Flashcards in Respiratory system Deck (119)
Mycobacteria and TB: mycobacterium TB facts
- 2-4 μ by 0.2-0.5 μ
- Obligate aerobe: well-aerated upper lobes
- Facultative intracellular parasite: usually macrophages - because it's made up of a lot of lipids so can grow inside the macrophages without being killed
- Slow generation time
M.bovis from cattle
Mycobacteria and TB: Where does TB most commonly affect?
Lungs - pulmonary TB but can also affect the lymph nodes, bones, joints and kidneys and it can cause meningitis
Mycobacteria and TB: How does TB spread and who is more likely to affect?
TB is most commonly spread in droplets being coughed or sneezed into the air
Frequent or close prolonged contact with an infected person is necessary
People with already weakened immune system
Mycobacteria and TB: Who are the at risk groups of TB?
Steroids, chemotherapy, transplants, elderly
Unhealthy, over-crowded conditions
Stay in high-rate country- S.E. Asia, sub-Saharan Africa, parts E.Europe
Those exposed to TB in youth
Children of parents from high-rate countries
Prisoners, drug addicts, alcoholics
Mycobacteria and TB: Where and how does primary TB start?
Droplet nuclei inhaled
Taken up by alveolar
macrophages – not
Droplet nuclei (c.5 μ) reach the alveoli where the infection begins
Granuloma in lung = Ghon focus
Enlarged lymph nodes + GF = Primary Complex
---> mild flu like symptoms
Mycobacteria and TB: how does secondary TB occur?
Reactivation of dormant mycobacteria when something happens to the T cells: impaired immune function
Reinfection in a person previously sensitised to mycobacterial antigens
- occurs months, years or decades after primary infection
- reactivation most commonly occurs at apex of lungs - highly oxygenated
Mycobacteria and TB: What is the mechanism of secondary TB?
- Caseous centres of tubercles liquefy
- Organisms grow very rapidly in this
- Large Ag load
- bronchi walls become necrotic and rupture
- cavity formation
- organisms spill into airways and spread to other areas of lung: highly infectious
- Primary lesions heal
- Ghon complex, Simon foci
Mycobacteria and TB: What is milliary TB?
rapid dissemination of th organism
Mycobacteria and TB: How do you classify a TB infection (not lung disease) LEARN
Tuberculin skin test positive
Chest X-ray normal
Sputum smears negative
Sputum culture negative
Not defined as a case of TB
Only 3-4% of those infected develop active disease upon initial infection, 5-10% within one year
Mycobacteria and TB: How do you classify a TB lung disease? LEARN
Tuberculin skin test positive
Lesion on chest X-ray
Sputum smear positive
Sputum culture positive
Defined as a case of TB
Mycobacteria and TB: What are the most common symptoms?
Cytokines (TNF, IL-3, GM-CSF)
Persistent cough, +/- sputum
Swollen glands (usually in the neck)
Sense of tiredness and being unwell
Coughing up blood
can't really diagnose from symptoms
Mycobacteria and TB: What is the standard recommended regimen?
Isoniazid, rifampicin, pyrazinamide and ethambutol
for two months followed by isoniazid and rifampicin for four months
Trying to treat without the organism becoming resistant to the antibiotic, that's why there is a standard regime
Mycobacteria and TB: Why is there a standard recommended regimen?
Prevent spread of MDR-TB
standardized drug regimens
directly observed treatment (DOT)
good supply of high quality drugs
isolation of infectious patients - negative pressure isolation room
Mycobacteria and TB: What role does vitamin D play in TB?
Vitamin D has role in activating macrophages to destroy mycobacteria
Often a vitamin D deficiency in ethnic populations in UK
Mycobacteria and TB: What is the timeline of treatment of TB?
Non-infectious after c. 2 weeks
Begin to feel better after 2-4 weeks
Treatment must continue for 6 months + - must prevent resistance developing
Longer treatment for TB meningitis or if TB is resistant
Mycobacteria and TB: What are the fatality rates?
Untreated TB - 40 to 60%
- 5 to 50%
- depending on nutrition; quality and availability of medical care; HIV status
Mycobacteria and TB: What is the BCG vaccine and how does it affect the skin test?
Protection restricted to childhood tuberculosis which is rarely infectious
No impact on HIV-related TB
Does not prevent infection – only disease
Invalidates tuberculin skin test
Therefore – targeted vaccination; effective for about 15 y
Mycobacteria and TB: what is the link between TB and HIV?
HIV / AIDS and TB are overlapping epidemics – “the unholy alliance”
- Worldwide 30-80% of AIDS patients get TB
HIV increases risk of acquiring TB
Destroys immune system
TB makes HIV worse
Increases replication rate of HIV
TB treatment slows down HIV and keeps patients alive to get HIV drugs
Mycobacteria and TB: What are the obstacles to TB control?
Lack of financial resources- half of all cases in China, Indonesia, India, Pakistan and Bangladesh
Social instability - e.g. Russia
- HIV/AIDS doubles the TB death rate
- 30 to 70% of TB cases in Africa are HIV positive
- reinfection in South Africa
Mycobacteria and TB: What do skin tests do?
Heaf, Tine, Mantoux
- ascertains infection rather than disease
- may be negative in severe TB or concomitant HIV, malnutrition, steroids
- may be positive with BCG or after exposure to environmental mycobacteria
Mycobacteria and TB: What are T- SPOT TB & QuantiFeron gold?
Blood tests to replace tuberculin tests
Detect reactive T cells - specific for mycobacterium TB, not for BCG
Specific for Mtb
Mycobacteria and TB: How is microscopy used to look at TB sputum?
Ziehl-Neelsen stain: Needs > 10,000 organism/ml at 100X lens
Rhodamine-Auramine is more sensitive
One-third of pulmonary TB (two-thirds extra-pulmonary) undiagnosed by microscopy
Mycobacteria and TB: How do you culture TB sputum?
Homogenise (Sputasol - breaks it down)
Decontaminate (4% NaOH Petroff) - kills all bacteria but the mycobacterium
4-6 weeks for visible colonies
(Liquid media; Kirchner’s)
Mycobacteria and TB: how does automatic culturing work?
- Fluorescent reaction quenched by O2
- Growth of mycobacteria lifts quenching and tubes fluoresce
- 10 days
another test - MPT64 - antigen ONLY given off by TB so this test is done afterwards
Mycobacteria and TB: Look at nucleic acid detection tests again -
MTB complex - rifampicin resistance genes
Mycobacteria and TB: how is typing carried out?
- Variable Number of Tandem Repeats
- Mycobacterial Interspersed Repetitive Units
- e.g. VNTR 84455 MIRU 244428223533
17 digit profile given - fingerprint of that organism so can track the infection
Respiratory viruses and atypical pathogens: Why are some viruses restricted to infecting certain areas?
expression of different types of cell expressed receptors.
Respiratory viruses and atypical pathogens: What are the types of infection? and the two types of invaders?
Surface: - local spread
- short incubation
e.g. common cold, Candida
Systemic: - spreads from mucosal site of entry to other site in the body
- returns to surface for final shedding stage
- longer incubation: weeks
- e.g. measles, mumps, rubella
Professional invaders:- infect healthy respiratory tract
Secondary invaders: - infect compromised tract
Respiratory viruses and atypical pathogens: What is Rhinitis and sinusitis?
The common cold
Caused by various viruses
Transmission by aerosol
Self-limiting (surface infections) and not systemic in healthy people
Identification usually not necessary unless clinical symptoms worsen- Involvement of LRT.
Molecular methods most common for ID, epidemiololgical info only
no vaccines - viruses change regularly and many of them cause the same symptoms