With a new rapid-result blood test and a vaccine in the works, leprosy eradication may soon be a reality, says immunologist Malcolm Duthie, who created the test
Most people think of leprosy as a problem of the past. How common is it today?
There are about 250,000 new cases reported each year. But that's probably about 5 to 6-fold lower than actually occur. In one study in Bangladesh, for example, they detected a rate sixfold higher than what was reported.
Why is leprosy so under-reported?
It is very easily misdiagnosed. In the mid-1980s there were about 12 million cases globally. Then the World Health Organization led a drive to reduce cases to less than 1 per 10,000 people by 2000. Since then levels have plateaued. But an unfortunate consequence of that success is there are now fewer clinicians who can diagnose leprosy – and the front line is clinical recognition.
How is a leprosy infection confirmed?
You need to collect lymph fluid, or take a biopsy and look for evidence of Mycobacterium leprae. But none of this is rapid, and it requires significant expertise. People are commonly treated for fungal infections or other skin conditions. It is often a last resort, after multiple wrong diagnoses, that they end up at leprosy reference centres. That delay is critical; the longer the infection goes on, the greater the chance that person is going to have lasting nerve damage.
Your team has developed a new blood test for leprosy. How early can it detect infection?
In a lab-based study, we were able to identify most cases about 9 to 12 months in advance of clinical symptoms. That is probably conservative.
How easy is it to use the test?
It is like a home pregnancy test, but with blood. You take a finger prick, collect a drop of blood, add it to a window in the test, and it causes a colour change. It doesn't have to be done by a specialist.
The test was developed as an offshoot of your leprosy vaccine programme. How close are you to a vaccine?
Our timeline, if everything goes to plan, is to have a phase 1 clinical trial at the end of this year or the start of next year. Actual implementation of the vaccine is probably several years down the track.
Do you think we can eradicate leprosy?
Yes, there is the potential. About 65 per cent of cases are reported in India. The one significant hurdle is that, with a population of 1.2 billion and a disease that officially affects about 150,000, there's probably not going to be widespread implementation of the vaccine. That is why we want our blood test, so we can target regions to implement the vaccine. The WHO mantra is early detection, early treatment. Well, early detection based on clinical symptoms is often too late.
So would the strategy be like that used to eradicate smallpox – by targeting hotspots?
Exactly. An infection with a clinical onset of seven years is not going to advance as rapidly as smallpox, but that's the model. Identify the hotspot, treat the hotspot, knock the disease down in a particular region and then keep an eye on that region.