S9.1 Tuberculosis Flashcards
Describe the microbiology of Mycobacterium tuberculosis
Non-motile rod shaped bacteria, obligate aerobe. Stains with acid fast stain; gram stain cannot pass through the wall so we do a Ziehl-Nielson stain.
How is TB transmitted?
Respiratory droplets through coughing or sneezing which reach lower airway.
Outline the initial pathogenesis of TB
Inhaled aerosols get engulfed by alveolar macrophages, enter local lymph nodes and form primary complex (Gohn’s focus)
Outline the later pathogenesis of the primary complex in TB
Shall either progress to primary active disease (5%), or initially be contained then go on to latent infection, of which;
95% heals/self-cure
5% reactivates into post-primary TB (pulmonary or extra-pulmonary)
Outline the main difference of latent vs pulmonary TB
With latent: CXR normal, no symptoms, sputum -ve for bacilli
Describe the histology of TB
A caseating granuloma in the lung parenchyma or mediastinal lymph nodes, with Langhan’s giant cells
What are the risk factors for developing post-primary TB?
Caused by reactivation or exogenous re-infection.
HIV, substance abuse, prolonged corticosteroid use, low weight, DM.
What are the risk factors for TB?
Non-UK born, HIV, young and elderly, close contacts of TB, drug users.
What are the symptoms of TB (pulmonary)?
Cough, fever, weight loss, night sweats
What investigations are done in TB?
CXR: ill-defined patchy consolidation in apex
Sputum: smears (Ziehl-Nielson [acid fast] stain)
Histology: granuloma
Tuberculin skin tests
Interferon gamma-releasing assays: cannot distinguish between latent and active
What are the different types of TB?
Pulmonary: found in lungs
Extrapulmonary: places other than the lungs such as brain or kidneys
Miliary: bacilli are carried in the blood to other body parts affecting multiple organs
What are some effects of extrapulmonary TB?
Lymphadenitis
Ascites
Renal disease
Meningitis
How can TB be prevented?
Notification - report all cases to public health
Control - use PPE
BCG vaccine
What is the management for TB?
RIPE for 6 months Rifampicin Isoniazid Pyrazinamide Ethambutol
