Leprosy, Hansen's Disease


Leprosy lives in historical tales and Bible stories. It's an ancient disease that created fear and stigma. It's a disease that exists today.  It continues to infect people around the world, though much fewer, in areas where medical care has been slower to stamp out this curable disease.

What causes leprosy?

Leprosy is caused by bacteria - Mycobacteria leprae (as well as newly identified bacteria called Mycobacteria lepromatous).

It is a slow growing bacteria. Symptoms may not begin for 2-10 years.

It is thought that most people - 95% in fact - are immune. Only a small number of people have the genes that make them susceptible to Leprosy.

How many are infected?

There were around 180,000 chronic and 215,000 new cases in 2014. There were however over 5 million chronic cases in the 1980s. Over 15 million have been cured since multidrug treatment began in the 1980s.  About 2 million are permanently disfigured or disabled as a result of past disease.

The WHO has targeted Leprosy for elimination from countries where it continues to spread.

What does it cause?


Leprosy particularly affects the skin, mucous membranes, and nerves. For some, this causes the skin to become numb and lose color; for others, this causes disfiguration, loss of fingers, and pain and weakness.

There are different types of Leprosy.

Some with Leprosy have Paucibacillary disease with a few light colored skin lesions without sensation.

Some have just one lesion.

More serious disease is seen with Multibacillary disease (MB). This is the classic disease recorded in history.

Some effects in Multibacillary disease can be disfiguring, including:

Skin color fading or discolored

Skin growths and nodules/bumps

Thick, stiff, or dry skin


Effects of Multibacillary disease are also on nerves, causing:



Muscle weakness

Paralysis especially of hands and feet

Vision Loss, Blindness

Enlarged nerves

Additional effects of  MB disease on mucous membranes can lead to:

stuffy nose

nose bleed

Loss of sensation in hands and feet can lead to accidents and further problems.

Some may also lose fingers and toes.

The differentiation of these types of Leprosy can be made from a skin biopsy. In reality, there are often not skin-smear services available where Leprosy is. Instead, classification is by examining the patient and noting how many lesions and nerves are affected.

What happens next?

Most cases of leprosy  - even without any treatment - will cure spontaneously, especially the tuberculoid and indeterminate types.

There is, however, treatment.

The first treatment - dapsone -was started in 1945, but resistance developed and the response was imperfect. In 1981, multidrug treatment was started. Treatment drugs are free for all with Leprosy from the WHO. However, many patients exhaust finances paying for costs for medical appointments, transport, radiologic imaging and other tests.

For Multibacillary (MB), treatment is usually for 1 year often with Rifampicin, Dapsone, Clofazimine (some meds daily, some once a month). For Paucibacillary (PB). dapsone and rifampicin for 6 months (again mixed daily/monthly dosing). For a single lesion: a single dose of Rifampicin, Ofloxacin, Minocycline.

How does it spread?

Leprosy is sometimes called the "least contagious of contagious diseases".

The interesting thing is we still don't know exactly how a disease known for several millennia spreads.

The bacteria spreads from person-to-person. Short casual contact does not seem to risk spread. It appears to spread to those few who are susceptible through a cough or sneeze, leading to droplets - maybe from mucous membranes in the nose or mouth/throat - landing on another's mucous membranes in the nose, mouth, or throat. These secretions and droplets do contain the bacteria.

It is rare for transmission to occur after exposures. So it has been difficult to identify how this happens.

Really armadillos?

Yes. Cases in the US have been traced back to contact with armadillos. So don't touch armadillos.

Armadillos are the only animal - besides other people - that is known to spread leprosy.

Where is Leprosy found?

Leprosy occurs around the world. Most cases are limited to a handful of countries: Angola, Brazil, the Central African Republic, India, Madagascar, Nepal, and Tanzania as well as the Democratic Republic of the Congo and Mozambique. These are countries that have over 1 in 10,000 infected. Most cases (over 50%) occur in India. The US has about 200 a year.

What sort of bacteria causes leprosy?

The bacteria causing Leprosy is a Mycobacteria, which makes it a relative of Tuberculosis.

How is it diagnosed?

A skin biopsy is usually used, if available. Diagnosis is sometimes based on clinical presentation alone. Some blood tests for antibodies are used, but not in the US as the tests do not provide clear results.

Isn't this called Hansen's Disease?

Yes, Leprosy is also called Hansen's Disease. Many prefer this term because it avoids the stigma associated with leper or accordingly with leprosy. Historically, many were shunned from their communities or families for having this disease. or having the disease and historically thought to be at fault or be morally impure.

However, the history of the name Hansen's Disease is itself painful. Dr. Gerhard Hansen hypothesized that leprosy was an infectious disease (even though his father-in-law seemed to show it was not and that it simply ran in families). He was able to identify the bacteria under a microscope. He then inoculated a woman's eye with material containing this bacteria using a small knife without her permission. (The infection did not take and she already had leprosy, actually). 

The Norwegian government, appropriately, was not in favor of Hansen's experimentation without permission. Hansen went on trial for this experiment. He lost his position leading the leprosy hospital but remained the chief medical officer for leprosy in Norway.

Hansen's discovery was the first discovery of a bacteria causing human disease - back in 1873. Subsequent isolation of patients due to the knowledge that it was infectious lead to the elimination of the disease in the 1920s in Norway

It should be noted that Hansen's father-in-law was partially right. Because leprosy is a disease that spreads through close proximity and prolonged exposure among those few with the genetic risk, leprosy does indeed spread among families, even though it is infectious.

Any more history?

Leprosy has been seen - and it's quite visibly seen - in humans since the beginning of recorded history. The ancient Egyptians, scholars in India, and Alexander the Great's armies reported leprosy.

Historically, Leprosy was a problem for Europe in the Middle Ages, especially the 12th and 13th centuries, but then receded, without any treatment or apparent directed public health measures. At the same time, the disease remained in the Middle East, Asia, and Africa. Despite leprosy receding from Europe, it did remain in Norway, where it had the highest concentration in Europe, and where Hansen faced it. 

Around the world, there were Leprosy sanatoriums - from Louisiana to Hawaii to Japan to India. Isolation of patients who were infectious - though only minimally - did help prevent the spread of the disease.

There wasn't treatment developed until the late 1940s - dapsone. However, strains resistant to dapsone quickly appeared. Later in the 1980s, multidrug treatment had a sizable effect on the disease spread. Cases dropped dramatically around the world.

Can pets get it?

No, unless you have an armadillo. Actually, mice are used as lab animals for the study of the disease. They can be infected with inoculation into their foot pads.

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