An overview of tuberculosis: infection, immune response and preventive strategies Flashcards
Other names for tuberculosis
TB Consumption Wasting disease Koch’s disease White plague Phthisis Scrofula
how many ppl have been infected with TB? 2006 report
2 billion infected, i.e. 1 in 3 of global population
how many people die from TB annually? 2006 report
1.8 million deaths annually, 98% in low-income countries
how many people are exposed to TB? 2006 report
2 billion is exposed to TB (doesn’t mean ill, but exposed and carry pathogen)
endemic area of TB? (2006 WHO report)
Subsaharan africa = endemic area. South america some parts, former soviet union also.
what pathogen causes TB?
Mycobacterium tuberculosis
describe Mycobacterium tuberculosis
- rod-like
- slow growing
- gram positive
- can be stained by acid fast stain test
how is TB transmitted?
aerosol (coughing, sneezing), typically with few bacilli (don’t need large infectious dose)
enters cell body through resp route, either nose or mouth. Goes to lung.
typically, infects and survives in lung macrophages
what does TB start as?
lung disease
TB risk factors?
household sharing and crowded public areas
in most people what happens?
In most people, bacteria are eliminated by phagocytic cells in the lungs. However, in some individuals (5-10 %), not all bacteria are eliminated and some survive and begin to divide.
what % of infections result in TB?
only 10%, hence why 2 billion exposed, but not ill.
What is ‘normal’ outcome of interaction?
Host: 90% of infections do not result in disease - therefore, disease is anomaly
Bacteria: infection without disease is dead end - therefore, disease is a necessity to get to next host.
Best case scenario, infect many but have disease in minority. Only small proportion will transmit.
when happens once TB is in the body?
Granulomas are formed from infiltrating cells surrounding the infected cells and serve the purpose of containing the spread of infection.
They also provide a milieu for cell-cell interactions that may facilitate bacterial removal.
Inhale droplets from cough / sneeze from infected person.
Cough will create visible droplets as well as fine aerosol which you can’t see.
Remain in air for prolonged period of time, several hours. Likely source of new infection. (The visible droplets unlikely source of new infection)
TB initially forms granuloma in lungs which can be seen in a chest X-ray.
Host cells grouping around to isolate bacteria, limit spread. And possible eradicate it.
Sometimes the immune response works. If it fails, lesions breaks and liquefies spreads to other part of lung.
Course of M. tuberculosis infection
- primary
- latent
- reactivated
Latent TB
1/3 world’s population infected
BCG largely ineffective
Preventive drug treatment possible but not practical
Reactivation many years later
Risk factors for reactivation
Malnutrition Immunodeficiencies - HIV IS A BIG FACTOR Immunosuppression Old age Poor health HIV
can latent TB and active TB be treated in the same way?
can treat latent TB like active. However, it’s not practical / economical bc don’t always know who has latent TB and not all latent TB progresses to active TB.
