Revision Flashcards
What bacteria causes TB?
Mycobacterium Tuberculosis
What are the properties of mycobacterium tuberculosis?
- thick cell wall
- slow growing (hence TB progresses slowly and treatment is long)
- aerobic
- very tough
- found in the soil
- non motile
- stained by ZN stain
30% of TB is due to different types of bacteria. What are their names? 5
M. auium-intracellulare M. kansasii M. malmoense M. xenopii M. leprae
How is TB infection transmitted between people?
A TB patient coughs/sneezes and brings up bacteria from the infected lobe (apical cavity)
The droplets of bacteria evaporate.
The bacteria remain airborne for long periods of time.
The mycobacterium is inhaled.
Not many bacterium are required to infect someone.
Describes what happens when mycobacterium reach the alveoli.
The mycobacterium grow slowly but are not destroyed as the body doesn’t have any immunity to the bacteria and the mycobacterium is very tough so macrophages find it hard to digest the bacterium.
T helper cells recognise the mycobacterium.
T helper cells activate the immune system (antigen presenting cells and macrophages)
Macrophages produce toxins to enable them to destroy the bacterium but the mycobacterium is protected by their thick cell walls. However, during this process, the toxins damage the local tissue and can cause necrosis.
Epitheloid cells (activated macrophages) -> Langhans giant cells -> accumulation -> granuloma -> central caseating necrosis (may calcify later)
What are the two factors that affect the tissue damage?
Infection
Susceptibility (age, genetics, race, nutrition) - fluctuant
Describe the two natural histories of TB?
Primary
- usually no symptoms
- Ghon focus + primary complex (forms a cavity)
- Primary can progress to progressive primary in about 1% of people. Usually occurs about 6-12 months after infection as the immune system has given up after being infected and bacterium take over the body. Usually has a poor prognosis
Post primary
-Reactivation of latent primary infection
OR
-new reactivation from outside source (susceptible previously infected host)
- sometimes no symptoms
-can occur at any ages after being infected with TB
State some consequences of TB.
Primary focus can enlarge and form a cavity.
Enlarged hillier lymph can compress the bronchi and can cause a lobar collapse.
Enlarged lymph gland can discharge into the bronchi.
Tuberculous bronchopneumonia
Describe the symptoms of TB
Disease progression is slow Usually the infection starts asymptomatic After several months: -cough -sputum -haemoptysis -SOB -pleurtic pain -malaise -fever -night sweats
state some investigations for TB
Sputum culture (ZN stain) CXR - patchy shadowing (often in apex) -cavitation (if advanced) -multifocal consolidation -may calcify if chronic or healed CT trans thoracic biopsy Bronchoscopy Pleural aspiration (if there is pleural effusion) Mantoux test
Describe the treatment for TB
Fresh air, nutrition, bed rest, vitamin D and cathelecidin (LL-37)
Multi drug therapy: Rifampicin Isoniazid Ethambutol Pyrazinamide
Surgery:
less commonly done
but sometimes done to try to collapse the cavity the bacterium are in to create anaerobic conditions so the bacterium would die.
State the side effects for Rifampicin Isoniazid Ethambutol Pyrazinamide
Rifampicin:
- orange “irn bru” urine and tears
- hepatitis
- induces liver enzymes, anticonvulsants, prednisolone
Isoniazid:
- hepatitis
- peripheral neuropathy
Ethambutol:
-optic neuropathy
Pyrazinamide:
-gout
State one way the TB can be prevented
BCG vaccination
Describe some facts about TB such as where it is most likely to occur and the death rate world wide
Disease of poverty and overcrowding. Migration is a may cause for the infection to be spread around the world. 2 billion infected 8.6 million new cases annually 1.3 million deaths annually
can mycobacterium tuberculosis remain airborne for long periods of time?
yes
