Gergard Armauer Hansen
Gerhard Hernrich Armauer Hansen.

The curious doctor who changed the world

2023 will be the 150th anniversary since Gerhard Armauer Hansen discovered the bacteria that causes leprosy. What the young doctor observed through his microscope, was a scientific breakthrough that helped transform how we view disease and infection.

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In the 1800s, leprosy became an increasing problem in Norway. The disease had been known since the Viking Age, but the disease now seemed to be rapidly on the rise, particularly in the small towns along the fjords of Western Norway.

Those affected gradually lost sensitivity and movement in the face and hands, or developed painful, pus-filled and foul-smelling nodular lesions or growths in the skin, especially on the nose and ears, around the eyes and on fingers and toes.

Lepra illustrasjoner
Universitetsbiblioteket i Bergen

Illustrations for Daniel Cornelius Danielssen and Carl Wilhelm Boeck's monograph “Om Spedalskhed” (On Leprosy) published in 1847.

“Little was known about the causes of illness at that time. Physicians had multiple – and competing – theories, while the general population understood the condition to be destiny or a punishment from God. Theologians described leprosy as being present both on Earth and in purgatory at the same time, says science historian Magnus Vollset.

But as the young Bergen doctor Gerhard Armauer Hansen was to find out later that century, the disease was due to neither divine intervention nor human error, but to a small, rod-shaped bacteria named Mycobacterium leprae; better known as the leprosy bacillus.

Kart over lepra i norge, 1800-tallet
Universitetsbiblioteket i Bergen

The map on the left shows the prevalence of leprosy in Norway in 1856. The map on the right shows the same after Bergen doctor Gerhard Armauer Hansen’s discovery.

2023 marks 150 years since the discovery of the leprosy bacillus. This landmark in the history of global health will be celebrated throughout the year, and on February 28 – the date of the first observation of the leprosy bacillus – UiB will hold a commemoration in the University Aula. 

A graveyard for the living

In Bergen, the sick had been gathered at St. Jørgens hospital in Marken since the 1400s. In 1816, the priest Johan Ernst Welhaven wrote a desperate letter to the authorities about the conditions at the hospital, calling it “a graveyard for the living”.

"He also said the condition was a mystery to them. And it is no wonder that it was difficult to understand the disease. Everything from six months and twenty years can elapse between infection and outbreak, and the disease develops in stages that can occur from a few weeks to several years apart. In addition, there are two types – tuberculoid or “smooth” leprosy that affects the nerves, and lepromatous or “nodular” leprosy, that causes the characteristic growths," says Vollset.

Lepra illustrasjon hånd
Universitetsbiblioteket i Bergen

Illustration of a leprosy patient’s arm, from Daniel Cornelius Danielssen and Carl Wilhelm Boeck's monograph “Om Spedalskhed” (On Leprosy) published in 1847.

Welhaven believed that there were great opportunities in Bergen for researchers who wished to solve the leprosy riddle. It took time, but by the end of the 1840s the authorities established a separate research hospital with a doctor, and founded the care foundation Pleiestiftelsen in Kalfarveien which could accommodate 280 patients. There was great optimism that within a few years a cure would be found, and the disease would soon be eradicated.

"But it turned out to be more challenging than they had imagined. In what became the reference work for the next 50 years, the doctor at the hospital, Daniel Cornelius Danielssen, and his colleague Wilhelm Boeck from the University of Kristiania described the condition as a ‘hereditary dyscrasia’, or imbalance in the blood. They based this assumption on the fact that the majority of those infected were related to each other. The use of the Latin expression was probably a way of concealing the fact that they simply did not know what mechanisms were involved,” says Vollset.

Kalfaret i Bergen, 1865/1866
Knud Knudsen, Universitetsbiblioteket i Bergen

Photo taken from Kalfarveien facing Kalfaret in 1865/66. The two buildings to the right in the photo are the care foundation and the research hospital. The sick lived here for the remainder of their days and had little power to decide over their own lives and daily activities.

Locking up the sick

The years went by without the doctors at the hospital getting any closer to a cure. At the same time, young Gerhard Armauer Hansen was growing up in the narrow streets behind St. Mary's Church in Bergen, and then left for the capital Kristiania to become a doctor.

At St. Jørgen’s Hospital in Bergen, new remedies were constantly tested – but neither baths, ointments, drugs nor hot and cold treatments had any effect.

At the same time, the national patient registry, established in 1856, showed something remarkable. The registry was established to investigate whether it would be possible to predict who would develop the disease, and now it revealed that the number of new cases was rapidly declining.

Gerhard Armauer Hansen
Universitetsbiblioteket i Bergen

The young doctor Gerhard Armauer Hansen returned to his hometown after graduating from medical school, and found employment at the leprosy hospital.

When the newly graduated Armauer Hansen returned to Bergen in 1869 and got a job at the leprosy hospital, he immersed himself in these statistics. He discovered that the decline was happening far too quickly for the disease to be hereditary. In that case it would have taken a generation for the number of infected people to start to decline.

"The decline happened much faster than that. He gets the idea that the disease can be transmitted through contact between people, and develops a theoretical model to find how quickly it would then spread. As he applies the model in comparing rural districts who have sent infected people to an institution against those who have not, he sees that his theory is correct”, says Vollset.

The number of new cases is greater where the sick live among the healthy. This indicates that there must be an infectious agent at play.

The breakthrough

Armauer Hansen raised funds to buy a microscope and began the search for the infectious agent. He collected samples from the lesions of both living and dead patients and examined them under the microscope.

