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Leprosy or Hansen's Disease Facts: Bacteria and Nerve Damage

Partial reabsorption of fingers in leprosy

Partial reabsorption of fingers in leprosy

A Potentially Serious Bacterial Infection

Leprosy is a disease that has been feared since ancient times due to its effects on the body. It’s caused by a bacterial infection and can produce debilitating and disfiguring symptoms. A lack of understanding of the disease has resulted in ostracism and sometimes cruel treatment of patients.

Doctors now know that it’s not easy to catch leprosy and that the disease progresses slowly. In addition, they can treat the infection effectively if it does develop. If someone becomes infected and doesn’t get treatment, however, serious nerve damage can result.

Leprosy is also known as Hansen's disease. In 1873, a Norwegian doctor named Gerhard Henrik Armauer Hansen discovered that a bacterium was the cause of the disease. The bacterium was eventually named Mycobacterium leprae. Though leprosy is the more common term for the illness, Hansen's disease is sometimes preferred today because it reduces the stigma attached to the illness. Some interesting discoveries have been made in relation to exactly how M. leprae causes nerve damage.

Mycobacterium leprae is the main cause of leprosy. The bacterium is stained red in this photo.

Mycobacterium leprae is the main cause of leprosy. The bacterium is stained red in this photo.

There are two main types of leprosy. Paucibacillary or tuberculoid leprosy is much milder than the multibacillary or lepromatous form of the disease. Some people have a disorder that is on the borderline between the two forms.

Possible Symptoms of Leprosy

The list below contains some common symptoms of leprosy. A patient may not have all of them. In addition, having one or more of the symptoms doesn't necessarily mean that a person has leprosy. Different diseases often share some of their symptoms. A doctor should be consulted if any of the listed problems appear or in any situation in which symptoms of ill health are severe, persistent, or recurrent.

The symptoms of leprosy take an average of five years to appear after the initial infection but may take as long as twenty years. The milder symptoms generally develop first. The disease is rarely fatal but may be so due to a secondary effect such as kidney failure. Symptoms may include:

  • skin lesions (patches with an altered appearance) that are white or red in color
  • numbness in the lesions due to nerve damage in the skin
  • skin lumps and bumps, especially on the face
  • loss of eyebrows and eyelashes
  • muscle weakness or paralysis
  • enlarged nerves under the skin that can often be seen from outside the body
  • eye and vision problems, including blindness in severe cases
  • nose problems, such as nosebleeds, a stuffy nose, and disfigurement
  • chronic ulcers on the soles of the feet
  • paralysis and clubbing of hands and feet
  • reabsorption of the cartilage in fingers or toes, making them shorter
  • damage to the male reproductive organs
  • kidney damage

Additional problems may develop because the patient may develop injuries in the areas without sensation. The nerve damage may stop them from feeling pain and realizing that their body is being hurt.

It's important to get treatment for leprosy as early as possible in the progression of the disease. The sooner treatment is begun, the less likely that symptoms will be severe or permanent. Early attention is necessary because doctors may be unable to correct some of the effects of the disease even when the bacteria are destroyed if treatment is delayed.

World Leprosy Day is held on the last Sunday of January. Its goal is to raise public awareness of the disease and to share facts about its nature and effects.

Transmission and Treatment of the Disease

Leprosy bacteria may be transmitted from person to person in droplets of moisture released when an infected person sneezes or coughs. Most people don't become infected when this happens, however. Long-term exposure to a contagious person is often needed in order to develop leprosy. In addition, a genetic susceptibility to the disease seems to be required. A regimen of specific antibiotics known as multidrug therapy is used to treat the illness.

