Tuberculosis Flashcards
Why was there a decline in TB incidence pre 1980s?
There was advancements in housing, better diets and hygiene.
Where in the UK is TB a major problem?
- West Midlands
- London
What bacteria is responsible for TB?
Mycobacteria
Where do mycobacterium live?
In soil and water
What species of mycobacterium are responsible for TB?
- Mycobacterium tuberculosis
- Mycobacterium bovis
What species of mycobacterium is responsible for leprosy?
Mycobacterium leprae
What other species of mycobacterium are there?
- M. avium-intracellulare
- M. kansasii
- M. maimonese
- M. xenopii
What kind of disease is TB?
Very slow grow growing, progressive disease that requires long treatment
What kind of bacteria is mycobacterium?
- Non-motile bacillus
- Aerobic
Where does mycobacterium have a predilection for?
Apices of the lungs
Describe the structure of mycobacteria.
- Very thick cell wall
- Contains lipids, peptidoglycans and arabinomannans
What is mycobacteria resistant to?
- Acids, alkalis and detergents
- Neutrophil and macrophage destruction
What test is used to identify mycobacteria?
Acid and alcohol fast bacilli using a ZN stain
What is the source of transmission of mycobacteria?
- Respiratory droplets evaporate
- Droplet nuclei contain mycobacteria
- Droplets remain airborne for very long periods
How are outdoor mycobacteria eliminated?
By UV radiation and infinite dilution
What happens when mycobacteria droplets are inhaled?
- Larger droplet nuclei impact on large airways and are cleared
- Small droplet nuclei organisms impact in alveoli and slowly proliferate.
How is TB contracted through mycobacterium bovis?
- Consumption of infected cows milk
- Deposited in cervical and intestinal lymph nodes
How do activated macrophages cause necrosis?
- Activated macrophages can kill off TB organisms but at the same time they release enzymes and free radicals which cause tissue damage
- Acculmulation of macrophages, epithelioid and Langhan’s cells cause granulomas
- Central caseating necrosis which may later calcify
What mediates the immunological response?
Th1 cells
What does the Th1 mediated immunological response lead to?
- Elimination/ reduction in number of invading mycobacteria
- Tissue destruction as a consequence of activation of macrophages
What factors affect susceptibility?
- Genetics
- Race
- Nutrition
- Age
- Immunosuppression
What affects outcome of infection?
- Virulence
- Number of organisms
How might a resistant host become a susceptible host?
With age
How might a susceptible host become a resistant host?
With a better diet
Who is usually affected by primary infection?
Usually children with infected focus in alveolus
How is mycobacteria spread in the body?
- Spread via the lymphatics to draining hilar lymph nodes.
- Haematogenous seeding of mycobacter to all organs of the body
What are the symptoms of primary infection TB?
- Usually no symptoms
- Can be fever
- Malaise
- Erythema nodosum
- Rarely chest signs
What occurs in most people with primary infection?
- Initial lesion and local lymph node creating primary comlex
- Heals with or without scar which may calcify creating Ghon focus
What is primary infection associated with?
Development of immunity to tuberculoprotein
What does intra-dermal administration of tuberculoprotein result in?
Lymphocytic and macrophage based area of inflammation after 48 hrs
What are the 3 outcomes of primary infection?
- Progressive disease
- Contained latent
- Cleared and cures
How can a primary infection progress?
- Primary focus continues to enlarge and forms a cavity
- Enlarged hilar lymph compress bronchi causing lobar collapse
- Enlarged lymph node discharges into the bronchus causing tuberculous pneumonia
What occurs in some individuals 6-12 months after infection?
- Miliary TB fine mottling on X-ray, wide-spread granuloma
- Meningeal TB, severe, CSF high protein, lymphocytes
- tuberculosis pleural effusion
What are 2 mechanisms of post primary disease?
- Reactivation of mycobacterium from latent primary infection disseminated by the blood stream around the body
- New re-infection from outside source, susceptible previously infected host
What tissues can TB affect?
