Question: What are the symptoms of TB and how does it infect people

Matt Bilton answered on 13 Nov 2014:

Great question! When someone is sick with TB (so not just infected), there are often plenty of bacteria growing in lungs where there is tissue damage caused by the disease. When someone in this state coughs, bacteria contained within aerosol droplets can be propelled into the air. If someone lives in close contact with a TB sufferer like this, they can inhale these droplets.

Once inhaled, the bacteria most likely land on the epithelium lining the airways. Alveolar macrophages – professional pathogen eating cells that live in the lungs – are pretty close by, and so they hunt out the bacteria and try to eat them. Unfortunately TB bacteria have a few tricks up their sleeve and in certain circumstances can live very happily inside the unsuspecting macrophage. This can lead to a bit of a standoff. On the one hand, the macrophages try and kill and digest the bacteria; on the other, the bacteria do their best to grind this to a halt.

If the macrophages fail to control the bacteria, other white blood cells can offer a hand, either attacking the bugs directly, or by helping infected macrophages to defeat their assailants themselves. The recruitment of these additional cells to the site of infection leads to everything coming together around the bacteria forming lesion called a granuloma – a hallmark characteristic of tuberculosis.

If a granuloma forms like this around live TB bacteria, the bacteria may enter a sleeping state, and they can remain like this for many years. Sometimes, the bacteria can reawaken – this is especially likely if the immune system is weakened following infection by another pathogen – say for example, HIV. This can lead to reactivation of disease, allowing the cycle of infection to continue to the next victim!

If and when they reawaken, the TB bacteria can spread to different parts of the body – so not just the lungs – and the symptoms can depend on where in the body the bacteria are. General symptoms of TB can be weakness and fatigue, weight loss and fever/chills, whilst more location specific symptoms can be a bad cough that won’t go away and/or coughing up blood and sputum in the case of bacteria in your lungs, or swollen lymph nodes, easy to break bones or even diarrhoea in the case of bacteria which have spread to the lymph nodes, bones or intestines!

For more information on the symptoms of TB, you can check out the NHS Choices website here which addresses this quite well: http://tinyurl.com/TB-symptoms-NHS