Tuberculosis Flashcards
what is M. tuberculosis?
- a complex causative agent of TB
- rod shaped gram positive bacilli
- acid fast characteristics (resist acidic dyes)
- slow growing members of genus
How is TB spread?
-spitting, coughing sneezing
how many people who are infected individuals actually end up with the disease?
around 50%
which age group and ethnicity is most likely to get TB?
25-34
white (in the UK)
what are the majority of TB cases in the UK due to?
re-activated disease in individuals previously entering the country with latent TB infection
what is LTBI?
Latent tuberculosis infection (LTBI) is a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens without evidence of clinically manifested active TB. Someone has latent TB if they are infected with the TB bacteria but do not have signs of active TB disease and do not feel ill. However, they can develop active TB disease in the future.
what are the hosts possible immune responses (from most effective to least)?
healthy contact, lymph nodes, localised extrapulmonary, pulmonary localised, pulmonary widespread, meningeal, miliary
How is TB diagnosed?
- history and examination
- simple blood testing
- radiology/imaging
- microbiology and histology
How do you treat active drug sensitive TB?
for 2 months: Rifampicin, isoniazid, pyrazinamide, ethambutol
for a further 4 months: rifampicin and isoniazid
How do you treat latent drug sensitive TB?
2 months; rifampicin, isoniazid
or
isoniazid for 6 months
Describe the immune response to TB.
- initial intracellular primary niche is macrophages
1-macrophages, dendritic cells and neutrophils phagocytose infected cells
2- immune recognition and innate effector mechanisms
3-(slow) onset of Th-1 biased adaptive immunity
4- enhanced effector mechanisms (military, meningeal, pulmonary (widespread and localised), localised extrapulmonary, lymph nodes and healthy contact)
who has an increased risk of TB?
individuals with defective CMI (cell mediated Th-1 immunity) e.g HIV, children, chronic renal failure, those on corticosteroids or immunosuppressant therapy etc.
- also lifestyle factors e.g alcohol/ drug missuse, homless or in prison
- genetic susceptibility
what is the vaccine for TB?
BCG
how can latent TB be detected?
using highly sensitive T cell assays which interact with ESAT-6 and CFP10 targets in TB T-cells
what are the four main mycobacterial species collectively termed mycobacterium tuberculosis complex?
- mycobacterium tuberculosis
- mycobacterium bovis
- mycobacterium africanum
- mycobacterium microti
what happens in the first 4-6 weeks of TB infection?
route 1 = inhalation of bacilli > innate immune reponse clears bacilli before reaching lymph node, no infection.
route 2 = initial inhalation > formation of ghon complex leads to granuloma inflammation > initial containment of ing=fection within granuloma (LATENT TB) > reactivation as immune system fails to kill TB
route 3 = after inflammation of granulomas > inability to control organism >primary active TB
what are features of latent TB?
- bacilli present in Ghon focus
- sputum smear and culture negative
- tuberculin skin test usually positive
- chest X-ray normal (small calcified Ghon focus frequently visible)
- asymptomatic
- not infectious
what are features of active TB?
- bacilli present in tissues or secretions
- sputum commonly smear and cuylture positive
- tuberculin skin test usually positive
- chest X-ray shows signs of consolidation/ cavitation/ effusion in pulmonary disease and thickening or widening of mediastinum
- symptomatic
- infectious
what are symptoms of TB?
- night sweats , fevers, weight loss and cough
- occasionally haemoptysis
- hoarse voice
- pleuritic pain
what is the second most common site of TB after pulmonary TB?
lymph node TB
- usually presents as a firm, non-tender enlargement of a cervical or supraclavicular node.
what is miliary TB?
- occurs through haematogenous spread of bacilli to multiple sites including CNS
- systematic upset with findings in multiple locations
what is primary TB?
(1st exposure and up to 5 years afterwards)
- inhaled organism phagocytosed and carried to hilar lymph nodes, immune activated leads to granulomatous response in nodes usually with killing of organism.
- in a few cases infection is overwhelming and spreads.
- tissue changes; small focus (ghon focus) in periphery of mid zone of lung) and large hilar nodes.
what is secondary TB?
- reinfection or reactivation of disease in a person with some immunity
- disease tends initially to remain localised, often in apices of the lung
- can progress to spread by airways or bloodstream.
- tissue changes; fibrosing and cavitating apical lesion.