Just about any
When may post primary pulmonary tuberculosis occur?
At any age but there may be no symptoms for many months
What are the respiratory symptoms of post primary pulmonary tuberculosis?
- Cough
- Sputum
- Haemoptysis
- Pleuritic pain
- Breathlessness
What are the systemic symptoms of post primary pulmonary tuberculosis?
- Malaise
- Fever
- Weight loss
- Night sweats
Past medical history of post primary pulmonary TB.
- Diabetes
- Immunosuppressive diseases
- Previous TB
Drug history of post primary pulmonary TB.
Immunosuppressive drugs
Personal/social history of post primary pulmonary TB.
- Alcohol
- IDVA
- Poor social circumstances
- Immigrants from high incidence areas
What are the signs of post primary pulmonary TB?
- May be none
- Advanced: crackles, bronchial breathing
- Finger clubbing very rare unless in chronic infection
Who is included in high index of suspicion?
- Immunosuppressed
- Malnourished
- Alcoholics
- Vagrants
- Previous gastric surgery
- Malignancy
- Diabetes mellitus
- Adolescents, elderly
- Recent migrants from high prevalence countries
What essential investigations are there?
- Sputum sample
- Chest X-ray
How is sputum sampling carried out?
- 3 sputum samples on successive days
- Sputum smear- ZN stain- immediate answer if AAFB
- Sputum culture which can take 8 weeks
What might be observed on a chest x-ray?
- Patchy shadowing, often apices/upper zones or apex of lower lobe
- Cavitation if advanced
- May calcify if chronic or healed TB
What further investigations can be carried out if the sputum samples are negative?
- CT scan of thorax
- Bronchoscopy with bronchoalveolar lavage, transbronchial biopsy
- Pleural aspiration and biopsy if pleural effsuion
What was the treatment of TB up until 1950?
- Fresh air
- Sunshine
- Bed rest
- Good food
- Improving immunity
- Vitamin D and cathelecidin
What surgery was used to treat TB?
- Collapse down the cavity
- Anaerobic conditions- phrenic crush
- Artificial pneumothorax
- Pneumoperitoneum
- Thoracplasty
- Lung resection
What are the rules for modern treatment of TB?
- Multiple drug therapy is essential
- Single agent treatment leads to drug resistance organisms with 14 days
- Therapy must continue for at least 6 months
- TB therapy is a job for committed specialists only
- Legal requirement to notify all cases
- Low threshold for HIV testing, AIDS defining condition
What drugs are patients on for 2 months?
- Rifampicin
- Isoniazid
- Ethambutol
- Pyrazinamide
What drugs are patients on for 4 months?
- Rifampicin
- Isoniazid
When is TB rendered non-infectious?
After 2 weeks
What are the side effects of rifampicin?
- Orange urine
- Tears
- Induces liver enzymes which alter metabolism of prednisolone and anticonvulsants
- OCP ineffective
- Hepatitis
What are the side effects of isoniazid?
- Hepatitis
- Peripheral neuropathy
What are the side effects of ethambutol?
Optic neuropathy
What are the side effects of pyrazinamide?
Gout
What does likelihood of infection with TB depend on?
- Duration of contact
- Intensity of infection
Who should be screened first?
Close household contacts
If the close contacts have been infected who should be screened?
Casual contacts
What are the tuberculin tests?
- Mantoux
- Heaf
Who should have no immunity to tuberculoprotein?
-Younger than 16 with NO BCG
What should be carried out if there is a positive heaf test?
Chest x-ray
If the chest x-ray is normal what should be done?
Chemoprophylaxis to kill mycobacteria
If the chest x-ray is abnormal what be done?
Treat as TB
If the heaf test is negative, what should be done?
- Repeat test after 6 weeks
- If 2nd test negative= BCG
- If 2nd test positive= recent infection
If someone is over 16 and has a BCG then how should they be screened?
- Chest x-ray
- Normal= reassure and discharge
- Abnormal= investigate and treat
