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Yaws Disease: Causal Bacterium, Symptoms, and Treatment

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

What Is Yaws?

Yaws is a chronic disease that affects the skin, bones, cartilage, and joints. Though it’s rarely fatal, it may have a major effect on quality of life by causing disfigurement, disability, and pain. In 2012, a doctor discovered that a single dose of an inexpensive, orally-administered antibiotic could cure the disease. This has led to the hope that it can eventually be eradicated. Unfortunately, the disease still exists and is still causing problems.

The disease is caused by a spirochete bacterium called Treponema pallidum pertenue. The spirochete (or spirochaete) belongs to the same species but a different subspecies of the bacterium that causes syphilis. Yaws is not a venereal disease, however. The effects of the two subspecies in our body are very different, but apart from this fact they are hard to distinguish from one another.

There are 15 countries currently known to be endemic for yaws.

— World Health Organization (2022 report)

Endoflagella or axial filaments of a spirochete

Endoflagella or axial filaments of a spirochete

Features of Spirochetes

Spirochetes are microscopic, one-celled organisms belonging to the phylum of the same name. Members of the phylum cause a variety of human and animal diseases, including Lyme disease, leptospirosis, syphilis, and yaws. The bacteria in the phylum often have a helical shape and move by means of flagella. Treponema survives by absorbing chemicals that it encounters in our body. It uses these chemicals as nutrients.

The flagellum of most bacteria is a long, whip-like structure that is attached to one end of the cell and extends into the liquid medium surrounding it. The flagellum rotates and propels the cell through the liquid as it does so. The rotation is driven by a structure called the flagellar motor, which is located at the base of the flagellum inside the bacterium. Not all bacteria have a flagellum. On the other hand, some species have multiple flagella.

The cell of a spirochete is enclosed by two membranes. These have a space between them called the periplasm, which contains a thin gel. The flagella of spirochetes are enclosed within the periplasm instead of extending into the surrounding medium. They are sometimes known as axial filaments.

The rotation of the flagella within the periplasm allows the cell to move through a wide variety of environments. This ability is helpful for the bacterium when it's travelling through our body. It's able to move through a viscous medium such as the one located in our connective tissue, for example. The movement of each flagellum is controlled by a motor, as in other bacterial cells.

The Subspecies of Treponema pallidum

Three subspecies of Treponema pallidum affect humans: T. p. pallidum (whose name is also written as T. p. ssp. pallidum), T. p. pertenue, and T. p. endemicum. The first bacterium causes syphilis, which is generally venereal, or sexually transmitted. The bacterium is very invasive, produces a wide range of symptoms, and is sometimes dangerous. T. p. endemicum causes a disease called bejel or endemic syphilis. Despite the word "syphilis" in its alternate name, it's not a venereal disease. Like T. p. pertenue, it affects the skin and bones, though it causes different symptoms. It doesn't cause a deadly infection.

Although the three subspecies of T. pallidum cause different effects in our body, they look identical. They also produce the same results when serological tests are performed. A serological test is a blood test that looks for specific antibodies. Another similarity is that the three bacteria affect the body in stages (primary, secondary, and tertiary).

Treponema carateum causes a skin disease called pinta. At the moment, it's classified in its own species. Although genetic tests haven't yet been done to prove that it's a subspecies of T. pallidum, researchers strongly suspect that it is. It produces the mildest disease of the four bacteria and affects only the skin.

Whole-genome sequencing has demonstrated that the genome of T. p ssp. pertenue differs by only 0.2% from that of T. p ssp. pallidum.

— Marks et al, British Medical Bulletin

Possible Symptoms of Yaws

Yaws almost always occurs in tropical areas. The origin of its name is unknown. There may be three stages in the untreated disease, as described below. Only a doctor can diagnose the cause of the symptoms that are listed, which may not be due to yaws. Skin ulcers can be caused by a variety of factors, for example.

A major problem with the yaws bacterium is that it can produce a latent infection. In this stage of the disease, the patient seems to be well. The bacterium is still alive in their body, although it's inactive. At some point in time, it may become active and cause symptoms.

Initial Presentation

The first symptom of yaws is a papilloma (a benign tumour) in the skin. The papilloma is loaded with bacteria and sometimes releases an exudate. It's often known as the mother yaw. The legs are a common site for the mother yaw. The papilloma may eventually form an ulcer, or an open sore. It sometimes heals on its own, leaving a scar.

Secondary Symptoms

Other symptoms may appear while the mother yaw exists or weeks or even months after it has disappeared. They are caused by the spread of the spirochete via the blood and lymph. Skin symptoms are variable during this stage. They may include the formation of additional papillomas or ulcers and/or the appearance of yellow lesions. A lesion is a damaged area or one with an abnormal structure.

The patient may also experience swelling and pain in the long bones and the joints. Long bones are found in the arms, legs, hands, and feet. Tissue in the bones and joints isn't damaged during the secondary stage of the disease, however. Another symptom that a patient may experience is a condition known as malaise, which is the feeling of being generally unwell.

