The disease now known as Hansen's disease was for centuries called leprosy. It was once among the most feared of all medical disorders. Patients were commonly isolated from the general community in leper colonies, such as the one founded in the Hawaiian Islands by Father Damien. In fact, the term leper longago became synonymous with the person who was outcast by society.

Until the mid-nineteenth century, Hansen's disease was thought to be a hereditary condition or a disease of the blood. Researchers had unsuccessfully attempted to induce the disease in animals by injecting them with cells from Hansen's patients. Some scientists had even tried to infect themselves in this way, without success. As a result, most authorities were convinced that the disease was not infectious.

The correct explanation for the disease was provided in about 1869 by the Norwegian physician, Gerhard Henrik Armauer Hansen. Hansen was born in Bergen, Norway, on July 29, 1841. He received his medical degree from the University of Christiana (now Oslo) and two years later joined the medical staff at the Lungegard Hospital for Leprosy in Bergen. He spent most of his life working onthe cause and treatment of the disease that ultimately received his name.

In the early 1870s, Hansen began to report his observations on the epidemiology and etiology of leprosy. He was fortunate to discover a number of communities in which the disease was very common, occurring as frequently as one in athousand. Through extensive interviewing, he was able to demonstrate that the disease was almost certainly not transmitted genetically. He wrote that although he had "not been able to furnish any decisive proof in any direction,"he was convinced that leprosy fell in the "category of specific diseases which are contagious."

An important element in this conclusion was the discovery of "small staff-like bodies, much resembling bacteria, lying within the cells [of leprosy patients]." He suspected that the "large brown elements" he found in patients' cells were involved in the transmission of the disease. In 1880, Hansen named these infectious particles Bacillus leprae.

The identity of the "large brown elements" was finally determined when the German physician, Albert Neisser (1855-1916), visited Hansen in 1879. As a result of Neisser's work, the infectious agent was identified as the organism, Mycobacterium leprae.

Hansen's career at the Lungegard Hospital came to an end in 1880 when he inoculated one of his patients with live leprosy bacilli without obtaining her permission. Despite this setback, he continued working to improve the conditions of leprosy patients until his death in Fluro, Norway, on February 12, 1912.In 1997, there were an estimated 1.2 million cases of leprosy worldwide, with an estimated half a million new cases occurring each year.

As of 1998, India, Indonesia, and Myanmar account for 70% of all leprosy cases. The World Health Organization has recommended combinations of rifampicin,clofazimine, and dapsone for the treatment of leprosy. Thalidomide has also been approved by the U.S. Food and Drug Administration for use against ENL (type II lepra reaction), a severe complication of leprosy.

An important breakthrough in leprosy research occurred in 1985. A research team at Stanford University cloned five genes from M. leprae. This accomplishment is of considerable significance since it provides a basis on whichan anti-leprosy vaccine can be developed. In fact, the development of such avaccine is now well under way, providing hope that this disease may some daybe controlled.

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