Leprosy – How the leper got its spots

Oh crap, I forgot about World Leprosy day (celebrated on January 31st or the closest Sunday). Quick! Read this old article on leprosy that I wrote for On Dit.

Leprosy is a disease wherein the slightest tug to a limb will tear it off like a well-cooked chicken. It is also highly contagious; such that simply touching a person with leprosy will infect you and will certainly and very shortly cause your arms and legs to fall off. *SLAP!* You useless child! *SLAP!* You know nothing about leprosy! Now before I lock you in the basement, I’ll straighten you out…


Ahhh! Is it catching? (Photo by Thomas Tu)

Leprosy is caused by the bacterium Mycobacterium leprae. (Funky fact: In 1873, M. leprae was the first human-disease-causing bacterium to be identified!) Depending on the strength of immune response incited after infection, one of two types of leprosy may be experienced: tuberculoid, which tends to produce more nerve damage; or lepromatous, which manifests itself in a more skin-oriented way. Don’t be fooled, leprosy is not an insignificant disease, leprosy infected an estimated 410 000 people worldwide in 2004, 75% of whom lived in the poorer countries of Africa, Asia and Latin America.

It is rather difficult to transmit leprosy. A specific mechanism of transmission hasn’t been found, but studies have shown that sneeze droplets from long term sufferers may be a significant route. However, only people with continuous exposure to these droplets are likely to be infected. The bacteria in the droplets were observed to be viable after 9 days outside the body, so infected linens or clothes may also be a factor. Reservoirs of the bacterium also exist in nine-banded armadillos [due to their strangely low body temperature (explained later)], but they don’t play a role in transmission to humans.

After exposure, there is a stupidly long incubation period of six months to fifty years before any symptoms may surface. This is due to the M. leprae’s extremely long generation time (the time it takes for a colony of bacteria to double) of two weeks. In comparison, it replicates about 1 000 times slower than E. coli, which replicates on average every 20 minutes.

Once it infects the host, M. leprae burrows itself into host cells to hide from the immune system. It usually finds the specialised cells that surround and insulate neurons, called Schwann cells, or white blood cells to live in. Eventually, a decolourised or reddened blotch appears on the skin surface. 75% of infected people have strong enough immune responses against the bacterium that the patch goes away by itself and they are unbothered by the disease.

If their immune system sucks, the patient is likely to develop tuberculoid leprosy. This is when the body, in absence of a proper immune response, launches a type of allergic reaction against the nerve sheaths that contain the bacteria. In this non-progressive (it doesn’t get any worse over time) form, only a single hypo-pigmented (not coloured) patch of skin appears. This patch usually loses its hair, sweat glands and other skin organs.

Significant damage to the nerves also occurs, especially to the ones leading to the extremities and the ears. This causes first insensitivity to extremes in temperature, then inability to feel light pressure, pain and finally deep pressure in the affected area. The loss of function is permanent, even if the leprosy is treated. The nerve damage also causes atrophy (wasting away due to non-use) in the affected limb. If the patient is not careful, little nicks and cuts on affected limbs can be opened up unintentionally, since they can’t feel pain. These sores can then become aggravated, infected and may require amputation of the affected area.

However, if their immune system really sucks and doesn’t even launch an allergic response against M. leprae, the infected patient may develop a case of lepromatous leprosy. This form causes discoloured patches, nodules and sores all over the body. These preferentially gather at the cooler areas of the body (such as the toes, fingers, face and testicles) because the optimum growth temperature for the bacterium is around 27 – 30°C, significantly lower than normal body temperature. Further disfigurement happens as body hair follicles die, starting from the eyebrows downwards. Nerves are also damaged in this form, but not to the extent of tuberculoid leprosy.

This is the only version of leprosy where large amounts of bacteria replicate in the host, so it’s thought that it is the only infectious form.

Treatment used to be limited to a single antibiotic called dapsone. But after some medical research and observations that the bacteria were building up a resistance to it, treatment was replaced with multi-drug therapy, a combination of three different antibiotics. This cures the disease and reverses many of the disfiguring nodules, but not the nerve damage. No real prevention is required as long as symptoms are recognised early and treated quickly, due to incredibly slow nature of the disease. Also, a relatively successful vaccine has been found for its prevention.

Even though treatment is free from the World Health Organisation (or the WHO, named so that many a hilarious Abbot and Costello skit can be performed by everyone, healthy and sick alike) and the disease readily diagnosable, people are still letting the disease go into the debilitating late stages. Due to the societal ostracising of lepers (justified by tradition, passed down from generation to generation from biblical times), people are hesitant to come forward and be branded a leper. Combating stupid human behaviour like this is the main focus of stopping disease outbreaks, not miracle drug cures. Medicines are useless if people don’t take them.





Filed under Thomas' Corner

2 responses to “Leprosy – How the leper got its spots

  1. I enjoyed reading this article, though having breakfast at the same time was probably a mistake. I’m pretty grossed out right now.

  2. Interesting- odd how it isn’t known definitely how the Mycobacterium colonises the human body, how it is still passed on in large numbers each year and how it is actually endemic in two states of the USA! [Louisiana and Texas] I can remember as a kid living in NSW, how the Baptist missionary groups used to come asking for donations once a year so that Pacific Island people could receive antibiotic treatment for leprosy. I understood it then as a disease that made people numb and then pieces of them fell off- sounded frightening!
    When I read that leprosy was first identified as a distinct disease with a probable microbial cause by a Norwegian doctor working in Norway (1873 I think), I was really puzzled. Along with the majority of people, I thought it was a tropical disease, but apparently it is widespread over hot to cold countries. Lower SES and poor nutrition accompanied by crowded housing provide ideal conditions for leprosy as for other bacterial diseases. When I was in Norway several years ago I visited the now closed St Jorgen’s Hospital for Hansenians in Bergen. This was full of lepers for many years and they had to look after themselves in there, with food and medicines passed to them by carers through the gates, rather than having attendants nursing them. Interestingly, leprosy disappeared quite quickly from Norway when large numbers of young men emigrated to the USA from the 1890s onwards. Nowadays Norway doesn’t have endemic leprosy but Northern Japan does! I think there is still a lot to learn about this perennial disease.

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