And then, on the evening of February 28th, 1873, he finally made a discovery. Through the microscope, he clearly saw small, rod-like bodies that moved as he poked at them. "Is this a bacillus?", he writes in his lab journal that evening.

"This is pure curiosity-driven basic research, and represents the beginning of one of the few real paradigm shifts in the history of medicine. That night, Armauer Hansen became part of the trio behind the bacteriological revolution in medicine, along with Louis Pasteur who discovered pasteurization and Robert Koch who found the bacterium that causes tuberculosis. They changed the way we look at disease and infection today," explains Vollset.

Magnus Vollset
Torill Sommerfelt Ervik, UiB

Science historian Magnus Vollset in Armauer Hansen's laboratory in Kalfarveien.

The first to mention Armauer Hansen's discovery was the British doctor Henry Vandyke Carter. He was on a research stay in Bergen at the time, and at the end of 1873 he published a report on his observations. Hidden in a footnote in the report from Bergen, he mentions a young doctor who has observed rod-like bodies in tissue samples from the sick. "If this is true, it could change everything," he notes. And he's right about that.

Met with international resistance

It doesn't happen overnight, yet slowly but surely people start to realize the impact of Armauer Hansen's discovery. The most concrete changes in Norway can be found in the legislation. Several laws were put in place in the following decades to limit the rights of infected people.

The leprosy patients were now to be quarantined, either at home with a separate bedroom and their own cutlery, or in institutions where all their movements were closely monitored.

"The legislation affected different groups very differently. While the more affluent could stay at home, the poor were de facto sentenced to a life in imprisonment, for the sake of the healthy majority," says Vollset.

Hagen til Pleiestiftelsen for spedalske
Universitetsbiblioteket i Bergen

Photo of patients in the garden of the leprosy treatment centre, Pleiestiftelsen for spedalske. The patients’ lives were strictly regulated, down to how many grams of bread and milk they received per day and when they should wake up and go to bed.

But there were also those who doubted the young scientist. Internationally, there was opposition to the theory that something as small as bacteria could cause disease and spread between people.

"This frustrated Armauer Hansen, and he was determined to convince the critics. He was confident that he could save millions if he could just prove that leprosy was contagious," Vollset said.

First, he tried to demonstrate infection in animals, such as rabbits and pigeons, but without success. In correspondence with his colleague Robert Koch, he describes his attempts with exasperation. "Have you ever seen a leprous rabbit?" Koch responds. Armauer Hansen realises that if he is to prove the infectiousness of the disease, then he must demonstrate human transmission.

The human experiment

One autumn day in 1879, Armauer Hansen summoned the leprosy patient Kari Nielsdatter Spidsøen into his office at St. Jørgen’s Hospital. He told his assistant to restrain her, and then proceeded to make a small incision in the thin skin under her eye, before rubbing something into the wound and dismissing her.

"Nielsdatter Spidsøen had the “smooth” form of leprosy, and was already admitted as a patient at the hospital. Thus, Armauer Hansen knew that she was susceptible to infection, and he had the opportunity to monitor her. He wanted to see if he could give her the nodular form of leprosy. The patient was never informed of the purpose of the procedure," explains Vollset.

Nevertheless, Kari Nielsdatter Spidsøen realised what she has been subjeced to. She visited the priest several times with her concerns that they wereconducting human trials at the hospital. The priest believed her, and the case ended up in court.

Gerhard Armauer Hansen
Universitetsbiblioteket i Bergen

Gerhard Armauer Hansen was determined to prove his infection theory. The photo was taken sometime between 1890 and 1910.

"And although Armauer Hansen was part of the elite, while she was from the lowest social class, the court believed her explanation and ruled that Armauer Hansen no longer had the right to practice as a doctor. No one was above the law. It was a very progressive ruling at the time and set a precedent for informed consent in medical trials," says Vollset.

Still, Armauer Hansen received support in the medical community, which largely defended his actions. The research question was important, and his method was considered to be the best way to test the infection theory. His career was largely unaffected by the verdict. He moved his office from the hospital to Bergen Museum and continued his research, enjoying great respect for the rest of his life.


Today, a vaccine against leprosy is being tested, and since 1980 the WHO has been distributing medicine – free of charge – that kills the bacteria in infected people. We also know today that the disease is not very contagious. 95 percent of people are genetically immune, and the remaining 5 percent must, in addition to being exposed to the bacterium, have had a weakened immune system over time to develop the disease.

"Leprosy is the least contagious of the world’s contagious diseases. But in many countries there is still a strong stigma associated with the disease, and prejudices and misunderstandings flourish. In addition, many have to live with injuries from the disease due to prejudices that keep them from seeking help until it's too late. And in that period, they may have exposed others to infection," says Vollset.

Over the past two decades, with the exception of the years of the Covid-19 pandemic, 200 000 new cases were reported globally yearly. Most infected people live in Southeast Asia and India, but Africa and Latin America also have a large number of cases.

"Now that we are commemorating the 150th anniversary of Armauer Hansens discovery of the leprosy bacillus, we also recognise that there are two sides to the discovery. On the one hand, it was a world-class breakthrough that provided a rational explanation for what was once thought to be uncleanliness or a punishment from God. Yet on the other hand, it led to a widespread fear of infection that has caused people to shun those afflicted. In Norway, this is a thing of the past – but that’s not the case in the rest of the world. We dream of eradicating leprosy for good, but for that to be possible, we must first eradicate the stigma," says Vollset.