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
How many deaths and infection are caused by tuberculosis?
9m new cases p.a. with approx. 1.7m deaths and 1/3 of population infected in some countries
Why are there so many tuberculosis related deaths?
HIV african countries means they have more vulnerable immune systems
Continual antibiotic resistance to TB
What is the bacterium that causes tuberculosis?
Mycobacterium tuberculosis
What is the structure of mycobacterium tuberculosis?
Slow growing, non-sporing, aerobic, Gram-positive bacillus
How is Mycobacterium tuberculosis acquired?
Inhalation, tubercle bacilli survive for long periods in air or dust
From milk, from cases of bovine TB (mycobacterium bovis), before pasteurisation
What is the primary pathogenesis of TB?
Lung disease but may affect any organ including a cause of meningitis
What is the damage of TB due to?
Not the toxin but the host immune response trying to combat this persistent organism
What are the steps leading to pathogenesis of TB causing death?
Inhalation of bacteria
Bacteria reached lungs; enter macrophages
Bacteria reproduce in macrophages
Lesion begins to form (caseuous necrosis)
Lesion liquifies
Spread to blood, organs
Death
What antibiotics are given to treat TB?
Prolonged treatment (6-18 months) with combinations of isoniazid, rifampicin and other drugs)
What is the problem with antibiotics for TB?
Emergence of resistant strains
What are some examples of the resistant strains of TB?
MDR-TB (mutli-drug resistant)
o Resistant to at least isoniazid and rifampicin, the two most powerful first-line drugs
XDR-TB (extensively drug resistant)
o As above, plus resistance to some second-line drugs
What vaccine is used for TB?
Live attenuated vaccine
BCG (Bacille Calmette-Guerin)
When was the first TB vaccine used in humans?
1921
How many people have the TB vaccine?
3 billion to date
What percentage of children are vaccinated for TB?
80%
Why does the TB vaccine’s efficacy range from 80%-0%?
Vaccine batch variability
Human genetic factors
Pre-exposure to mycobacteria in environment
Why has there been a resurgence in number of TB cases?
Neglect of health care programmes
Link with homelessness, drug abuse, migration of populations
Rapid international travel
Link with AIDS (HIV destroys CD4 cells)
