A rapid diagnostic test to identify yaws, a debilitating skin disease which affects thousands of the world’s poorest children, could reinvigorate efforts to eradicate the illness, experts say.
The molecular test, which detects yaws within 30 minutes, could allow on-the-spot diagnosis in remote regions – eliminating the need to transfer disease samples for hours or even days to high-tech laboratories for expensive tests.
Yaws is a bacterial disease (caused by the bacterium
Treponema pertenue) which spreads through skin-to-skin contact and causes skin lesions and ulcers all over the body. Though easily treated with a single dose of antibiotics, yaws still impacts more than 46,000 people globally—75 to 80 percent of whom are children under the age of 15 years old.
It is not fatal but if left untreated, the illness leads to chronic disfigurement and disability.
“Yaws affects children living in very rural, hard to reach communities – there is a saying that where the road ends, that is where yaws begins,” said Laud Anthony Basing, biomedical engineering research graduate at Purdue University in the US, and creator of the rapid test.
“It eats into the skin, into the bones, into the cartilage, and if you do not treat it the child will grow up with deformities or disabilities,” he added.
More than 80,000 suspected cases of yaws were reported to the World Health Organization in 2018, but the real number of infections is likely to be much higher.
Just 15 countries known to be endemic with the disease record cases, but more than 70 other nations which previously saw high rates of yaws no longer track infections.
While most people today have never heard of yaws, it was once the subject of an ambitious eradication campaign.
Between 1952 and 1964, Unicef and the WHO screened some 300 million people for the illness, in a coordinated programme which treated more than 50 million cases. Yaws was on the brink of being wiped out and reports of the disease dropped by 95 per cent.
But eradication efforts were a victim of their own success. Yaws-specific programmes were dismantled and existing health care systems were left to tackle the ‘final cases’. Resources and attention disappeared as other illnesses took priority – yaws and attempts to eradicate it were largely forgotten.
That was until 2012, when a team led by Oriol Mitjà in Papua New Guinea found that a single dose of the antibiotic azithromycin cures yaws within four weeks. The drug is safer and easier to administer than previous treatment – a penicillin injection in the buttocks.
The discovery led the WHO to renew its strategy to wipe out yaws, setting an audacious goal to eradicate the illness by 2020 – though this target is likely to be pushed back to 2030.
“The question is, did these countries [which no longer report cases] get rid of yaws in the 1950s and 1960s, or do they still have cases in isolated, poor populations where we are not looking?” said Dr Michael Marks, assistant professor and yaws expert at the London School of Hygiene and Tropical Medicine.
“Because there's currently no good estimates in much of the world, it's plausible that numbers [of cases] will actually go up as surveillance improves, before they go down,” he added.
But as the world moves closer to reaching eradication accurate and portable diagnostics are needed to confirm cases.
Currently DNA samples are either taken to laboratories and tested using a complicated technique called polymerase chain reaction (PCR), or rapid syphilis tests are used – the disease has an almost identical genetic makeup to yaws.
But to certify the illness as eliminated and paint a better picture of the global prevalence, a portable but accurate DNA test is required.
“This work is extremely important,” said Dr Kingsley Asiedu, from the WHO’s department of control of neglected tropical diseases. “We will need a molecular test that is deployable in the field soon so we can move from reference labs in cities to tests that can be used to absolutely confirm cases in remote areas.”
“We don’t want to wait until the final cases – the yaws endgame – to have these tests in use,” he added. “I would like to see Anthony’s molecular test developed and used as soon as possible.”
The new rapid yaws-specific diagnostic, which tests a swab of saliva, costs $2 per use and has yielded “impressive results” in small trials, said Dr Basing.
He was one of 30 finalists of the WHO Innovation Challenge – which saw more than 2,400 entries – and showcased the rapid test at the Africa Health Forum in Cape Verde earlier this year.
“Going forward we would like to do larger scale testing with a lot more samples,” Dr Basing said.
“But I think that by the year 2020, we can actually start the yaws eradication process with mass drug administration and with diagnosis and treatment at the same time. If we do this, within a few years we can eradicate yaws,” Dr Basing added.
But not everyone is certain the test is the answer.
“We will probably continue to use PCR in labs as we get to the final cases,” said Dr Marks. “I think this [test] is a valuable contribution and will be useful in many settings, but currently is probably not going to replace PCR.”
