150 years ago, the Norwegian physician Gerhard Armauer Hansen made a discovery that would change the world. In tissue samples from leprosy patients in Bergen, Norway, he identified small rod-shaped organisms: M. Leprae, the pathogen that causes the disease. This was, and remains, “one of the most important discoveries in global health”, as Director-General of the World Health Organization (WHO), Dr. Tedros Ghebreyesus, recently put it.[1] Why? How can an observation made in 1873 still be relevant to the fight against humanity’s most misunderstood disease?

The Past: Interpreting a Discovery

One lesson from history is coming to terms with the same event having widely different meanings. For Hansen’s discovery, there are at least three competing interpretations that are all true.

The first, is one of scientific achievement. In textbooks, Hansen is sometimes presented in the same breath as Louis Pasteur and Robert Koch, the fathers of bacteriology and microbiology. Hansen communicated with both, and his discovery of the leprosy bacillus happened seven years before Koch’s discovery of the bacillus causing tuberculosis. Hansen helped give birth to the way we understand infectious disease today.

The second, is one of disenchanting misconceptions. The disease, which untreated causes severe disabilities, has been known and feared since time immemorial. Hansen’s discovery showed that rather than a divine curse, the disease had a rational and material cause. He showed that leprosy was a disease like any other and opened the door to the development of effective treatments.

The third, is one of justifying segregation and human experimentation. To Hansen, the pathogen proved the disease spread from the sick to the healthy. With no treatment available (then), the solution was identifying those affected, followed by life-long isolation. Hansen advocated segregation for the sake of the healthy majority at a global scale. He also lost his right to practice medicine after conducting an experiment on one of his patients. While the disease in some parts of the world is referred to as “Hansen’s disease” to distance it from the disease described in the Bible, others claim this is an honor Hansen does not deserve.[2]

The Present: Neglected and Stigmatized

Since the early 1980s, effective medications have been distributed by the WHO to every person in the world diagnosed with the disease. In the 1990s, the goal of reducing the prevalence of disease to less than 1 per 10.000 population at country level led to a global campaign that inspired the Millennium Development Goals and succeeded in reducing the prevalence of the disease by more than 95 percent. By the end of 2000, leprosy had been eliminated as a public health problem on a global level and by a majority of the countries. Since then, however, progress has stagnated. Around the world, about 200.000 new cases are still detected every year, and many are probably left undiagnosed. Between three and four million people live with disabilities caused by the disease.

A major obstacle is stigma and discrimination, which leads to people hiding their disease and not receiving treatment. Those affected are usually among the poorest, living in places with underdeveloped health systems, and face stigma and discrimination even if cured. The past decades, the United Nations have passed several resolutions advocating the abandonment of outdated and discriminatory laws and have appointed a special rapporteur on discrimination against persons affected by the disease and their family members.

The Future: “Last Mile”-Challenges

Leprosy has been the target of longer and more concerted efforts than any other disease in human history. Moving into the future there are lessons to be learned, both from achievements and abuses conducted in the name of the greater good. June 21-22 this year, leprosy stakeholders from around the world will meet in Hansen’s birthplace of Bergen, in Norway, to gather momentum for a world with zero leprosy. As we, the organizers, see it, three major “last mile”-challenges remain.

The first, is medical. While the current treatments are effective, more tools are probably needed. Post exposure prophylaxis with single dose rifampicin is associated with a 57% reduction in risk of leprosy among contacts after 2 years and is promoted as part of the Global Leprosy Strategy 2021-2030.[3] A vaccine candidate, LepVax, is in stage 2 of development. However, the dramatic reduction in number of cases has been accompanied by a loss of frontline expertise in early diagnosis. How do we improve our medical expertise and ensure it reaches those who need it the most?

The second, is social. As mentioned above, stigma and discrimination remain major obstacles to achieving zero leprosy. Part of the problem is lack of knowledge that leprosy is a treatable chronic disease with very limited contagiousness. Another part of the problem is attention to the recently adapted WHO strategy towards zero leprosy by 2030.[4] How do we fight stigma and discrimination and ensure the disease is not forgotten?

A third, is historical. Solving a public health issue means the problem stops existing, and that lessons learned on the way stop being seen as relevant. How do we preserve and communicate the history of the disease, and ensure lessons are learned and applied to this and other threats to public health?

The discovery of M. Leprae happened 150 years ago, and it is still changing the world. Now, we have a window of opportunity to finally reaching zero leprosy. It is our sincere hope this is the last anniversary before leprosy is found only in museums and history books. The event is free of charge, thanks to generous funding from Sasakawa Leprosy (Hansen’s Disease) Initiative and will also be streamed for free online.[5]

MAGNUS VOLLSET, PhD
Head of the Hansen 2023 anniversary committee at the University of Bergen
TAKAHIRO NANRI, PhD
Executive Director of Sasakawa Health Foundation and Sasakawa Leprosy Initiative

[1] WHO Director-General Tedros Ghebreyesus’ speech at the anniversary event February 28, 2023, is available here: https://hansen2023.org

[2] See for instance: Deps P, Cruz A. Why we should stop using the word leprosy, Lancet Infect Dis 2020; 20: E75-E78; Butlin CR, Lockwood DNJ. Why we should stop using the word leprosy, Lancet Infect Dis 2020; 20: 900–01; Deps P, Cruz A. Why we should stop using the word leprosy. Lancet Infect Dis 2020; 20; 1236.

[3] World Health Organization. (2018). Guidelines for the Diagnosis, Treatment and Prevention of Leprosy, xiii; World Health Organization. (‎2021)‎. Towards zero leprosy: global leprosy (‎Hansen’s disease)‎ strategy 2021–2030. World Health Organization.

[4] WHO 2021.

[5] Learn more: https://hansen2023.org