tuberculosis Flashcards
what is tuberculosis?
it’s an infectious disease caused by Mycobacterium tuberculosis, a small rod-shaped bacteria (a bacillus).
describe 3 characteristics of the M. tuberculosis bacteria
- slow dividing
- high oxygen requirements
- difficult to culture in the lab
how is TB spread?
inhaling saliva from infected people
what are some risk factors?
- Age: Elderly, Neonates
- Male
- Co-Morbidity: Diabetes, HIV, Malnutrition
- Immunosuppression
- Social: homeless, alcohol dependency, drug use, mental health problems
describe 4 outcomes of TB:
Immediate clearance of the bacteria
Primary active tuberculosis (active infection after exposure)
Latent tuberculosis (presence of the bacteria with no symptoms and not contagious)
Secondary tuberculosis (reactivation of latent tuberculosis to active infection)
what is the disadvantage of m. tuberculosis waxy coat?
makes gram staining ineffective
acid-fast bacilli meaning
resistant to acids used in staining procedure
what special stain is used and what does it do?
Zeihl-Neelsen stain
turns bright red against a blue background
what is Multidrug-resistant TB (MDR-TB)?
strains resistant to more than one TB drug e.g., isoniazid and rifampicin
difficult to treat.
When does disseminated/ severe miliary TB develop?
when the immune system can’t control the infection
describe latent TB
Latent tuberculosis is present when the immune system encapsulates the bacteria and stops the progression of the disease.
when does secondary TB happen?
When latent tuberculosis reactivates
what’s a cold abscess?
a firm, painless abscess caused by tuberculosis, usually in the neck.
They don’t have the inflammation, redness and pain you expect from an acutely infected abscess.
describe the BCG vaccination:
Bacillus Calmette–Guérin (BCG) vaccine involves an intradermal injection of live attenuated (weakened) Mycobacterium bovis bacteria (a close relative of M. tuberculosis that does not cause disease in humans).
This creates an immune response, providing lasting immunity against M. tuberculosis without causing infection.
The vaccine protects against severe and complicated TB but less against pulmonary TB.
Before vaccination, patients need to have a negative Mantoux test.
They are also assessed for the possibility of immunosuppression and HIV due to the risks related to a live vaccine.
It is offered to patients at increased risk of TB
what are the 7 typical symptoms of TB?
Cough
Haemoptysis (coughing up blood)
Lethargy (lack of energy and enthusiasm)
Fever or night sweats
Weight loss
Lymphadenopathy (lymph nodes swelling)
Erythema nodosum (tender, red nodules on the shins caused by inflammation of the subcutaneous fat)
what are the 5 extrapulmonary presentations of TB?
B+J, M, L SL, ST
- Bones and Joints (insidious onset, pain especially at night, swelling, pyrexia, decreased range of motion)
- Lymphadenopathy (painless and rubbery)
- Meningism (if spread to CNS)
- Spinal tuberculosis (Pott’s disease: with kyphosis and cold abscesses which are firm and painless lump on the neck)
- Skin lesions (e.g. erythema nodosum, scrofuloderma/ulcerated skin abscess)
what investigations are used for latent TB?
Interferon-Gamma Release Assays
Mantoux test
describe the Interferon-Gamma Release Assays
- This involves mixing a blood sample of the patient with mycobacteria tuberculosis bacteria
- the test is positive if there is release of interferon-gamma by white blood cells.
describe the Mantoux test
- less reliable than IGRA
- an induration of ≥5 mm is a positive result
- involves an intradermal injection of tuberculin (collection of tuberculosis proteins) which then forms a bleb, this is then measured after 3 days.
What investigations are used for active TB?
chest x-rays and cultures samples
What will primary, reactivated and disseminated miliary TB show on a chest x-ray?
Primary tuberculosis
- patchy consolidation, pleural effusions, hilar lymphadenopathy, small lesion (ghon focus)
Reactivated tuberculosis
- patchy or nodular consolidation with cavitation (gas-filled spaces), typically in the upper zones (high O2 presence)
Disseminated miliary tuberculosis
- multiple bilateral small opacities that resemble millet seeds
Describe different ways you can collect a sputum sample:
Sputum cultures
3 separate sputum samples are collected, 8-24 hours gap, at least 1 early morning sample to culture for sensitivity
Mycobacterium blood cultures (require special blood culture bottle)
Lymph node aspiration or biopsy
How do you treat latent TB?
Isoniazid and rifampicin for 3 months
Isoniazid for 6 months or
Rifampicin for 6 months
How would you treat active TB?
R – Rifampicin for 6 months
I – Isoniazid for 6 months
P – Pyrazinamide for 2 months
E – Ethambutol for 2 months
What are the side effects of these medications?
Rifampicin
- red/orange discolouration of secretions, such as urine and tears.
- It is a potent inducer of the cytochrome P450 enzymes and reduces the effects of drugs metabolised by this system, such as the combined contraceptive pill.
Isoniazid
- peripheral neuropathy.
- Pyridoxine (vitamin B6) is co-prescribed to reduce the risk.
Pyrazinamide
- hyperuricaemia (high uric acid levels), resulting in gout and kidney stones.
Ethambutol
- colour blindness and reduced visual acuity.
Rifampicin, isoniazid and pyrazinamide are all associated with hepatotoxicity and hepatitis
name 3 strains of mycobacteria that cause tuberculosis:
M. tuberculosis
M.africanum
M. bovis (spread by unpasteurised infected cow milk)
