Tuberculosis COPY Flashcards
Describe the global distribution of tuberculosis.
TB is the number 1 killer of communicable diseases. TB kills more than HIV and Malaria together.
2/3 of all TB cases (prevalence) in 8 countries:
India (27%),
China (9%),
Indonesia (8%),
the Philippines (6%),
Pakistan (5%),
Nigeria
These and 22 other countries in WHO’s list of 30 high TB burden countries
accounted for 87% of the world’s cases
An estimated 2 billion people are infected worldwide
Describe the impact of the global distribution of tuberculosis on tuberculosis in the UK.
One of the most vulnerable groups in the UK are those from high prevalence countries.
Describe the epidemiology of tuberculosis in the UK.
Rate of TB increases as deprivation decile increases. 15 every 100 thousand at 1 decile and < 5 every 100 thousand at the 10th decile.
Vulnerable groups in UK -
- those from high prevalence countries,
- 70% are non-UK born most aged between 15 and 44.
- HIV positive immunosuppressed
- Elderly, neonates, diabetics
- Homeless, Alcohol dependency, IVDU’s, those with
mental health problems and those in prisons – approximately 1 in 10 of all cases**
Describe features of Mycobacteria.
Numerous species, ubiquitous in the soil, water
Non-motile bacillus, very slowly growing (disease is slow, treatment is long)
* Aerobic (predilection for apices of lungs)
* Uniquely has a very thick fatty cell wall
* Resistant to acids, alkalis and detergents
* Resistant to neutrophil and macrophage destruction
* Acid - and alcohol - fast bacilli (AAFB) (Ziehl Neilson stain)
* Not all AAFBs are TB
Describe the transmission of tuberculosis.
Airborne (pulmonary & laryngeal TB spreads, the others not so much)
* Someone with TB bacteria in their lungs coughs (sneezes, yells, sings)
* TB bacteria attached to aerosol droplets which can remain suspended in air for many hours, especially if there is poor air circulation
* Someone else breath these bacteria in
* Usually requires prolonged close contact
* Outdoors mycobacteria eliminated by UV radiation and dilution
Exception to rule of how TB is spread is Mycobacterium bovis, which can be spread by consumption of unpasteurized infected cows’ milk (very uncommon in the U.K.)
NOT spread by
- Shaking hands
- Sharing food
- Touching surfaces
- Sharing toothbrushes
- Kissing
Describe species of mycobacteria that cause human disease.
A few species responsible for human disease
* Tuberculosis (M. tuberculosis, M.africanum, M. bovis (“bovine TB”, BCG strain) * Non-tuberculous mycobacteria, NTM-infections / ‘Atypical mycobacteria
* Leprosy (M.leprae)
Describe the host immune response to TB.
TB bacteria enters alveoli -> macrophages ingest bacteria -> helper T cells come from lymph and release chemicals which activate macrophages.
- Activated macrophages -> epithelioid cells -> Langhan’s giant cells
- Accumulation of macrophages, epithelioid & Langhan’s cells
-> GRANULOMA - Central caseating necrosis (may later calcify)
Describe how the majority of individuals are affected by TB.
In the majority (>85%)
Initial lesion + local lymph node (Primary complex)
Heals with or without scar. May calcify (Ghon focus + complex)
Associated with development of immunity to tuberculoprotein
Describe primary infection of TB
Not the most common clinical presentation of TB.
No preceding exposure or immunity
Mycobacteria spread via lymphatics to draining hilar lymph nodes
Usually no symptoms, can be fever, malaise. Erythema nodosum, rarely chest signs
Describe the three pathways of primary infection of tuberculosis.
- Progressive disease
- Contained latent
- Cured
Describe the pathogenicity of TB in it’s progressive primary form.
In a small number (1%)
Primary infection progresses to Tuberculous bronchopneumonia
Primary focus continues to enlarge - cavitation Enlarged hilar lymph compress bronchi, lobar collapse Enlarged lymph node discharges into bronchus
Poor prognosis
In a small number (1-3%)
Miliary TB (looked like millet seeds on autopsy) develops, with hematogenous spread of bacteria to multiple organs
Fine mottling on X-ray, widespread small granulomata CNS TB in 10-30%
Describe how post primary TB arises.
Post-primary (adult type) tuberculosis develops preferentially in people with sufficient immunity to clear and heal caseating granulomas of primary tuberculosis
Describe the hypothesis behind post primary disease.
Two main hypothesis
1. TB bacteria entering a dormant stage with low or no replication over prolonged
periods of time
2. Balanced state of replication and destruction by immune mechanisms
Describe the TB timeline.
Describe clinical presentation of TB.
