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Tuberculosis is caused by Mycobacterium tuberculosis and symptoms include chronic cough, chest pain, weight loss, and fever. Diagnosis is confirmed through chest X-rays, skin tests, and sputum tests. The infection begins in the lungs and progresses to form granulomas, causing tissue destruction and scarring.
Tuberculosis, or TB, is a common disease; about a third of the world’s population has been exposed, but most people remain asymptomatic. People who have an active TB infection tend to experience a classic pattern of symptoms and signs. Symptoms of tuberculosis typically include a chronic cough that can produce bloody sputum, chest pain, weight loss, and fever.
In humans, tuberculosis is caused by Mycobacterium tuberculosis, a bacterium that infects the lungs. The diagnosis of tuberculosis is confirmed based on chest X-rays, skin tests, and sputum tests, as a person with tuberculosis will have the bacteria in their sputum. Sputum is matter that has been expelled from the lower respiratory tract and airways and contains mucus, saliva, and any bacteria that infect the lower airways and lungs.
Preliminary diagnosis is typically made on the basis of any tuberculosis symptoms that may be present. The most common signs and symptoms of TB include a chronic cough, bloody sputum, night sweats and fever, aching chest pain, and unexplained weight loss. A person with these symptoms will usually be referred for chest x-rays, sputum tests, and other tests to confirm a diagnosis of tuberculosis.
Symptoms of tuberculosis are the result of infection by the bacterium M. tuberculosis. The infection begins when the bacteria begin to colonize the air sacs of the lungs. Once colonization begins, the bacteria are ingested by immune cells called macrophages, a type of cell responsible for ingesting and decomposing bacterial cells and cellular debris. Macrophages typically have no problem digesting bacteria; however, they are unable to kill the M. tuberculosis bacteria they have ingested.
As the infection progresses, other immune cells, including T and B cells, begin to gather around the infected macrophages. The immune cells form lumps called granulomas, which are small regions of infected macrophages surrounded by T and B lymphocytes. The immune system forms granulomas in cases where the immune cells cannot clear the infection; instead of killing the pathogen, the immune system isolates the infected area by surrounding it with a barrier of cells. Inside granulomas, lymphocytes secrete cytokines to help kill invading bacteria.
The classic symptoms of tuberculosis, including bloody sputum, the characteristic cough and fever, are all caused by this chronic infection. The pattern of infection can include multiple cycles of granuloma formation, tissue destruction, and healing, and can last for years and even decades if the disease is left untreated. As the infection progresses, the lung tissue progressively scars, reducing lung function for affected individuals. Infected people also become more contagious as the disease progresses, because as their lung tissue becomes more necrotic they are more likely to cough up infected material.
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