Tuberculosis
What is TB?
TB bacterium under the microscope.
TB bacterium under the microscope.
TB is an infectious disease caused by a bacterium called Mycobacterium tuberculosis. It affects the lungs mostly but can cause symptoms in your skin or other organs. TB is passed on from coughs and sneezes where the bacterium is carried in the air, a third of the population of the world is infected with the tuberculosis bacterium but only one in 10 of these people will go on to develop the disease thanks to your body's immune system, which fights the infection, and usually destroys the germs once it is inhaled. The immune systems that do fight off the bacteria successfully forms a defensive shield around the bacteria and will stay in the body but you won’t suffer from any of the symptoms of tuberculosis this is called latent TB. If your immune system fails to destroy the bacteria Tb will infect the lungs first (pulmonary Tb) and then usually the glands that are part of the immune system. TB can also cause meningitis (inflammation of the membranes surrounding the brain and spinal cord), though this is very rare.
Where is tuberculosis most common in?
A graph showing the top ten countries suffering from non-HIV TB deaths. Eight of the countries located in Africa and the other two from Asia.
A graph showing the top ten countries suffering from non-HIV TB deaths. Eight of the countries located in Africa and the other two from Asia.
Most cases of TB occur in developing countries in Africa and South East Asia. In 2007and 2009 1.7 million people died from TB, the highest number of deaths in the African Region. But in the South-East Asia Region, 2008 accounted for 35% of incident cases globally. However, the estimated incidence rate in sub-Saharan Africa is nearly twice that of the South-East Asia Region with over 350 cases per 100 000 population.
What are the symptoms?
Depending on how effective your immune system is at fighting the infection, you may range from having no symptoms at all to symptoms that develop years after you were infected.
Most symptoms of tuberculosis are in your lungs they may include: * A persistent cough - containing phlegm and most likely blood. * Fevers * Feeling lethargic and tired. * Loss of appetite * Weight loss * A man suffering from the symptoms of TB.
A man suffering from the symptoms of TB.
Night sweats * Chest pain when you breathe in, caused by inflammation of the membranes lining your lungs (pleurisy)
Other Symptoms in your body: * Swollen glands in your neck. * Pains in your joints. * Bad Headaches.
How do you get it?
You catch TB by breathing in droplets in the air that contain the bacterium M. tuberculosis. These are spread through the air when someone with TB coughs or sneezes. Only some people with TB in their lungs are infectious to others.
Microscopic droplets of mycobacterium tuberculosis being spread into the air by sneezing.
Microscopic droplets of mycobacterium tuberculosis being spread into the air by sneezing.
Although it's spread through the air, you need to be closely exposed to a person with TB for some time before you catch it. People most commonly catch TB from people they live or work with.
Although TB, is quite difficult to catch in the UK you're more likely to get TB if you: * Have a weakened immune system (for example if you have HIV/AIDS or are taking medicines that suppress your immune system) * Have diabetes * Have regular close contact with people who have TB lung infection * Are very young or elderly * Live in overcrowded housing * Have an addiction with drugs or alcohol * Have very poor and have done for
The science behind TB
When the TB bacteria are inhaled into the lungs they are confronted by macrophages, immune cells that cleanse the body of invading pathogens or microbes. Macrophages are a type of immune cell which can kill microbes by a process called phagocytosis. Macro means "large" and phage comes from the Greek for "to eat”.
Macrophages recognize harmful substances in the body with antennae-like receptors and are usually the first to greet the unwelcome bacteria. The macrophage moves towards the bacterium and engulfs it in a pouch called a phagosome. The macrophage then "swallows" this pouch containing the microbe and fuses it with another vesicle called a lysosomes. In most cases, powerful digestive enzymes inside the lysosome then destroy the bacterium.
Macrophages engulfing a tuberculosis bacterium.
Macrophages engulfing a tuberculosis bacterium.
However, the TB bacterium has a mechanism that is able to alter the surface of the phagosome so that is cannot fuse with the lysosome. This leaves the bacterium alive and safe inside the macrophage where is able to grow and replicate. The bacterium eventually kills its host macrophage by reproducing many new bacteria that burst out of the macrophage. These new parasitic bacteria are then picked up by other macrophages which also become infected by them.
The damage caused to the lungs by a tuberculosis infection is actually caused by the body’s own immune system. As the bacteria kill macrophages, the lysosomes inside them release their powerful and toxic enzymes into the lungs. These chemicals eat away at the lung tissue and trigger an inflammatory reaction by the immune system, attracting other immune cells to the area and causing more tissue damage.
The attack by the TB bacteria on macrophages eventually triggers the production of immune system proteins called cytokines which increase the activity of macrophages and allows them to kill the TB bacteria. However, the hyperactive macrophages also cause further damage to lung tissue.
Tuberculosis may eventually be eliminated by the immune system or cause an on-going infection that results in a chronic inflammation of the lungs.
Can you cure it?
Antibiotics that are used to cure TB.
Antibiotics that are used to cure TB.
TB can be completely cured by taking antibiotics. Most people with either active or latent TB are treated with a combination of four antibiotic tablets for six months which will kill the bacteria. Treating latent TB prevents the infection from becoming active in the future.
You can also get a BCG (tuberculosis) vaccination which will inject a small amount of bacterium into your body not enough to cause any disease but enough for your body to produce antibodies that will fight and remember the bacteria. The vaccine is 70-80% effective against the most severe forms of TB.