Tuberculosis Flashcards
What micro-organism causes TB?
Bacteria called Mycobacterium tuberculosis
TB infections are sometimes called latent.
What does this mean?
When the person is infected with M. tuberculosis but does not have active disease
What proportion of latent TB infections go on to become active?
About 10%
Are people with latent tuberculosis infectious?
No, only people with active disease can infect other people
Why do you have to monitor people with latent TB?
Because their infection could become active at any time, particularly as they age, or if they become immunocompromised
Who gets TB?
1/3rd of the world’s population is infected with TB
Mostly in developing countries nowadays
Immunocompromised people are susceptible, especially HIV patients
How is M. tuberculosis spread?
Droplet spread
Sustained close contact with infected person
Risk factors for getting TB?
HIV Overcrowded living conditions Ethnic minority groups Malnutrition IV drug use Chronic lung disease Immunosuppression
Pathogenesis of TB in a non-immunocompromised person?
Bacteria get to the alveoli
They are engulfed by alveolar macrophages which try to kill the bacteria but are unable
Bacteria replicate in the macrophages
Lymphocytes surround the infected macrophages
Creating a granuloma
The infected macrophages die as well as the bacteria, this creates granulomatous caseous necrosis
The infection goes no further, leaves calcified granulomatous lesions
What is the Ghon focus?
The primary site of TB infection in the lungs
Where is the Ghon focus usually?
Upper lobe of the lungs
Pathogenesis of TB in an immunocompromised person?
Bacteria are ingested by macrophages as they are in a normal person, macrophages are unable to kill the bacteria
The lymphocytes do not surround the infected macrophages sufficiently enough to prevent spread of the infection
Bacteria escape from macrophages and enters blood stream: extra-pulmonary TB
Also, the necrotic material from the granuloma drains into bronchi where it is coughed up as sputum and can infect others
What is miliary TB?
When a TB infection is able to get into the blood stream and spread through the body setting up many foci of infection
Difference between pulmonary TB and extra-pulmonary TB?
Pulmonary: infection contained within the lungs
Extra-pulmonary: infection entered the blood stream and spread around the body
What is a granuloma in TB?
The dead or dying infected macrophages and cell debris from them
Surrounded by epithelioid cells
Surrounded by T and B lymphocytes
How do the macrophages try to destroy the bacteria and why do they fail?
They use reactive oxygen species
They fail because the bacteria has a thick, waxy mycolic acid capsule to protect them from damage
Clinical features of TB?
Most people only exhibit pulmonary features:
- cough
- haemoptysis
- SOB
- constitutional symptoms
Others get extra-pulmonary features:
- other organs affected
What are constitutional symptoms?
Pyrexia Night sweats Fatigue Weight loss Anorexia Lymphadenopathy
Which organs can TB affect? Except the lungs.
CNS Eyes CVS Renal GI Skeletal Skin
Effect of TB in the CNS system?
Meningitis
Effect of TB in the eyes?
Choroiditis, causing blurred vision and red eyes
Effect of TB in the CVS system?
Constrictive pericarditis
Effect of TB in the renal system?
Dysuria
Haematuria
Effect of TB in the GI system?
Ileocaecal, abdominal pain
Ascites