Tertiary Symptoms

The third stage of the disease develops in up to ten percent of patients. It may begin around five years after the previous stage begins or even later. During this stage the skin, bones, and joints may be seriously damaged. Tissue in the nose, lower jaw, roof of the mouth, and throat may be destroyed.

Transmission and Extent of the Disease

Yaws is transmitted by skin-to-skin contact. People get the disease by touching an exuding papilloma or an open sore on someone's body. The chance of infection is increased if the recipient has a skin wound. The initial infection generally occurs in children and teenagers. People aged two to fifteen are most commonly affected. The effects may last through adulthood if the condition isn't treated in time.

It has recently been discovered that some wild primates (monkeys and apes) carry spirochetes that closely resemble the one that causes yaws. There is no evidence that the disease is passed from these animals to humans at the moment.

Yaws is currently present in at least fifteen countries. Up-to-date records are not available for some places. In addition, it's sometimes hard to distinguish yaws from other diseases and a diagnosis can't be confirmed. Another problem is that advanced tests to identify the presence of the spirochete are unavailable in many communities. The disease is known to be an important public health problem in parts of West Africa, Southeast Asia, and the Pacific, however.

Researchers have noticed that in a few places yaws symptoms are less severe than they once were in that area, and the number of people who develop tertiary symptoms has decreased. The reason for these observations is unknown. Suggestions have included improvement in living standards, the wider availability of health checks, and treatment for other conditions with drugs that also help yaws.

Possible Treatments for Yaws

According to WHO (the World Health Organization), in 1952 a huge effort began to eliminate yaws. Until the 1970s to 1990s, depending on the region, the effort seemed to have worked very well and the number of cases had dropped dramatically. Unfortunately, the incidence of the disease then began increasing again.

In 2012, a Spanish doctor and scientist working in Papua New Guinea made a very important discovery. Dr. Oriol Mitjà found that a single dose of an antibiotic named azithromycin could cure many cases of yaws. His discovery spurred interest in the disease again and renewed the idea that it could be eliminated.

Azithromycin is the preferred treatment for yaws today because it's often effective and well tolerated, it's taken orally, and it's easy for caregivers to administer. It doesn't work for everyone with the disease, though. Fortunately, another treatment is available. A single dose of benzathine penicillin is very often an effective cure for the disease. It has some disadvantages, however. The medication must be given as an intramuscular injection by trained caregivers. In addition, administration by injection is often not well accepted by young patients. In some people, the drug causes an allergic reaction.

Unfortunately, if treatment is started after serious tissue damage has occurred, some of the effects of yaws may be irreversible. The treatment can destroy the bacteria and prevent further damage, however.

Eradicating the Disease

There may be some stumbling blocks to a goal of eradicating yaws in the near future. Positive identification of the disease is important, and its true distribution needs to be discovered. An effective drug must then be administered to everyone who needs it. In addition, the effects of the medication program must be monitored. These processes may take time.

In February, 2018, a significant report from Dr. Mitjà and other researchers appeared in The Lancet. The scientists administered a single dose of azithromycin in the mass treatment of a group of people in Papua New Guinea. Additional targeted treatment was also provided.

At first the treatment protocol appeared to have a high success rate. However, as community members who had been absent during the treatments returned, infections appeared in people who had been treated and the incidence of the disease rose. Visitors from other areas also imported the disease. In addition, the researchers found that a few individuals had genetic resistance to the effect of azithromycin.

The events described above show the importance of monitoring a treated community and of keeping careful records. It also indicates that eliminating the disease may not be easy. More than one mass treatment in an area may be needed, and more than one type of drug may need to be available.

After the effectiveness of azithromycin was discovered, WHO announced a goal of eradicating yaws by 2020. When this article was last updated, the disease still existed. It seems that eradicating it will take more time.

Running from 1952 to 1964, the Global Yaws Control Programme was a big success, treating some 300 million people in 46 endemic countries and reducing prevalence by 95%. But the last mile was never walked. Remaining cases were not adequately traced down, latent infections overlooked, and surveillance measures not enforced, with yaws ultimately resurfacing in many areas.

— Andrea Rinaldi, The Lancet Global Health Blog

A Worthy Goal

Eradicating yaws is important but hasn’t happened yet. The disease is an unpleasant condition and in its worst form can seriously interfere with life. Eliminating it would be wonderful, but the yaws researcher in the second video in this article thinks that reaching this goal is unlikely, at least in the near future. Even if the goal isn't reached soon, I hope the effort to eradicate the disease continues.

The determination of some individuals to treat and monitor the disease is admirable. They need the support of local communities and authorities as well as international ones. The history of yaws treatment has shown that the spirochete will regain the upper hand if it's able to. Diligence is important in order to completely eliminate the disease. Money is needed, too. Azithromycin is being donated by its manufacturer, but many other expenses are involved in mapping and treating the disease.

The eradication of yaws in India has shown us that success is possible. A government-run program eliminated the disease in 2006 and WHO declared the country free of yaws in 2016. Hopefully, the disease will soon be gone from the rest of the world.


