Infection Flashcards
what is pathogenicity
capacity for a microorganism to cause infection
what factors are needed for pathogenicity
transmissible, establish in the host, harmful effects, persistent
what are virulence factors
encoded by virulence genes, allow the micro-organism to be harmful by: ]facilitating adhesion or invasion
having toxic effects
interfere with hot defences
what is infectivity and what does it require
ability for a MO to establish itself in a host
requires ligand receptor interactions
what is an LD50 or ID50
doses that will cause death or infection in 50% of host exposures
what are the parts in the circle of infection
pathogenic organism reservoir exit transmission entry susceptible host pathogenic organism etc
what are the 5 steps in the impact of infection on the host
inflammation
abscess formation
excessive host response to endotoxin
granuloma formation
why do we have inflammation in infection
response to invasion/tissue damage caused by an infective organism
why is inflammation good and bad
protective functions but also reduces endothelial barrier function and can from abscess
what is an abscess
enclosed collection of pus ( made up of dead WBC’s, exudate, tissue and MO)
what are the clinical features of abscess formation
fluid filled fluctuant mass surround by inflammation with symptoms of infection
what are common causes of superficial abscess formation
s. aureus
s. pyogenes
what are endotoxins
part of the outer membrane of gram negative cells and are released from them upon their death
what is the active component in an endotoxin
LPS
liposaccharides - bind to receptors on phagocytes and lymphocytes
what are some host responses to endotoxin infection
uncontrolled cytokine releases - fever, riggers, hypotension, tachycardia
activation of clotting cascade (DIC and depletion of clotting factors)
activation of complement
what is neisseria meningitidis
endotoxin mediated increase in vascular permeability causes loss of protein fluid and plasma into tissues with pathological compensatory vasoconstriction which causes gangrenous appearance of extremities
what is botulism
clostridium botulinum
contained food/wounds/GI colonisation
irreversibly bind to presynoatic vesicles and stabilises them so no muscle contraction - flaccid paralysis = respiratory failure
what is tetanus
dirty or trivial wounds - tetanospasmin inhibits relates of inhibitory neurotransmitters = rigid paralysis
opisthotonos, sardonic smile, death from rest failure
what is a granuloma
collection of inflammatory cells due to persistence of non-degradable product and active cell mediated hypersensitivity
on examination of a granuloma what is present
nodule - pulmonary, hepatic etc
tissue necrosis - caseating
how does TB from granuloma
primary TB characterised by ranke/ghon complex - solitary granuloma with hilar granulomatous lymphadenopathy
reactivation - inflammation
extrapulmoanry TB - manifests in the bone liver kidneys etc
what are two cases of granuloma other than TB
schistosomiasis - helminths
viral infections
