Science Interviews

Interview

Sun, 30th Jan 2011

Leprosy in the World Today

Professor Diana Lockwood from the London School of Hygiene and Tropical Medicine

Listen Now    Download as mp3 from the show Leprosy: The Low Down

Ben -   Leprosy is caused by an infection of Mycobacterium bacteria, the same family as the pathogens that cause TB.  Most people here in the UK think of leprosy as a medieval disease, one long-since wiped out, but sadly, that's not the case.  Leprosy still affects people worldwide and Professor Diana Lockwood from the London School of Hygiene and Tropical Medicine joins us now to tell us more. 

Thank you very much for joining us, Diana.  I wonder if you could start by telling us, how big a problem is leprosy today?

A photomicrograph of Mycobacterium leprae taken from a leprosy skin lesionDiana L. -   Leprosy is a very big and important problem.  About 250,000 new cases are detected worldwide each year and that number is pretty stable at the moment.  So that means that we’ve got a lot of new people coming in and the risk is that they will also develop disabilities that we associate with leprosy, and that will add to the number of leprosy cases that are around.

Ben -   Where in the world do we actually find it?  Is it like other diseases that we think are medieval and wiped out?  I know that things like the plague are actually still around in certain parts of the world.  Is it just hanging on in certain pockets or is it spreading around the world still?

Diana L. -   60% of the world’s cases are in India and India is certainly the hotspot, and Northern India has more cases than anywhere else.  Rather surprisingly, Brazil is the next most endemic country and particularly in Northern Brazil, again, associated with poverty.  So Brazil has about 11% of the world’s cases, but all through Africa, places like Ethiopia, Nigeria, Mozambique, Madagascar, these all have large numbers of new leprosy cases each year.

Ben -   How is it actually transmitted from one person to the next?

Diana L. -   What happens is that a very small proportion of people with leprosy are infectious.  I want to emphasise that because you don't get leprosy from touching somebody and what happens is that the small number of people who are infectious cough and sneeze the leprosy germ out into the environment.  It’s a very hardy germ and it can survive in the environment for up to a month.  Then people breathe it in, and most people who breathe the leprosy germ in then mount protective immune response to it.  So, I've worked with leprosy in India and Ethiopia, and I've obviously met the leprosy germ many times and so I've presumably, although I've not tested myself, developed protective immunity to it.  And that's what most people who live in leprosy endemic countries do.

Ben -   So, it gets into our system through the lungs, but what does it actually do to the body once this bacterium is in there?  What does it do?

Diana L. -   Well, there are two critical things.  Firstly, it has a receptor to bind to the nasal mucosa that crosses the nasal mucosa and then it binds to macrophages and also to Schwann cells in peripheral nerves.  That's important because that's how you get the clinical signs of leprosy.

Ben -   Schwann cells are the cells that actually make the protective coating for our nerves, aren’t they?  So if they're binding to these cells, they're stopping our nerves from being protected properly and our nerves will therefore break down.

24 year old man from Norway, suffering from leprosyDiana L. -   That's right, yes and so, one of the very important signs of leprosy is loss of nerve function which is manifest as either losing sensation in your hands and feet, or losing power in your hands and feet.  People have this idea that leprosy eats away your body, but it doesn’t actually eat away your body, what happens is that you lose pain sensation in your hands and feet, and then you don't feel injuries, and so, you get what we call traumatic injuries.

Ben -   So, the stereotype that leprosy causes your fingers to drop off is not actually because your fingers drop off as a direct result of the presence of the bacteria, but because you injure your fingers so often because you don't feel the pain there any more, that you're quite likely to lose fingers, toes, and other extremities through that mechanism.

Diana L. -   Yes, that's right and so, when you diagnose a new patient with leprosy, it’s really important that you do a careful examination to find out if they've got undetected loss of sensation in their hands and feet, and then institute a kind of health education programme with them, which obviously will be very much guided by the kind of activities that that person does.  So, for instance if you're a farmer in Africa, you might be at risk by walking too far or holding your hoe too tightly; but if you're an Indian housewife, your danger area is the kitchen, and it’s very easy to burn yourself in the kitchen.

Ben -   So, how is it actually treated?  Can we use standard antibiotics?

Diana L. -   Yes, we’ve got very good antibiotics for treating leprosy and the key is a drug called rifampicin and every patient with leprosy will get a combination of either two or three drugs, antibiotics against leprosy, and they will take them for either 6 or 12 months.  The beauty of the rifampicin is that you only have to take it once a month because, again, the Mycobacterium leprae is a very slow growing organism and so fortunately, we only have to take the rifampicin, once a month.  The other antibiotics you have to take every day.

Ben -   Is this a cure for leprosy or is it merely a case of, once you've contracted it, we have drugs that can manage it, and you get to end up with these drugs for the rest of your life?

Diana L. -   No. It cures you of the infection.  What it doesn’t cure you of is the inflammation that goes with this. We talked about the Mycobacterium going to the Schwann cells and the skin macrophages, and what happens then is that the body then mounts an inflammatory response.  That is far more difficult to switch off and that can go on for a long time.  So, patients will quite often need to have a course of steroids along with their antibiotics to try and switch off that inflammation because it’s that inflammation that's destroying the nerves.

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