  • Flagellar motility of the pathogenic spirochetes from the U.S. National Library of Medicine
  • Information about yaws from the British Medical Bulletin
  • A report about the yaws disease from the World Health Organization
  • Facts about bejel, yaws, and pinta from the Merck Manual
  • Re-emergence of yaws in Papua New Guinea in 2018 from The Lancet
  • Further analysis of the yaws re-emergence in Papua New Guinea from the University of Minnesota

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.

© 2018 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on April 17, 2020:

Hi, Peggy. I hope the disease can be eliminated. I've seen no reports saying that it has disappeared. I hope the 2020 target still exists, but as you suggest, the COVID-19 situation is probably a priority for many researchers at the moment.

Peggy Woods from Houston, Texas on April 17, 2020:

I had never heard of Yaws Disease before reading this. I hope that it can be eliminated. Since 2020 was the goal year to have it accomplished, I wonder if the pandemic of COVID-19 interfered with that goal, or was it already accomplished?

Linda Crampton (author) from British Columbia, Canada on October 24, 2018:

Thank you for the comment, Eman. Chronic diseases can sometimes have a horrible effect on a person's life. It's always good to hear that an effective treatment has been discovered.

Eman Abdallah Kamel from Egypt on October 23, 2018:

It is good to hear about treatment for many chronic diseases and thanks to God for this. This is the first time I hear about Yaws Disease. A useful article and educational as usual.

Linda Crampton (author) from British Columbia, Canada on July 28, 2018:

Thank you very much, Devika.

DDE on July 28, 2018:

Important facts here. Your work is always useful.

Linda Crampton (author) from British Columbia, Canada on July 27, 2018:

Hi, Flourish. In addition to drug treatment of every member of a community, steps to improve general health are being taken in at least some communities. Prevention is important, as you say.

FlourishAnyway from USA on July 27, 2018:

I hadn’t heard of this but am glad that it’s getting support and has been eradicated in some countries. I wonder if they cover prevention strategies too rather than simply seeking to cure it? Seems like that could help, especially since some populations have needed a second round of treatment.

Linda Crampton (author) from British Columbia, Canada on July 27, 2018:

Hi, Jackie. Yes, those of us in certain parts of the world are very lucky. I hope the lady that you describe eventually found help. It's so frustrating when a disorder isn't diagnosed or doesn't get helpful treatment.

Jackie Lynnley from the beautiful south on July 27, 2018:

What a horrible disease, we just don't know how very lucky we are until we see things like this.

I was sitting in a doctors office years ago with a young woman who had something like this in her hands, worse looking really and the doctors would not classify her disabled so she could get some help she said. It was way past arthritis or anything I had ever seen. I don't see how she could even hold a glass or eating utensil. I do hope we soon see some results for all the millions put into research.

Thanks Linda for keeping us so informed.

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Hi, Bede. Yes, penicillin was the preferred treatment before azithromycin started to be used. It is encouraging that people are trying to eradicate the disease, though it seems like quite a difficult task.

Bede from Minnesota on July 23, 2018:

I had never heard of the Yaws Disease, but it’s encouraging to that know groups are working to eradicate it. It’s a remarkable discovery by the Spanish doctor. Did caregivers chiefly administer penicillin to reduce the disease from 1952 onward?

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Thanks for the comment, Manatita. I'm glad the oral antibiotic is so helpful, too. Hopefully it will continue to work well. I hope you have a great week.

manatita44 from london on July 23, 2018:

So it was eradicated in India. I was born in Grenada but I believe that I knew of it then.

So glad that the oral antibiotic helps many. The WHO are always busy with something. God's blessings be with them. Yet another very interesting Hub. Salaam

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Hi, Mary. It's not surprising that you hadn't heard of the disease. It doesn't seem to have been publicized for a long time in this part of the world, but now it's in the news again. I had forgotten about it myself until I read the news and remembered what I heard about it as a child in the UK.

Mary Norton from Ontario, Canada on July 23, 2018:

Linda, this is the first time I have heard of Yaws. I'm glad there is some success in some countries to stop this. I suppose awareness is the start as at my age I should have known of this.

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Hi, Heidi. Yes, that's my fear. It isn't a fatal disease and it affects people in a limited part of the world. These factors may limit people's support. I hope that's not the case for the sake of the people who have the disease or who are at risk of getting it. From a biological point of view, studying the causal organism could be helpful for us.

Heidi Thorne from Chicago Area on July 23, 2018:

Another instance of how a concerned effort can have positive results. I do hope that the progress continues. The concern would be that because it usually isn't a fatal disease, it might get less support.

Thanks for caring and sharing!

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Hi, Bill. Yaws can be nasty. I hope the disease is eradicated soon.

Bill Holland from Olympia, WA on July 23, 2018:

My education continues. I have never heard of Yaws Disease...nasty stuff.

Linda Crampton (author) from British Columbia, Canada on July 23, 2018:

Thank you for the comment, Pamela. I heard about the disease when I was a child, but then it disappeared from the news. It's a shame that it's become a problem again.

Pamela Oglesby from Sunny Florida on July 23, 2018:

I am glad there is hope of irraticating this horrid disease. I had never heard of it before. Great information about Yaws.