Pathogens and the host Flashcards
pathogenic bacteria
bacteria capable of causing disease.
signs and symptoms of clinical infection
- inflammation
- pain
- pyrexia
- tachycardia
- rigors
- increased white cell count
- increased C reactive protein (CRP)
pyrexia
high temp.
tachycardia
heart rate that exceeds the normal resting rate.
rigors
sudden feeling of cold, increased temperature, sweating and shivering
pathogen
organism that can cause disease.
commensal
organism which is part of the normal body flora.
requirements for pathogenicity
infectivity
virulence
infectivity
ability to become established
virulence
ability to cause harmful effects once established
methods to increase infectivity
- attachment
- acid resistance
virulence factors
- invasiveness
- toxin production
- evasion of immune system
invasiveness example: streptococcus pyogenes
- necrotising fasciitis
- cellulitis
- connective tissue breakdown
- fibrinolysis
types of toxins produced by pathogens
exotoxins
enterotoxins
endotoxins
exotoxins
released extracellularly by the micro-organism.
enterotoxin
act on the GI tract
endotoxin
structurally part of the gram negative cell wall
tetanus
caused by clostridium tetani, exotoxin released acts on nerve synapse and causes the inhibition of inhibitory neurotransmitter release.
tetanus treatment
debridement (removal of dead/infected tissue), antibiotics and antitoxin
cholera
causes by vibrio cholerae, colonises small intestine produces an enterotoxin which causes increase in cAMP levels, increases ion conc in small intestine which causes dehydration.
treatment of cholera
rehydration
superantigens
certain exotoxins of strep pyogenes and Staph aureus stimulate the division of T-cells in the absence of specific antigen. overwhelming cytokine production causes toxic shock
endotoxin action
caused by E. coli and other gram negative bacilli. induces uncontrolled host response, cytokine production, fevers, rigors hypotension, tachycardia, collapse
colonisation
the establishment of the pathogen at the appropriate portal of entry
latent infection
after the primary infection the virus lies dormant in host cells, viral DNA and RNA in host cells which is not expressed in large quantities.
asymptomatic infection
infected host is a carrier for the disease but does not show any symptoms.
infection
the invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce
innate immunity
non-specific immunity formed of skin, gastric acid. muco-ciliary escalator and phagocytic cells
phagocytic cells
- polymorphs eg. neutrophils, eosinophils, basophils (fight acute infection
- macrophages (fight chronic infection)
aquired immunity
specific response to antigen concerned, an immunological memory is creates.
has a humoral (antibody) and cellular (t-cell) response
IgM
involved in primary response
IgG
involved in secondary response
IgA
mucosal immunity
IgE
allergy and helminth infection
sites of viral entry
- conjunctiva (mucus membrane over eye)
- respiratory tract
- arthropod
- alimentary tract
- skin
- urinogenital tract
acute viral infection
short time where host is infected with virus then nothing after. localised to specific site of body or can develop viraemia which causes widespread infection of tissues.
examples of acute viral infections
influenza A virus
enterovirus
influenza A
virus infects cells of the respiratory tract, destruction of respiratory epithelium, fever caused by altered cytokine expression.
antigenic drift
minor changes in genes of a virus over time to generate antigenic variants.
antigenic shift
abrupt major changes in virus antigenic structure.
enterovirus infection
virus infects gut then can cause viraemia which allows it to spread to neural (causes paralysis) and non-neural tissue
examples of enterovirus infections
Poliomyelitis (poliovirus) Aseptic meningitis (many enteroviruses) Myocarditis (coxsackie B viruses) Pancreatitis (coxsackie B viruses) Respiratory infections (many enteroviruses)
virus induced tumours
virus infects cells and viral nucleic acid. this is incorporated into host genome causing change in cellular gene expression.
This can cause uncontrolled cell multiplication and tumour formation.
production of antibodies
antibodies produced by B-lymphocytes when specific epitope is recognised, this is aided by t helper cells (CD4 T cells)
antibody in infection
- Neutralises bacterial toxins
- Neutralises viruses in viraemic stage
- Prevents adherence of microorganisms
- Opsonises capsulate organisms
- Useful means of diagnosis (serology)
cell mediated immunity
CD4 Th1 helper cells activate macrophages to ingest and kill or contain pathogen.
humoral immunity
memory B-cells are retained after an infection so that they can rapidly divide when the infection reoccurs.
superantigens
Certain exotoxins of Strep pyogenes and Staph aureus
are able to stimulate division of T cells in the absence of specific antigen. Causes overwhelming cytokine production, causing “toxic shock”.
