International Leprosy Association -
History of Leprosy

International Leprosy Association -
History of Leprosy


Dr Gerhard Armauer Hansen

Status Physician, Medical Researcher
Country Norway


Gerhard Armauer Hansen (29 July 1841 – 12 February 1912) was a Norwegian physician known for his discovery of Mycobacterium leprae, the bacterium that causes leprosy (sometimes called Hansen’s bacillus).

Hansen was born in Bergen, Norway, and studied medicine at the University of Christiana (now University of Oslo), graduating with honours in 1866. He completed his internship at the National Hospital in Christiania (Rikshospitalet), and afterwards briefly served as a doctor to the fishermen who worked in the Lofoten archipelago.

In 1868 Hansen returned to his native town of Bergen, which was centre of European leprosy research. At this time, Norway had around 3000 leprosy patients, more than any other European country, and the disease was most concentrated in Bergen, which had three leprosy hospitals. Hansen initially worked in Pleiestiftelsen for spedalske nr 1, but soon moved on to the position of assistant physician at the Lungegaardshospitalet, where he worked under Dr Daniel Cornelius Danielssen, a foremost authority on the clinical and pathological aspects of the disease. With C W Boeck, Danielssen in 1847 had published the major work Om Spedalskhed (On Leprosy); he had also helped to organise Bergen's leprosy care program.

While Danielssen regarded leprosy as hereditary, Hansen was convinced that a bacterium carried the disease from person to person; a daring speculation at a time when the concept of contagion was still poorly understood, and no one had shown that bacteria could cause human diseases.

In his first work of 1869, published in Norwegian only in 1871, Hansen among other things described the appearance of leprous changes in lymphoid tissue. Here Hansen applies the term ‘infectionsstoff” (‘infectious substance’) for the changes he saw in association with lymph nodes. He was, however, uncertain about what these findings really meant. His poor equipment complicated his work, and he was unsuccessful in his attempts to cultivate and stain the changes.

In 1870 a grant allowed Hansen to travel to Bonn and later to Vienna for advanced training in histopathology. Returning to Norway, using primitive staining methods and working with biopsy specimens from patients with leprosy, Hansen continued his intensive microscopy work.

On his return to Bergen in 1871, Hansen launched his search for the causative agent of leprosy, using biopsy specimens drawn from patients. Hansen decided to look for bacteria in patients, first in blood and, on finding none, in skin nodules. He wrote: ‘At that time ... I could sit tirelessly for hours on end, focusing through the microscope with great enlargement ... One day I was positive I had discovered the bacteria, the next day magnificent certainty had collapsed, and I would be back where I started ... Finally, though, I wrote the first record of my research.’

In 1873, aged 32 years, Hansen re-examined leprous skin nodules and discovered the rod-like bodies inside cells that looked like bacteria; they were not present in all cells, but in most of them. He believed these bodies to be the causative agent of leprosy and thereby became the first to suggest that microorganisms might cause a human disease. He published his findings in an 88-page monograph in 1874, but remained cautious: he wrote, ‘Though unable to discover any difference between these bodies and true bacteria, I will not venture to declare them to be identical.’ Hansen’s hesitance to claim that the rod-shaped bodies were actually bacteria would later cause problems: in 1879, Albert Neisser attempted to claim discovery of the leprosy bacillus, using material he obtained from Hansen during a visit to Bergen. Hansen was outraged, and updated his original report to publish new articles simultaneously in English, German, and Norwegian journals in 1880, establishing his priority in the discovery.

In recognition of his discovery, Hansen was appointed Chief Medical Officer for Leprosy in Norway in 1875. He believed that the isolation of leprosy patients was crucial to stop the spread of the disease, and he developed a series of laws to put such a system into effect in Norway. An 1877 law required impoverished people with leprosy to be isolated in special homes instead of travelling from place to place in search of aid. A second law, passed in 1885, was much more widespread, requiring all people with leprosy to be isolated from their communities and families (except for spouses). Many in the medical community were not firmly convinced that leprosy was contagious, and protested the laws as inhumane. However, opposition decreased as leprosy began to decline in Norway. Many other countries soon adopted similar laws.

Because the hypothesis that leprosy was contagious, as opposed to hereditary, was still unproven, Hansen conducted a study among emigrants to the United States who had leprosy. He observed that none of the subjects’ descendants developed leprosy; in combination with his discovery of the leprosy bacillus, this allowed him to establish that leprosy is a contagious disease. He presented these findings at the first International Leprosy Conference in Berlin in 1897.

Hansen's discovery of Mycobacterium leprae was historic for reasons beyond its significance to the fight against leprosy. As the first identification of a bacteria as the causative agent of a human disease, his study was a precursor to Robert Koch's conclusive demonstration of the bacterial cause of anthrax in 1875, and the tuberculosis bacillus in 1882.

Although Hansen was never able to cultivate the leprosy bacillus in vitro as an experimental confirmation of his hypothesis, it has still not been done. His research helped to establish fundamental principles in immunology, bacteriological medicine and public health policy.

Hansen married Stephanie Marie, the daughter of his mentor, Daniel Danielssen, in 1873, but she died of tuberculosis the same year. He remarried in 1875. Hansen died of a heart attack in 1912. In his honour, leprosy is sometimes referred to as Hansen’s disease.


Grzybowski, Andrzej, Guido Kluxen, and Klaudia Półtorak. "Gerhard Henrik Armauer Hansen (1841–1912) – 100 years Anniversary Tribute." Acta Ophthalmologica 92.3 (2014): 296-300. Web.

Jay, Venita. "The Legacy of Armauer Hansen." Archives of pathology & laboratory medicine 124.4 (2000): 496-7. Web.

Marmor, Michael F. "The Ophthalmic Trials of G. H. A. Hansen." Survey of Ophthalmology 47.3 (2002): 275-87. Web.

Schmidt, Mathias. "The 100th Anniversary of Armauer Hansen's (1841-1912) Death." Leprosy review 83.4 (2012): 408. Web.


On the Etiology of Leprosy, British and Foreign Medico-Chirurgical Review, 55 (1875): 459-89.
- (Letter) "On the Prevention of Emigration and Immigration of Lepers", Lepra, 1 (1900): 88-9.
- Hansen, G Armauer and Carl Looft. Leprosy: in its Clinical and Pathological Aspects, trans. Norman Walker. Bristol: John Wright, 1895.

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