Eliminating a disease is not something that happens thanks to one organisation or one group of people in isolation; eliminating a disease requires partnerships across the world from all levels of society. But, leading the charge towards a world where leprosy has been eliminated are the scientists that are cracking the codes of leprosy transmission.
The researchers at the Stanley Browne Research Laboratory in India are working on three key research projects that are driving us towards zero transmission. One focuses on epidemiology, another is concerned with a PCR test for leprosy, and the last is about mud.
Our scientists in India have been tracking the spread of leprosy within an eight block radius of high leprosy transmission in Purulia, India. They have taken samples from 112 people who have been diagnosed with leprosy and their close contacts. The team have extracted the leprosy DNA from these samples so they can be tested for genotypes.
Genotyping is the process of determining differences in the genetic make-up of an organism. It is how we can see the genes that have been passed on from your parents to you. In the case of leprosy, it allows us to see which strain of leprosy a person has and where that has come from.
How does that help us end leprosy transmission? Imagine a mother and daughter living in a home in Purulia. The team have taken a swab from both the mother and the daughter. The mother’s swab contains leprosy DNA, as does the daughter’s swab. However, the genotyping reveals that the leprosy DNA in the two swabs is different – it has different genes, so it must be a different strain. This tells us that the daughter did not contract leprosy through her mother; she must have contracted leprosy elsewhere.
This knowledge could then direct our field teams to determine the real source of the transmission. Perhaps there is a classmate at the daughter’s school who has undiagnosed leprosy. Perhaps it is one of the children from a neighbouring home that the daughter plays with regularly.
Genotyping will allow our teams to narrow down the source of transmission. Their contact tracing does not stop simply with the mother, but extends until the index case is identified. Through this, we are in a better position to look for signs and symptoms, to provide treatment, and to provide post-exposure prophylaxis (PEP) in the form of one or more antibiotics.
As leprosy programmes across the world look to expand their PEP, contact tracing, and active case finding efforts in line with the new WHO leprosy strategy, this technology will allow them to be more targeted than they ever could have been before.
This is true on a local scale, like within a household or neighbourhood, and also on a much larger scale. Certain strains of leprosy are more common in particular parts of India and our scientists are now better equipped to identify how these strains are spreading, where they are starting, and if there are interventions we could be making to interrupt this transmission.
At some point in the last two years, all of us will have taken a PCR test for Covid-19. A PCR test allows researchers to make copies of a small section of DNA or RNA, which means they can produce the large amounts of DNA they need to perform molecular and genetic testing.
Over a number of years, our team in India have been testing one gene marker of leprosy at a time to determine which of these genes have the most sensitivity to tests. In October 2021, the Stanley Browne Research Laboratories were in a position to combine three of the most sensitive gene markers into one multiplex PCR test.
This test is 90 percent successful at diagnosing cases of leprosy, including the really early cases of PB leprosy. Previous tests have only been 60 percent effective and this test is nearly at a stage which could see it rolled out as a field-friendly, small, battery-operated testing machine that works through nasal swabs.
This multiplex PCR test is being perfected and prepared for an initial pilot within India’s leprosy programmes. By 2024, it could be ready for a global rollout that would make leprosy diagnosis faster and more effective than ever before. It could be a game changer in our fight to end leprosy transmission by 2035.
The Stanley Browne Research Laboratories are world leaders in the understanding of environmental reservoirs of leprosy bacteria.
The leprosy bacteria, M. leprae, is most commonly understood to be transmitted from human to human. However, leprosy has also been identified in armadillos - who are known to transmit leprosy to humans. The UK’s Red Squirrel population, and a wild chimpanzee population in West Africa have also been identified as carriers of leprosy bacteria, although there is no evidence of transmission between these animals and humans.
Our researchers in India have been looking at the extent to which leprosy bacteria can also be found within soil and water.
They have been looking at remote villages in India where there is a high level of leprosy transmission and only one water source per community. They have tested both the water and the soil surrounding this water source to identify leprosy DNA and, where viable leprosy bacteria is found, they have used genotyping to compare this to leprosy DNA from the recently identified leprosy cases in the village. Through this, they can draw a direct link between new cases of leprosy and leprosy DNA that is found in water and soil.
So far they have identified a link between leprosy DNA that they found in soil and water and new cases of leprosy that have been identified in 20 separate families.
This research has been conducted within Purulia and Chhattisgarh, where communities are underdeveloped and suffer from poor WASH facilities.
If we can identify that viable leprosy bacteria from water sources in these villages is leading to members of the local population developing leprosy, we can take this knowledge to local governments. We can make the case for new wells in these communities so that people can access clean water, which will not bring the risk of leprosy transmission.
The knowledge from this project could be used across the world, it can focus our WASH efforts, and it can be another tool in our advocacy toolbox.
Photo credits: Ruth Towell
