What happens in tuberculosis, exactly?

What is it?

Tuberculosis is an infectious disease caused by a bacteria. It mainly, though not exclusively, affects the lungs. In most infections there are no symptoms, but 10% of these infections develop into active tuberculosis which, if left untreated, kills about half of it’s victims.

The symptoms of tuberculosis include a chronic, bloody cough, fever, sweating at night, and losing weight.

About one third of the world’s population have been infected with tuberculosis at some point. It is much more common in developing countries, with 80% of the population of many Asian and African countries testing positive. Although most cases don’t lead to symptoms, tuberculosis still remains the second deadliest infectious disease after HIV/AIDS. In 2014, there were 9.6 million cases of active tuberculosis, which resulted in 1.5 million deaths.

What causes it?

A person becomes infected with tuberculosis when a bacteria called mycobacterium tuberculosis invades their lungs. People with active tuberculosis spread the bacteria into their environment every time they cough, sneeze, or even speak. A very small amount of bacteria can be sufficient to become infected – one sneeze, for example, releases around 40 000 small droplets, and inhaling just one of these droplets can be enough.

What happens during it?

The bacteria first travel into the small units of the lungs called alveoli, where the transmission of oxygen and carbon dioxide between blood and air takes place. The body soon realizes that there’s something off. It sends to the site big white cells called macrophages, who work by engulfing bacteria and then destroying them inside them. They take the bacteria inside them in a membranous vesicle and then combine that vesicle with another one containing toxic substances – but the tuberculosis bacteria are one step ahead. They are surrounded by a capsule that protects them from the host cell’s attack. After successfully hijacking a macrophage, the bacteria start to multiply while taking the required energy from their host cell, eventually killing it.

The body sends more and more white cells to the area of infection in order to kill the bacteria. They form a kind of lump, with the infected cells in the middle, and white cells eager to kill on the outside. When macrophages normally encounter a microbe, after killing it with toxins they present one of its surface proteins to other white cells so they know what to look for. Now they are not able to do that, so the other white cells are practically blindfolded. The centers of these lumps eventually become completely dead. The lumps can lead to the rupture of vessels in the lungs and cause bleeding. The body realizes that there’s some extra material in the lungs which shouldn’t be there, and coughs the mixture of blood and mucus up. Parts of these bacteria-containing lumps can also break free and travel to other parts of the body with blood. Other complications caused by the lumps are the formation of holes in the lungs, and difficulty breathing as they block airways.

How can it be treated?

Antibiotics are used to kill the bacteria. In people with no symptoms only one type of antibiotics is often used, but in those who suffer from active tuberculosis, several different types are used to produce the most effective outcome. Since tuberculosis is highly infectious, it is very important to stay far from people when the disease is in an active form.



Sources: https://en.wikipedia.org/wiki/Tuberculosis, http://www.intellectualventureslab.com/invent/overview-of-tuberculosis-pathogenesis, http://bestpractice.bmj.com/best-practice/monograph/1039/overview/aetiology.html, http://www.webmd.com/lung/tc/tuberculosis-tb-what-happens, http://www.nhs.uk/Conditions/Tuberculosis/Pages/Treatment.aspx




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