Tuberculosis Flashcards
What is the prevalence of TB?
2 billion people infected worldwide. 8.6 million new cases each year, 1.1 million HIV positive and 75% are in Africa. 2nd leading cause of death from infectious disease worldwide. 1.3 million deaths annually.
Why is TB re-emerging in London?
Immigration from high incidence areas.
Which 2 species of Mycobacterium cause TB?
Mycobacterium TB and Mycobactrerium bovis (bovine TB). Mycobacterium are ubiquitous is soil and water.
Name some features of Mycobacterium.
Non-motile; very slow growing; aerobic so prefers apices of lungs; thick cell wall (peptidoglycan, lipids and arabinomannans); resistant to acids/alkalis/detergents; resistant to macrophage/neutrophil destruction; AAFB.
How is M.TB transmitted?
From a case of open pulmonary TB (coughing and sneezing); respiratory droplet transmission, M.TB can remain airborne for long periods. Outdoors, M.TB eliminated by UV radiation. It is smaller droplet nuclei that are a problem as they can reach the alveoli.
How is M.bovis transmitted?
Consumption of infected cows milk. Organisms deposited in cervical and intestinal lymph nodes.
Describe the immunopathology.
Th1 response: activated macrophages –> epithelial cells –> Langerhans giant cells. These accumulate and form a granuloma. Central caseating necrosis which may later calcify. Macrophages reduce bacteria but also cause tissue destruction.
Which factors determine susceptibility of a host?
Age (elderly), nutrition status (malnourished) and immunosuppression status.
Describe a natural primary infection.
No immunity, usually children. M.TB spreads via lymphatics to all areas of body. Usually asymptomatic, can be malaise. In 85% initial lesion in local lymph node heals without scar. Immune to tuberculoprotein.
In 1%: primary focus enlarges, > hilar lymph nodes compress bronchi & discharges into bronchus –> tuberculous bronchopneumonia (poor prognosis).
In 1%: 6-12 months after infection - miliary TB (widespread, small granulomas), meningeal TB or tuberculous pleural effusion.
What can happen post-primary disease?
Reactivation of M.TB from dissemination (usually) or new re-infection from outside source - can lead to progressive disease. Eg. pulmonary disease, male/female infertility, spine, hip etc. This typically occurs 1-5 years after primary.
Describe the history of someone with post-primary TB.
PC/HPC: cough, sputum, haemoptysis, pleuritic pain, SOB, night sweats, malaise, fever. PMH: diabetes, some sore of immunosuppression, previous TB. Drugs: immunosuppressive. PSH: alcohol, IVDA, immigration.
What are the clinical signs of post-primary TB?
Mostly none. Advanced: crackles/bronchial breathing.
How is TB diagnosed?
Suspect: immunosuppressed, malnourished, diabetic, elderly, immigration.
Essential investigations: 3 sputum specimens on 3 successive days (sputum smear, culture or PCR). CXR - bilateral, patchy shadowing, calcification from previous TB, cavitation.
Further investigations: bronchoscopy with bronchoalveolar lavage; pleural aspiration and biopsy if effusion.
What was the old treatment of TB?
Sanatorium regime - fresh air, sunshine, bed rest, good food etc. Sometimes surgery, 5YS cavitating disease: 25%.
What is modern TB treatment?
MD therapy - treatment with a single agent leads to drug resistant organisms within 14 days. Therapy for 6 months. Must notify all cases.
