Summary
Summary Medical Microbiology - Tuberculosis notes
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Introduction, Transmission, Exposure Consequences, Disease Progression, Diagnosis, Control Methods, Example Case Study Questions, Case Study Notes
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TuberculosisIntroduction
● Incidence increasing (esp in developed countries) but death rates declining
● Many factors contribute to infection but it is non-discriminatory to people from all ages, background, race
etc.
● Multi-drug resistant TB (MDR TB) becoming a problem
● Co-infection with HIV is most common cause of death for those who are HIV+. Appear to speed up progress
of on another. TB often harder to diagnose as lower particles in sputum samples compared to pleural fluid. If
treated for, medication of the two should be checked to not cause adverse effects
Transmission
● Airborne disease. Droplet nuclei can contain 1000s of the bacteria bacilli. Cough/sneeze/breathing can cause
infection
● Can be zoonotic from unpasteurised cow's milk, M. bovis
● Transmission affected by: proximity, length, frequency and level of physicality of exposure, ventilation, air
circulation, enclosed spaces
● Risk of disease affected by: level of immunity/immunosuppression, infecting dose (10 bacilli needed only),
virulence, vaccination
Exposure Consequences
● Healthy individual can clear mycobacteria bacilli easily if they are few in number. Macrophages engulf and kill
● Latent TB appears asymptomatic at first but can be reactivated to cause secondary infection. TB is contained
within macrophages upon initial infection and not able to replicate; non infectious
● If macrophages unable to take up bacilli, bacilli burst out, multiply and cause local tissue damage and even
dissemination. This is called active/progressive TB; very infectious
Disease Progression
● Stages: onset (1-7 days) is inhalation from air and engulfing by alveolar macrophages →
symbiosis (7-21 days) is replication from within macrophages → initial caseous/cheesy
necrosis (14-21 days) is tubercle formation and granuloma maturation which can begin to
necrotise and show up in sputum/around the body
● Immune response if TB spreads to lymph nodes are nonspecific and are general so diagnosis is difficult
● X rays show opaque areas in upper lungs (shows transparent) which are caseous cavities and local tissue
destruction around tubercles
● Gross pathology shows ‘cheesy’ deposits ie necrosis
● Cough of patients is prolonged and deep + green/yellow/bloody sputum
● Stethoscope reveals bronchial distress
● Other symptoms can be weight loss, chest pain, general malaise
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