A neuron with its axon surrounded by Schwann cells and a myelin sheath

A neuron with its axon surrounded by Schwann cells and a myelin sheath

Mycobacterium leprae and the Myelin Sheath

Mycobacterium leprae is a rod-shaped bacterium with rounded ends. It's a difficult organism to study because it's hard to grow in lab equipment and has little effect on most lab animals. This means that scientists don't know as much about its biology as might be expected. The bacterium affects the skin and the peripheral nerves (those leaving the brain or spinal cord and travelling to the surface of the body). In severe cases of leprosy, it may also cause damage to some of the internal organs.

Researchers have known for some time that the bacterial infection causes the myelin sheath around neurons to disappear. Myelin is a fatty material that electrically insulates the axon of a neuron, allowing the nerve impulse to travel effectively. A nerve impulse is a type of electrical current, although it consists of a flow of ions instead of the flow of electrons that occurs in a wire.

The myelin around the neurons in peripheral nerves is made by Schwann cells. These cells spiral around the axon of a neuron, wrapping it in layers of cell membrane containing myelin. Some evidence suggests that the leprosy bacteria enter the Schwann cells and interfere with their production of myelin. Other evidence suggests that the bacterium causes the immune system to attack myelin.

Mycobacterium lepromatosis also causes leprosy, although it appears to be a less common cause than M. leprae. It produces a distinct form of the disease found in Mexico. Some people have both species of bacteria in their body.

Genetic Reprogramming of Schwann Cells

In 2013, a group of researchers at the University of Edinburgh took Schwann cells from mice and added M. leprae to them. They found that the bacteria reprogrammed the cells by turning off genes used in mature Schwann cells and turning on ones used in immature ones. This reprogramming caused the cells to revert to an unspecialized form resembling that of a stem cell.

Stem cells are normally very useful because they can produce the specialized cells that we need when they are stimulated correctly. In the mouse experiment, however, the reprogrammed Schwann cells weren't useful because they were unable to make myelin.

The researchers placed the altered Schwann cells inside living mice. Some of the cells migrated to the muscles, carrying and distributing the bacteria as they travelled. This might be one way in which the bacteria spread through our body. Since humans and rodents are mammals, the results of experiments in mice often apply to humans. This is not always the case, though.

Mycobacterium leprae and Macrophages

In 2017, a team of researchers from the University of Cambridge found evidence suggesting that leprosy bacteria may cause myelin destruction by altering the action of the patient's immune system. They discovered that the bacteria enter white blood cells known as macrophages and hijack their activity. The scientists say that this leads to the injury to the nerves. Macrophages are part of our immune system. This system protects us from disease by destroying microbes that can make us sick and by removing and destroying damaged material.

Macrophages are large cells that engulf and digest particles in a process called phagocytosis. The particles that are "eaten" include bacteria such as M. leprae as well as unwanted material. Normally, bacteria that enter the macrophages are destroyed, but this may not happen in the case of the leprosy bacterium.

Four-day-old zebrafish; the lower one has been genetically modified to eliminate its dark pigment

Four-day-old zebrafish; the lower one has been genetically modified to eliminate its dark pigment

Zebrafish Research

The University of Cambridge researchers inserted leprosy bacteria into zebrafish larvae, which were transparent. The scientists had previously genetically modified the fish so that their myelin glowed a fluorescent green color. This enabled the scientists to more clearly see what was happening to the myelin. They then injected leprosy bacteria close to the myelin.

The researchers found that the bacteria appeared to settle on the nerve and that bubbles of myelin were released from the sheath. When the scientists examined their discovery in more detail, they found that the bacteria were located inside macrophages and that they were still intact.

The scientists say that it was actually the macrophages that damaged the myelin, not the bacteria. They confirmed this by destroying the macrophages in the zebrafish. The researchers found that the bacteria alone couldn't destroy the myelin. They also found that a molecule on the surface of the bacterium named PGL-1 altered the behavior of the macrophages, causing them to make an excessive amount of nitric oxide. This chemical damaged the mitochondria of the nerve cells. Mitochondria produce energy for a cell. If a cell contains an insufficient number of mitochondria, it can't survive.

