Hektoen International

A Journal of Medical Humanities

Dr. Gerhard Hansen – A great discoverer

Howard Fischer
Uppsala, Sweden

Arran Reeve, suffering from leprosy. Copperplate heliogravure by Pierre Arents. Via Wikimedia. 

“No great discovery was ever made without a bold guess.”
– Isaac Newton

Leprosy, from the Greek lepis, meaning scaly, has been known since antiquity. The disease was widespread in continental Europe and in Scandinavia, reaching its peak prevalence in the twelfth century.1 Leprosy was well established in Ireland in the tenth century. It is claimed that Norwegian Vikings had a preference for (kidnapping) Irish women, and brought them, and leprosy, to Norway.2

In the nineteenth century, there were four leprosy hospitals in Norway. The largest and best known was the Lungegård Hospital, in Bergen.3 It was there that Dr. Gerhard Hansen made his revolutionary discovery. Gerhard Hansen, M.D., (1841–1912) was the eighth of fifteen children. His middle-class family had financial difficulties, and he needed to work while a medical student in order to pay his tuition. He did this by tutoring classmates, as well as serving as an anatomy demonstrator. He earned his M.D. with honors from the University of Christiana (now the University of Oslo) in 1866.4 After working as a physician in a fishing village, he went to the Lungegård Hospital and worked under the direction of the leprosy experts Drs. Daniel Cornelius Danielssen (1815–1894) and Carl Wilhelm Boeck (1808–1875).

To further his ability to study leprosy, Hansen learned the latest histologic techniques by studying with experts in Bonn and Vienna.5 The idea in the mid-nineteenth century (and held by Hansen’s chiefs, Danielssen and Boeck) was that leprosy was a hereditary disease. The public considered leprosy a punishment from God.6 Hansen studied tissue samples—affected skin, mucosae, and peripheral nerves—from patients with leprosy. He consistently found, in 1873, rod-like structures resembling bacilli. This finding was ridiculed by the medical establishment, especially when Hansen suggested that these structures may be, in some way, the cause of leprosy. He published these observations in Norwegian in 1874 and in English in 1875.7

In 1879, Hansen generously (and innocently) gave some rod-containing tissues to the German bacteriologist Albert Neisser. Neisser also saw these bacilli and claimed that he (Neisser) had discovered Mycobacterium leprae, the causative organism of leprosy. Hansen was reluctant to start a dispute with Neisser, but his boss, Danielssen (who was also Hansen’s father-in-law), was incensed at this attempted theft of the discoverer’s credit. Hansen was not very active in his own defense because he had not succeeded in growing the bacillus in culture and using it to infect other animals. However, M. leprae is an obligate intracellular organism and simply could not be grown in tissue culture.8

Finally, at a leprosy conference in Berlin in 1897, Hansen was recognized as the discoverer of Mycobacterium leprae. What is even more important is that Hansen was the first to identify a bacterium as the cause of a human disease.9 Hansen’s 1873 paper appeared two years before Robert Koch (1843–1910) demonstrated Bacillus anthracis as the cause of anthrax, or Mycobacterium tuberculosis as the cause of tuberculosis in 1882, and seventeen years before the publication of “Koch’s Postulates,” which clarified the steps needed to prove an organism causes a disease.

Gerhard Hansen was also a recognized zoologist, and a supporter and translator of Darwin. He was an anticlerical atheist who believed that religion preached guilt. His first wife, Danielssen’s daughter, died of tuberculosis during the first year of their marriage. His son with his second wife became a physician and expert in tuberculosis. Gerhard Hansen founded the medical journal Lepra.10,11 It has been written12 that he co-founded the Bergen chapter of the Norwegian Association for Women’s Rights, but this attitude towards “women’s freedom” has been questioned.13

Hansen proposed legislation which became the 1877 and 1885 “Norwegian Leper Laws,” aimed at isolating infected patients.14 It was understood, at the time, that a long period of close contact was needed to spread the infection. Norway had 1,800 people with leprosy in 1875, 575 patients in 1901, and 160 patients in 1920. For comparison, in a given year between 1919–1923, there were 37 people with leprosy in Sweden, 67 in Italy, and 16,261 in Japan.15 The last domestic cases of leprosy in Norway occurred in the 1950s. Since the start of the twenty-first century, one or two people per year have been diagnosed with leprosy in Norway. These patients have immigrated from high-prevalence areas.

Currently there are 0.2 million people worldwide with a leprosy infection, and about 200,000 more are infected each year. The areas of high prevalence are India, Myanmar, Brazil, Tanzania, and Mozambique. Leprosy (Hansen’s disease) can be treated and the infection eliminated with three-drug antibiotic therapy.16 In 2023 the US Centers for Disease Control and Prevention (CDC) reported that “central Florida represents an endemic location for leprosy.”17 The US Food and Drug Administration has approved the use of thalidomide for treating skin lesions caused by leprosy. This anti-inflammatory agent is a teratogen and must not be used if pregnancy is, or will be, a possibility. BCG (anti-tuberculosis) vaccine may provide protection against leprosy.18

In 1970, the Armauer Hansen Research Institute was created in Addis Ababa, Ethiopia. The work of the institute is focused on the immunology of leprosy.19


  1. Göran Wennergren. “Armauer Hansen upptäkt av leprabacillen för 150 år sedan.” Barnläkaren, 3, 2023.
  2. T Vogelsang. “Leprosy in Norway.” Med Hist, 9(1), 1965.
  3. “Gerhard Armauer Hansen.” Wikipedia.
  4. Venita Jay. “The legacy of Armauer Hansen.” Arch Pathol Lab Med, 124(4), 2000.
  5. “Gerhard Henrik Armauer Hansen.” WhoNamedIt? https://www.whonamedit.com/doctor.cfm/596.html.
  6. Wennergren, “Upptäkt.”
  7. Wennergren, “Upptäkt.”
  8. “Gerhard Armauer Hansen,” Wikipedia.
  9. “Gerhard Henrik Armauer Hansen,” WhoNamedIt?
  10. Jay, “Legacy.”
  11. “Gerhard Henrik Armauer Hansen,” WhoNamedIt?
  12. “Gerhard Armauer Hansen,” Wikipedia.
  13. Reshma Kannan. “Gerhard Henrik Armauer Hansen – a legend.” Journal of Skin and Sexually Transmitted Diseases (IADVL, Kerala), 1(2), 2019.
  14. Lorentz Irgens. “The discovery of the leprosy bacillus.” Tidsskr Nor Laegeforen, 122(7), 2002.
  15. I Kobro. “Gerhard Henrik Armauer Hansen (1841-1912).” Annals of Medical History, 1925.
  16. “Leprosy.” Wikipedia.
  17. Aashni Bhukhan et al. “Case report of leprosy in central Florida, USA. 2022.” Emerging Infectious Diseases, 29(8), August 2023.
  18. Mike Seear. Manual of Tropical Pediatrics. Cambridge: Cambridge University Press, 2000.
  19. “Gerhard Henrik Armauer Hansen,” WhoNamedIt?

HOWARD FISCHER, M.D., was a professor of pediatrics at Wayne State University School of Medicine, Detroit, Michigan.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.