The above image shows a coloured X-ray of pulmonary tuberculosis, caused specifically by the bacterium Mycobacterium tuberculosis.
TB is most commonly caused by the bacterium Mycobacterium tuberculosis (MTB), which is spread by droplet infection (transmitted in saliva, usually by coughing or sneezing). MTB is highly aerobic, requiring high levels of oxygen. It affects the respiratory system, particularly damaging and destroying lung tissue.
Only about 30% of people exposed to TB will become infected. This is much more likely to occur in individuals who are immunocompromised (hence TB often presenting itself in those whom are HIV positive).
The primary infection of TB is often asymptomatic, although occasionally it may cause fever and/or a dry cough. In an individual with a healthy immune system, a localised inflammatory response will occur, forming a nodule of tissue called a tubercule (containing dead bacteria and macrophages). Typically (in about 90% of cases) the condition will resolve itself without the individual ever having known they were infected.
However MTB may survive, as alveolar macrophages are unable to digest the bacteria, allowing it to remain in a state of dormant latency and multiply silently. After a period of time, when the host’s immunity is compromised (for example, due to infection or malnourishment) the bacteria will produce active tuberculosis.
When the infection presents itself in this way (referred to as miliary tuberculosis), symptoms may initially include loss of appetite, fever, productive cough and loss of energy, loss of weight/anorexia or night sweats however these are very non-specific. As the infection progresses, one may develop tuberculous pleuritis (causing chest pain, nonproductive cough and fever), increase in production of mucous and haemoptysis (coughing up blood).
As the infection spreads it may lead to symptoms such as abdominal pain, painful urination, sterility and brain damage (depending on which areas are affected and to what extent).
Treatment and prevention:
If left untreated, TB will eventually cause death. This may be because of hypoxia (due to severe lung damage) or organ failure (due to malnutrition). Also, as TB disarms a critical part of the immune system, it makes patients much more susceptible to opportunistic infections (such as pneumonia) therefore patients are often treated with antibiotic medication outside of a hospital environment. Vaccines are commonly administered as a form of prevention and are effective against severe forms of paediatric TB however adult pulmonary TB is still prevalent (there are currently more TB cases worldwide than ever before).
An X-ray may indicate the presence of TB however other infections appear similar so cultures must be taken to confirm the diagnosis.