(ID)- Tuberculosis Flashcards
What causes TB?
Mycobacterium tuberculosis
What type of bacteria is mycobacterium tuberculosis?
Aerobic acid-fast bacilli
What staining is required for TB and why?
Zeihl-Neelsen stain
Waxy coating
Resistant to acids
What is the disease course of TB?
Immediate clearance
Most cases
Primary active TB
Active infection after exposure
Latent TB
Bacteria are present but not symptomatic or contagious
Secondary TB
Reactivation of latent TB
What is miliary TB?
Immune system unable to control infection
Disseminated and severe disease develops
What are the symptoms of active TB?
Non-resolving cough
Unexplained persistent fever (low or high grade)
Drenching night sweats
Weight loss
What is the histology for TB?
Caseating granulomatous inflammation
When is latent TB present?
Immune system encapsulates bacteria and stops progression of disease
Most patients never develop active infection
What is secondary TB?
When latent TB reactivates and infection develops due to immunosuppression
Where is the most common site for TB infection?
Lung apices to get plenty of oxygen
What is extrapulmonary TB?
TB in other areas e.g.
- Lymph nodes
- Pleura
- CNS
- Pericardium
- GI
- GU
- Bones and joints
- Skin
What is a cold abscess?
Firm, painless abscess caused by TB in the neck
No inflammation, redness or pain
What are the risk factors of TB?
- Close contact with active TB (household member)
- Immigrants from high TB prevalence
- People with relatives or close contacts from countries with a high rate of TB
- Immunocompromised
- Malnutrition, homelessness, drug users, smokers and alcoholics
What is the BCG vaccine?
Bacillus Calmette-Guérin vaccine
Intradermal injection of live attenuated Mycobacterium bovis
Why can Mycobacterium bovis be used for vaccination?
Close relative of Mycobacterium tuberculosis
Does not cause diseases in humans
What does the BCG vaccine protect against?
Severe and complicated TB
Less against pulmonary TB
Before vaccination what test is used on patients?
Mantoux test
Vaccine only given if negative
What are patients assessed for before giving the BCG vaccine?
Immunosuppression
HIV
Due to risk of live vaccine
Who is offered a BCG vaccine?
Healthcare workers
Patients at increased risk of TB
How does TB present?
Chronic, gradually worsening symptoms
Most cases with pulmonary disease with systemic symptoms
- Cough
- Haemoptysis
- Lethargy
- Fever or night sweats
- Weight loss
- Lymphadenopathy
- Erythema nodosum
- Spinal pain in spinal tuberculosis (Pott’s disease of the spine)
What investigations are used for TB?
Ziehl-Neelsen stain
Immune response tests
- Mantoux test
- Interferon-gamma release assay (IGRA)
Suspected disease to support diagnosis
- CXR (mediastinal lymphadenopathy or cavitating pneumonia)
- CT (lymphadenopathy
- MRI (can show leptomeningeal enhancement in TB meningitis)
What is the mantoux test?
Injecting tuberculin into the intradermal space on the forearm
Infection creates a bleb under the skin
After 72 hours skin injection site is looked at, induration of 5mm or more is positive
What is tuberculin?
Collection of tuberculosis proteins isolated from bacteria
What is the interferon-gamma release assay?
Blood sample mixed with antigens from mycobacterium tuberculosis
After previous contact with mycobacterium tuberculosis WBCs become sensitised to bacterial antigens and will release interferon-gamma on contact
Positive result is if interfon-gamma is released
Does not differentiate between active and Latent TB