The researchers say that the altered macrophage damages neurons in two ways: it damages the nerve cells directly and it stops "patrolling" the neuron to protect it from damage.

The Potential Importance of the Research

Both the 2013 and the 2017 reports about M. leprae are very interesting, but as far as I know each study has been performed by only one group of researchers. This doesn't mean that the results are incorrect, but results from another team could add evidence supporting the original study. One or both of the discoveries might be medically useful if they are correct.

A problem with the first study is that the bacterium's behavior in mouse cells and living mice may not be the same as its behavior inside our body. A problem with the second one is that discoveries in zebrafish larvae may not apply to humans. It's interesting to note that the fish have been useful in the study of an M. lepae relative called Mycobacterium tuberculosis, however. As its name suggests, this bacterium causes tuberculosis. In addition, the biology of zebrafish larvae has important similarities to that of mammals, including humans.

Both sets of researchers hope that that their discovery will help treat leprosy in some way. The 2013 researchers hope that leprosy can be diagnosed at an earlier stage. The 2017 researchers hope that nerve damage caused by the bacterium can be reversed. Both sets of researchers suspect that their research will lead to a better understanding and perhaps a better treatment for other demyelination disorders, including multiple sclerosis, or MS. In MS, the immune system is believed to destroy the myelin around nerves. It would be wonderful if more recent research improves our understanding and treatment of multiple diseases.

Leprosy is uncommon in the United States, but it does occur in the country. The CDC says that around 150 to 250 cases of the disease are diagnosed in the USA each year.

Leprosy in the Present and the Future

The World Health Organization (WHO) reports that the incidence of leprosy is decreasing. Some health experts believe that certain countries are becoming complacent with respect to the disease and that far more cases exist than are being reported. This is very troubling because the illness can be treated and the worst of the permanent effects avoided. If people aren't identified as having leprosy, they won't be given the appropriate antibiotics and may develop life-altering symptoms that could have been prevented.

People with leprosy were treated badly in the past. Unfortunately, they still are in some countries. Education of the public is important. Better treatment for the effects of the illness would be wonderful. It's good that we can destroy the bacteria in some patients. Depending on when the treatment is started, however, the bacterial infection may cause disabling and irreversible effects. I hope that recent and new research prevents this from happening.


  • "Hansen's Disease (Leprosy)" from the Centers for Disease Control and Prevention, or the CDC
  • "Leprosy Overview" from WebMD
  • Facts about leprosy from the Merck Manual
  • "Leprosy Reprograms Body's Cells" from the American Association for the Advancement of Science
  • "Leprosy turns the immune system against itself, study finds" from the Medical Xpress news service
  • Mycobacterium lepromatosis information from the Wiley Online Library (Abstract)
  • "Leprosy" from the World Health Organization, or WHO
  • "Shadow of leprosy falls again as experts claim millions of cases go undiagnosed" from The Guardian

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: Has Hansen's disease been found in the U.S? Where is it most commonly found?

Answer: Yes, it has. The CDC’s website about Hansen’s disease says that around 150 people in the United States get the illness each year. The website also says that early diagnosis and treatment for the required length of time can cure the disease. The illness mostly appears in the southern part of the United States. The HRSA (Health Resources and Services Administration) website in the link below lists the states where most of the cases have appeared.

© 2017 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on April 23, 2020:

I hope that the disease can be totally eradicated, too. It's sad that anyone has to suffer from it.

I'm well at the moment. I hope you are, too, Patricia. I appreciate the Angels very much. Blessings to you.

Patricia Scott from North Central Florida on April 23, 2020:

I recall many years ago hearing about lepers and their ill treatment. I do hope it can one day be totally eradicated. Hoping you are well and safe...many Angels ar headed your way. ps

Linda Crampton (author) from British Columbia, Canada on April 23, 2020:

Hi, Peggy. Yes, it is believed that armadillos picked up the leprosy bacterium from humans. Unfortunately, I've read that in some instances they may be passing it back to us. Thanks for the comment. I always appreciate your visits.

