Airborne infections Flashcards
What are some of the human respiratory tracts defence mechanisms?
Physical defences Filtration systems Only small particles will reach the alveoli (<5 micrometers) Mucocilary stream Coughing
How does the mucocilary system act as a defence?
Coats surface of respiratory tract right down to alveoli, binds any particulates as they enter the respiratory tract
What are the alveolar macrophages?
Primary defence of the lungs
What are the effector cells for alveolar macrophages?
Phagocytic
Microbicidal activities
What are the antigen presenting cells in alveolar macorphages?
Induction of acquired T-cell responses
What is the alveolar inflammatory (innate) response?
Influx of neutrophils (phagocytic and microbicidal) into the alveoli (diapedesis)
In response to chemotactic factors such as complement to combat the infection
What are the alveolar macrophages adaptive responses?
IgG and C- opsonins (promote phagocytosis)
Lymphoid tissue providing T and B cells for the immune response
What are the humoral defences of IgA antibodies?
Predominant class in the upper airways, more IgG in the lungs Mainly dimer form, S-IgA interacts with the mucin (secreted through epithelial) Prevents attachment of microorganisms neutralisation of toxins
What are other factors in humoral defences?
Lung surfactant- may enhance bactericidal activity of macrophage and complement
Lysozyme- digests bacterial peptidoglycan (enzyme)
Transferrin and lactoferrin- bind available iron
What bacterium causes diphtheria?
Corynebacterium diphtheriae
What is the structure of Corynebacterium diphtheriae?
Non-sporing (no spores, no dormant form of organism), aerobic Gram-positive bacillus
Where does Corynebacterium diphtheriae grow?
Doesn’t go further than the back of the throat
Grows in upper respiratory tract (usually throat)
Where does corynebacterium diphtheriae cause damage?
Extracellular
Does not invade the tissue
What shape are C. diphtheria?
Club shaped
What are the steps of pathogenesis?
Inflammation of the pharynx
Significant inflammatory response
Pseudo-membrane and toxins associated with deaths
Largely toxin mediated disease (diphtheria toxin)
What are the other factors in the cause of pathogenesis?
IgA protease- cleaves IgA
Pili for mucosal colonization
Consequence of inflammatory response- leathery pseudo-membrane of bacterial cells, dead inflammatory cells and fibrin
Cord factor (like M. tuberculosis) cell wall component
• Toxic for phagocytes
What is the diphtheria toxin responsible for?
Symptoms of diphtheria
Where is the diphtheria toxin?
Encoded on a bacteria phage
What carries the tox gene?
Lysogenic bacteriophage- destroys any cell it gets into, very potent, not a lot is required
What is ADP ribosyltransferase for?
EF2 (elongation factor 2)
o Involved in protein synthesis
o Transfers ADP-ribose from NAD to EF2
What are deaths in diphtheria due to?
A combination of partial suffocation and tissue-destroying effects of the toxin
How is diphtheria treated?
(Horse) antitoxin- neutralises toxin
Antibiotics- must be given early
Penicillin, erythromycin
What is the diphtheria vaccine?
Triple vaccine DTaP
Formalin-treated diphtheria toxin (toxoid) (D)
Ad tetanus toxoid (T) and pertussis acellular vaccine (aP)
Why must diphtheria vaccination continue?
Vaccination does not prevent the carriage and the organism persists in the community
