What is tuberculosis?

Risa Bagwandin went to meet pathologist and world-renowned TB expert, Sebastian Lucas, surrounded by specimens from people who have fallen victim to TB at King’s College London’s Gordon Museum…

Sebastian - Tuberculosis is an infection caused by a bacterium called mycobacterium tuberculosis. It's a very common infection and we think about 10 million people a year globally fall ill from it, and it has a relatively high mortality. It has been with us for tens of thousands of years. Most people catch it by being breathed over by people who have got active tuberculosis, who are excreting the bacteria from their lungs. So every time they breathe out, tens, thousands, millions of tubercle bacilli come out and they're breathed in by another person and it goes into their lungs and starts the process of TB infection.

Risa - What are the symptoms if someone does contract tuberculosis?

Sebastian - It's estimated that if a hundred people get infected, 10 will develop disease. And the standard dogma is that half of those will get it within the first five years and the other half might get it later on in their life. The practical point is that a lot of people get infected by tuberculosis and they will have lesions in their lungs and in most cases those lesions will not progress. They will be evident on a chest x-ray later, but those people will not have actual disease. The small proportion of people who do develop active disease have an infection focus in the lungs, which enlarges and produces a mass, maybe the size of one's thumb or a little bit bigger, and the tubercle bacilli will then spread to the local lymph nodes and from there they may well spread through any other part of the body.

Risa - What are the first signs of someone that has tuberculosis?

Sebastian - It depends how severe the disease is. The majority of people acquiring tuberculosis for the first time will not know they've actually had it. I, for one, was infected around the early 1980s, but that only became evident when someone did a chest x-ray some years later and said, 'Oh, you've had old TB there'. And I said, 'Really? I was never ill'. And that's fairly typical, but if one is ill, the primary features are going to be cough. And then also the systemic features, if the infection spreads, of weight loss and just feeling ill. Coughing up blood comes a lot later, but basically cough that does not resolve is a very good clue that someone might have tuberculosis and if they have weight loss as well, that's a very good clue.

Risa - The initial symptoms are very similar to other diseases. For example, it could be confused with a common seasonal flu or bacteria that cause pneumonia. This makes it quite difficult for diagnosis to occur.

Sebastian - Absolutely. To prove tuberculosis properly, you have to see or identify the organisms. That can be done in a coughed up sputum and you can stain it and look under the microscope and see the tubercle bacilli. If a person therefore is symptomatic and they have demonstrated bacteria, then that is an absolutely classic definite case of tuberculosis. But a lot of people can have lung tuberculosis and one is unable to prove the organism because it is simply not there in large enough numbers to identify. The second thing is imaging chest x-rays and other sorts of chest imaging are very important in identifying tuberculosis. They will not prove that a lesion is tb, but there will be supportive evidence and as a result, certainly in high income countries, a lot of people will be treated as if they did have tuberculosis, but they may not because it was never provable.

Risa - In that case, if they have TB and we still haven't proved it, it means that they're also capable of transmitting it unknowingly.

Sebastian - That's an interesting question: Who transmits tuberculosis? We've been talking so far about people who have acquired tuberculosis for the first time, primary tuberculosis. Now primary tuberculosis does not generally destroy large areas of the lung. This point is important because if the lung is being destroyed, it generally means that you have an abscess cavity. Air now gets into those cavities and tubercle bacilli love growing in air, so there's a sudden very large rate of producing organisms that you can cough out. The practical point is that younger people don't produce these cavities. It's people who have tuberculosis generally later in life who have cavitated. They are the people who infect everyone else.

Risa - We're surrounded by specimens of previous TB patients. Can you give us a description of how disease progress in the body to actually cause the destruction that we see on the specimens?

Sebastian - Well, let's first look at this one, which is a lung slice. You can see a two centimeter white mass that is a tuberculoma, a massive caseating tuberculosis. This is a primary infection, so that's been breathed in and has produced the tubical focus there. It's spread a bit locally. It will also spread to the lymph nodes and here one can see from the lymph nodes that it's actually spread to other parts of the body because the rest of the lung has got these little tiny white spots. This is what we call miliary tuberculosis, Little tiny seeds of tuberculosis, which has come through the bloodstream via the lymph nodes. And this similar specimen here, which is a spleen from a child, is covered in little white miliary spots. So that child has had primary tuberculosis in the lung. It hasn't healed and is actually spread to other parts of the body. Kidney, liver, and bone marrow. Another place that tuberculosis can go to very readily is the brain. And here they've gone to the brain covering the meninges. These are the membranes around the brain and the spinal cord. And if you look at the base of the brain there, it looks rather murky because it's covered in an exudate of custardy material, which is tuberculous inflammation. You can see the whole spinal cord is covered in yellow, orangey material and that is a very severe example of tuberculous meningitis. The next specimen, we're looking at a lung here at which the upper part is completely destroyed. And you see these cavities, the important thing is the tub basc inside these cavities grow like mad, go into the bronch eye and being coughed up all the time. So that person with lungs like that until he died was chronically infecting other people all the time.

Risa - Is it possible that without being treated people actually die of tuberculosis?

Sebastian - In these cases, yes, because we know the dates when the specimens were acquired, which was before effective anti TB therapy came in, which is just after the second World war. And so these are historical examples of untreated tuberculosis. And the patient with the tuberculous meningitis divide of acute hydrocephalus, the patient with a cavitating tuberculosis here died of lung failure and the child with the splenic miliary tuberculosis, given that that will be affecting all other parts of his immune system, could well have died of immune failure. Now with therapy, you stop all that, the spleen can go back sort of to normal. The brain, the inflammation would certainly decrease and you may be able to rescue the patient. If you look at the destroyed cavitated lung TB therapy is not going to give you new lung tissue because it doesn't regrow. But if the damage has not been so severe, then that person can carry on living with, albeit reduced, lung function, but is still alive.