Peggy Woods from Houston, Texas on April 22, 2020:

I remember reading that those who had leprosy used to be shunned and were sent to leper colonies. It is a shame that the diagnosis cannot be made earlier before damage is done since it is so easily cured with antibiotics.

It is also interesting that humans passed leprosy on to armadillos...not the reverse as is often the case. As always, your posts are so informative!

Linda Crampton (author) from British Columbia, Canada on February 11, 2018:

Hi, Yves. Thanks for the visit. Unfortunately, people generally don't visit a doctor until symptoms become apparent. It would be great if the disease could be diagnosed before symptoms appear.

savvydating on February 11, 2018:

Hello Linda...Quite an impressive article. I had no idea that leprosy is relatively easy to cure. Still, it is too bad it takes so long(up to 20 years) to become apparent on an individuals body. Consequently, I do wonder how the disease might be caught early. (Maybe I missed that part.)

At any rate, I am glad to know that leprosy is rare and that it can be treated.

Linda Crampton (author) from British Columbia, Canada on January 09, 2018:

Hi, Nell. Leprosy is an interesting disorder, though it can be sad for the people who get it. Thanks for the visit.

Nell Rose from England on January 09, 2018:

Fascinating. I have always had a rather macabre interest in leprosy, I have no idea why! I do remember reading about an Island somewhere, maybe near Italy? Especially made for lepers. Can't remember exactly where. Using the Zebra fish was pretty clever too!

Linda Crampton (author) from British Columbia, Canada on October 28, 2017:

That sounds like a difficult problem for your workmate, Colin. It must be hard for him to avoid injuries. Thank you for the visit.

colin powell from march on October 28, 2017:

That was interesting. Leprosy is a disease I've heard of. It was once common in Europe. But I think that was in the Middle Ages. I don't believe it has been in Britain for some time. Some of the symptoms you mentioned. The sores on the feet and the nerve endings not feeling pain. One of my workmates has this, but it was brought on by diabetes. He can't feel the pain in his feet even though they blister and bleed.

Linda Crampton (author) from British Columbia, Canada on September 15, 2017:

Thank you for the comment, Dianna. I appreciate your visit.

Dianna Mendez on September 15, 2017:

I did not realize this disease was throughout the world. As always, your posts are interesting and give readers much to consider.

Linda Crampton (author) from British Columbia, Canada on September 09, 2017:

Thanks for the kind comment, DDE.

DDE on September 09, 2017:

Informative and so much to learn from the interesting topic. You certainly researched in detail.

Linda Crampton (author) from British Columbia, Canada on September 04, 2017:

Thank you very much, Nadine. I've never heard of the film that you mention. I'll have to look for it.

Nadine May from Cape Town, Western Cape, South Africa on September 04, 2017:

Wow, Linda, you must have done a lot of research to write this informative article. People with leprosy were totally isolated in the film City of Joy. Glad that today it can be controlled or even cured.

Linda Crampton (author) from British Columbia, Canada on September 03, 2017:

Hi, Martie. Yes, the advances and discoveries in medicine are exciting. I hope they lead to better treatments for disease as soon as possible.

Martie Coetser from South Africa on September 03, 2017:

Oh, leprosy was such a traumatic and devastating disease for ages before medical science discovered a treatment. We are living in a wonderful time.

Thanks for this informative and useful hub, Linda!

Linda Crampton (author) from British Columbia, Canada on August 31, 2017:

Thanks, Louise. I appreciate your visit.

Louise Powles from Norfolk, England on August 31, 2017:

Yes I agree with Larry, this was very educational to read. Although I've heard of Leprosy, I knew very little about it.

Linda Crampton (author) from British Columbia, Canada on August 30, 2017:

Hi, Sonia. Yes, there has been a lot of dread attached to the disease. There does seem to be more understanding of the disease and of the people who have it, although this isn't the case everywhere. I hope the illness is eradicated soon.

