positive blood cultures as vegetation gets larger –> embolize and break off and go to vital organs (brain –> stroke)
- heart valve becomes dysfunctional and destroyed
what is acute endocarditis
major pathogens
rapid course and onset
what is chronic endocarditis
(sub-acute)
less virulent pathogens
indolent course and onset
what is seen in endocarditis
- bacteria in blood and bacteremia continuous
- cardiac pre-disposition often –> congential damage/diseased valves –> subvalvular aortic stenosis –> mitral and aortic most affected
- new heart murmur
- fatal if not treated (antibiotics) or valve replacement in humans
what valve is this and identify the anatomy
the valve leaflets are smooth
what is MSCRAMM
microbial surface components recognizing adhesive matrix molecules
adhesin proteins mediate the initial attachment of bacteria to host tissue
fibronectin binding proteins of staphylococci (trauma from skin) and streptococci (mouth or gut)
list the steps that lead to bacterial deposition on the mitral valve
- endothelial injury
- platelet deposition
- microbials with MSCRAMMs –> bacterial adhesion to platelet fibronectin and fibrin matrix
- adhesion and incorperation of microbials into vegetation –> aggregates that build up on smooth valve and interfere with the mechanical function of the valve (heart murmur)
- vegetative lesion, ruptured chordea tendinae
what are the common bacterial causes of IE in dogs
>50% of cases caused by streptococci and coagulase positive staphylococci (staphylococcus pseudointermedius adn staph. aureus)
streptococci originate in mouth or gut
rarely due to gram negatives
bartonella
fungi rare in dogs and cats
what bacteria cause endocarditis in cattle
Streptococcus bovis
arcanobacteria (trueperella)
what bacteria cause endocarditis in pigs
erysipelothrix
what is the pathogenesis of endocarditis
- normal vascular endothelium resistant to microbial infection and few potentially at risk actually develop infective endocarditis
- since low-grade bacteremia occurs freq. a defence mechanism must exist that can eradicate microbes adherent to vegetation
- plalelets play a pivotal role in the antimicrobial host defence mechanism (thrombocidins)
- damage to the endothelial surface of the heart or blood vessel induces platelet and fibrin deposition, producing a sterile thrombotic vegetation
- infective endocarditis is initiated by binding of microbes, discharged in the general circulation from a peripheral site to these vegetations
- these microbes become encased further in depositions of platelets and fibrin and multiply
- extremely high concentrations of bacteria in the vegetation (10^9-10^11/gram tissue)
- hinders antibiotic penetration
- organisms may stop multiplying –> making them less susceptible to beta lactams (works on cell wall)
- bacterial enzymes destroy valve tissue (holes), rupture chordae tendinae and produce aortic root abscess
what are jet lesions
endocarditis is classically associated with jet lesions where blood flowing from ahigh pressure area through an orifice to an area of lower pressure produces a high velocity jet
vegetations are usually found in lower pressure area (atrial surface of mitral valve or the ventricular surface of the aortic valve)
what are the four basic processes once a vegetation is established
- bacteremia
- local tissue destruction
- embolization
- formation of circulating immune complexes
what pathology is shown here
emboli from aortic endocarditis causing infarcts in various organs
what are the pathogenesis of clinical signs of IE (9)
- valvular insufficiency and congestive heart failure
- bacteremia
- septic embolization and organ infarction
- metastatic infection and myocarditis
- immunopathologic sequelae and immune complex deposition
- glomerulonephritis
- uveitis
- polyarthritis
- meningitis
how is IE diagnosed (without echocardiogram, with echogardiogram, clinical findings)
without echocardiogram all criteria should be met:
- murmur of recent onset
- positive blood culture results (preferably with more than one of the same microbe)
- clinical findings and laboratory data consistent with bacteremia and endocarditis
with echocardiogram:
-aortic or mitral valve
supportive clinical findings:
- signalment
- murmur of recent onset
- weak or hyperdynamic pulse
- fever
- limb edema
- joint swelling
- lameness
- limb ischemia
- limber hyperesthesia
- inflammatory leukogram
- positive blood culture
what is the suggestive criteria for IE diagnosis
how is bacteremia identified
blood cultures
at least 3 cultures should be obtained from seperate sites within 24 hours
what class of antibiotics are used to treat
bactericidal
need to sterilize the vegetation
what is myocarditis
inflammation of heart muscle
what is the cause of myocarditis
infectious myocarditis in dogs and cats usually results from hematogenous spread of microorganisms to the myocardium or extension of endocarditis lesions to myocardium
viruses, bacteria, protozoa, fungi may be involed
some organisms have tropism for the myocardium
rare in cats
what are the bacterial, viral causes for myocarditis in dogs
canine distemper virus
canine parvo virus
borrelia burgdorferi
rickettsia rickettsii
what are the causes of myocarditis in cattle
clostridium chauvoei
listeria
what are the causes of myocarditis in pigs
encephalomyelitis virus
porcine circovirus 2
what are the causes of myocarditis in poultry
what are the causes of myocarditis in cats
bartonella
what causes pericarditis
infectious pericarditis may result from direct inoculation of organisms into pericardium (penetrating wounds)
extension of infection from adjacent organs such as pleural space or lungs
hematogenous dissemination of viral, bacteria, fungal pathogens to the pericardium
how is pericarditis diagnosed
sample pericardial fluid for bacterial culture/viral PCR, blood culture for bacteria
what are the bacterial, viruses that cause of pericarditis
what is immune complex glomerulonephritis
protein losing nephropathy
immune complex deposition on basement membrane –> antigen antibody reaction activates complement pathway –> damage to glomerular basement membrane
damage sufficient to allow albumin loss –> protein in urine
how long is antibiotics given
until its bettwe
6 weeks +++ (8-12)
enfrofloxacin/amoxicillin-clavulanate
what are acute phase proteins
part of innate immune system
raised in inflammation
most sensitive blood test available for detecting inflammation –> much more than WBC
go down as animal gets better
