TB Flashcards
Factfilr of TB
Aerobic bacilli Non motile Cell envelope which resists gram staining Known as acid fast bacilli Very slow growing
IN which populations have a higher rates of TB
Immigrants from high prevalence countries
HIV positive patients
Homeless, drug users, prisoners
Londoners
How do you catch TB
person with TB coughs and expels infectious droplets and someone else breathes them in
Transmission factors
HIV+ Higher transmission if productive cough Enclosed spaces with poor ventilation TB susceptible to killing by UV Higher exposure= higher risk
Differences between primary disease and latent disease
Inhaled particle and there is an infection straight away
Latent disease- Inhaled particle and can sometimes never reactivate or can reactivate later in life
HOW does a disease progress
TB containing droplets reach the alveoli and are uptake by macrophages
If macrophages fail to kill TB primary infection occurs
- TB in fact then slowly multiplies within macrophages phagosomes - Also means there is the potential for these macrophages to carry TB to local lymph nodes or further around the body.
3) At this point whether active or latent disease occurs depends on a complex interplay between host and bacteria.
- For example: number of TB bacteria inhaled and is the host immunocompetent
What happens in primary disease
Patient fails to clear the bacilli and develop a primary infection of the lungs
TB bacilli proliferate inside alveolar macrophages
This results in a granulomatous lesions beginning to develop in the lungs
This primary lesion may then heal by fibrosis, or the disease may invade locally or disseminate leading to symptomatic primary disease
What happens in latent disease
Over around 2-6 weeks the adaptive immune response kicks in and T cells etc get involved
- This is also useful for some of the tests we can do for TB such as the skin tests
The adaptive and innate immune system interact and a granuloma forms to contain the TB infection
- The TB within the granuloma aren’t dead but dormant – so while they protect the host they also allow the TB to ‘hide’ in the body for many years
Therefore latent TB can always be reactivated depending on what happens to the hosts immune system
Are people with latent TB infectious and have active disease?
What do their CXR look like
No
Normal CXR
WHta is it called when TB reactivates later in life
POst-primary disease
What will post primary TB show on a CXR
show upper lobe pulmonary infiltrates, as well as hilar adenopathy, cavities, effusions and nodules
Who has a higher chance of reactivation
Untreated HIV
Immunosuppressed for other reasons e.g. long term steroids or immunosuppressive drugs such as Anti-tnf following solid organ transplant
Co morbidities such as diabetes and CkD
Aging
Investigating TB
1) Culture -
Pulmonary TB – several early morning sputum samples to look for acid fast bacilli down the microscope and then culture
- Non-Pulmonary TB – a sample from the suspected site to culture
2) Histology – classically will find caseating granuloma
3) Imaging: CXR
In primary TB where will findings be
Anywhere in lung
In primary TB what will findings look like on CXR
Caseating granulomas – if these calcify known as a Ghon focus, and if seen with regional lymphadenopathy a Ghon complex
- These represent healing of a primary TB infection
Lobar or patchy consolidation
Effusions and regional lymphadenopathy
Can also get miliary TB where the TB rapidly spreads throughout the lung fields
- Like ‘Millet seeds’ hence the name
- More common if immunosupressed