Sonia Sylart from UK on August 30, 2017:

Leprosy is a word/disease I have not heard about in a long time and from what I had heard of this disorder, the words alienation, fear and dread come to mind. It is good to learn from this thoughtful article that things are changing for the better for those who unfortunately have this condition, and that there is more understanding generally.

Linda Crampton (author) from British Columbia, Canada on August 27, 2017:

Thank you, Larry. As always, I appreciate your visit.

Larry Rankin from Oklahoma on August 27, 2017:

Always educational.

Linda Crampton (author) from British Columbia, Canada on August 27, 2017:

Thanks for sharing the interesting information, Jackie. I hope scientists investigate the composition and effects of bee venom. It sounds like it might be a useful substance.

Jackie Lynnley from the beautiful south on August 27, 2017:

This is a great article Linda with so much information. My best friend from high school died from MS and if I had know about her disease before she died I would have encouraged her to use bee serum to help her. I think they over look this treatment that many live by and claim to be cured from that could help in all this maybe. It certainly worth investigation and it really makes me mad how so many of them poo poo it, especially since I had arthritis in my ankles so bad in my thirties I could barely walk but got accidentally got stung multiple times not by the recommended bees but hornets and it cured me.

I know it is somewhat changing the subject but since this may be linked to MS the cure may be too and I have waited so many years to see them look into this with no luck. It really is so disappointing.

Linda Crampton (author) from British Columbia, Canada on August 27, 2017:

Hi, Dora. Unfortunately, the disease still exists. I hope there isn't a resurgence of leprosy. I'm glad that the bacterium that causes the disease might help us learn about other illnesses, though.

Dora Weithers from The Caribbean on August 27, 2017:

Really, I had almost forgotten about the disease. I am told that there used to be a leprosy ward in the hospital on this island many, many years ago, then it closed because there were no more patients. Thanks for the up to date information.

Linda Crampton (author) from British Columbia, Canada on August 26, 2017:

Thanks for the comment and for sharing the information, Besarien. The case of animal cruelty sounds horrible. I'm glad it was discovered.

Besarien from South Florida on August 26, 2017:

Fascinating hub! You did an excellent job of making a complex topic easier to grasp. I was especially interested in what leprosy might teach us about reprogramming Schwann cells or other cells for that matter to act like stem cells, and also how better to combat other demyelination disorders.

Also, there was a case in Florida, about a year ago, where a farm was shut down for animal cruelty. It was suspected amongst a litany of other evils, that they were selling armadillo meat as something else entirely, possibly to restaurants.

Linda Crampton (author) from British Columbia, Canada on August 26, 2017:

Thank you very much, Chitrangada Sharan. I hope we win the battle against leprosy. It can sometimes be a horrible illness if it's not treated.

Chitrangada Sharan from New Delhi, India on August 26, 2017:

This is an excellent article about Leprosy ! Such a scary disease ! You have provided almost all the information about it to creat awareness among people. It's heartening to know that the occurrence of this disease is decreasing in general.

Thanks for sharing another of your well researched and educative article!

Linda Crampton (author) from British Columbia, Canada on August 26, 2017:

Thanks, Bill. I'm hoping that the research will help us to understand MS and other diseases involving loss of myelin. We need a breakthrough in this area.

Bill Holland from Olympia, WA on August 26, 2017:

Absolutely fascinating information, Linda! I have several friends with MS, so hopefully understanding of that disease and a cure will follow soon.

Linda Crampton (author) from British Columbia, Canada on August 26, 2017:

Hi, Flourish. I hope the full details of how MS develops are discovered soon and that this leads to a cure or at least better treatments. Thank you for the visit.

FlourishAnyway from USA on August 26, 2017:

Fascinating, especially the analogous connections to MS which I hav a sneaking suspicion is at least in part bacterial but we just don't know enough. Hansen's disease is so devastating.