Yaws is a tropical infection, which is sometimes confused with the sexually transmitted infection syphilis.
There are two reasons for this.
- Yaws is caused by a bacterium (Treponema pallidum pertenue), which is closely related to the one that causes syphilis (Treponema pallidum pallidum).
- The standard blood test for syphilis is also positive in people who have had yaws.
Yaws could in theory be passed on during sexual relationships, but in practice it's nearly always transmitted by simple contact between people's skin.
For instance, a child may catch it from playmates or from parents. The bacterium gets in through a crack or cut in the skin – often on the legs.
So it is definitely not a sexually transmitted disease (STD).
Yaws used to affect hundreds of millions of people across the hot, humid regions of the world. But at the last count, there were less than two million sufferers worldwide.
In 2012, the World Health Organisation announced a new campaign to try and eradicate this infection from the globe by 2020.
In 2014, indications are that they may succeed. For instance, in India (once a hotbed of the disease), there have been no cases for three years.
In Britain, yaws is now almost unknown. But instances have occurred where people who have spent their childhoods in the tropics, especially in Jamaica, have been mistakenly diagnosed in the UK as having syphilis, because their blood tests were positive.
The person develops a skin lump, often on the legs. A crust usually forms, and then comes off, leaving a bright red, raspberry-like appearance. Similar skin lesions then appear nearby.
If the disease isn't promptly treated, the patient may go on to develop painful deformities of the bones and joints, as well as damage to the nose.
Treatment with penicillin (or azithromycin) cures this disease completely.
However, the blood test may remain positive for many years, even though the person's health is good.
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