Lecture objectives
- Recognise mycobacterium tuberculosis, the causative organism of tuberculosis, and describe its mode of transmission
- Outline the immune response to mycobacterium tuberculosis organisms, an example of type IV hypersensitivity and recognise the granuloma as the hallmark of TB infection
- Describe the pathological features of primary pulmonary TB, namely, the Ghon complex and list the possible outcomes following primary infection, including miliary TB
- Describe the pathogenesis and pathological features of secondary, reactivation, reinfection pulmonary TB
- Describe the pathogenetic and morphology of extra pulmonary ot isolated organ TUberculosis
- Describe the principles of diagnosis and treatment of tuberculosis
Context
TB is a worldwide, historical disease
Tuberculosis: causative organism
Mycobacterium Tuberculosis
Transmittion is through aerosolised particlues prolonged contact is needed for transmittion miliary TB alone is not transmitable directly latent infection is not infectious
upon exposure only 30% are nfected and only 5-10% develop active disease
BCG vaccine uses attenuated bovis strain
Pathogenesis
M. Tuberculosis travels deep into lung and get phagcytosed by alveolar macrophages. they reproduce intracellularly bacterial proliferation within lung leads to bacteraemia and seeding of organs. most people within this are asymptomatic
about 3 weeks after infection T cell mediated response begins
mycobacterial antigens in the hilar lymph nodes lead the T-cells to differentiate into Th1 cells which make IFN-y this makes macrophages fight better and longer
granulomas
Activated macrophages called epithelioid cells form TB granulomas to contain TB (contain langhans giant cells)
Granulomas develop central caseous necrosis as a result of immune response
granulomatous infection is a type os chronic inflammation they can be present in deveral diseases and can even be formed as a reaction to a foreign body example of type 4 hypersensetivity
Primary infection - Ghon complex
area of primary infection in the lung that develops granulomsas and caseous infeciton is called the ghon focus. hilar lymph nodes also develop granulomas and along with the ghon focus form the ghon complex
possible outcomes after primary infeciton
you can either get better or get latent disease. Primary complex can lead to progressive primary tb which can lead to miliary TB Miliary TB is seeding of tb and granulomas all over the body
secondary TB is reactivation and following immune response this can also be called chronic fibrocaseuas TB
Sometimes miliary tb can become secondary tb without pulmonary symptoms
isolated organ TB can be seen in any tissue or gan
lymph nodes are the most likely location for ExPul tb (historically known as scrofula)
potts disease si tuberculous osteomyelitis
you can also get tuberculous meningitits (look for granulomas)
diagnosis of TB
definite diagnosis is isolationof organisms from sputum sample or a tissue sample from infected extrapulmonary site
clinical findingd consisten with active pulmonary diease ( night sweats with fever) chest x ray mantoux test (tuberculin skin test) or interferon gamma release assay