The global spread of leprosy is directly related to human migration patterns throughout history. Although the origins of leprosy are not certain, the disease most likely originated in East Africa or India. This theory of origin is linked to the four genetic types of leprosy. There are also historical implications as well, "Confirmed reports of leprosy first appear around 600 B.C.E. in sacred Indian texts that describe a victim's loss of finger and toe sensation--a hallmark of the damage the bacterium Mycobacterium leprae inflicts on the nervous system" (Grimm 2005). Leprosy would then spread east into the rest of Asia and into the pacific islands. Trade facilitated the spread of the disease and was identified in China around 400 B.C. It continued to travel from China into Japan and later into Oceania by the eighth century A.D. (Barnes 2005:181). Historical documents as well as archaeological data help reinforce this theory of migration into Asia. "In the Southeast Asia and India where the modern dominant SNP group is type 1, archaeological skeletal remains with lesions of lepromatous leprosy have been excavated and dated from ca. 2000 BC (India) to ca. 300 BC-500 AD (Thailand); therefore the type 1 genotype in modern Japan might be traced back to Southeast Asia and probably originated in India" (Suzuki et al. 2010).
Migration West into Europe and the Americas
Leprosy spread into Europe later then Asia with the first written accounts of leprosy appearing in the Mediterranean during the first century A.D. The earliest archaeological evidence come from skeletal remains that were buried during the Roman occupation of the Dakhleh oasis in Egypt by 440 A.D. (Barnes 2005:181). One theory for the migration of leprosy into the Mediterranean and Europe is tied with the campaign by Alexander the Great into India. His armies may have brought the disease while returning from India around 350 B.C. but when compared with the genetic research as well, they most likely contracted the type-2 form located in the Near East. However, the introduction of the disease into Greece would have greatly facilitated it's spread throughout the Mediterranean though trade routes. Roman conquest brought leprosy to Germany, France, Spain and Britain between the second and the sixth century A.D. (Carcianiga 1999).
The spread of leprosy into West Africa was most likely caused by infected explorers, traders, and colonists from Europe or North Africa. It is from West Africa that type-4 leprosy was introduced to the Caribbean Islands and Brazil during the 18th century primarily through the slave trade. Type-3 leprosy was brought to North and South America as well, "For instance, in the 18th and 19th centuries, when the Midwestern states of the United States were settled by Scandinavian immigrants, many cases of leprosy were reported and, at that time, a major epidemic was under way in Norway" (Monot et al. 2009). European colonialism brought many diseases to the Americas and leprosy was no exception. There is also evidence of this theory in the armadillos of Louisiana. These wild armadillos are infected with the type 3 strain of M. leprae, providing evidence that they were infected by European human sources.
Patterns of Prevalence
There are over a million individuals suffering from symptoms of leprosy in the world, with the majority of them being located in Africa, Asia, and the Amazon region. Although the number of active cases is being reduced there are factors that need to be considered in order for the disease to be eliminated as a public health problem. The prevalence of leprosy in Europe declined during the 16th century. This was possibly caused by a combination of the Black Death, which would have killed the weakest individuals, and a general improvement in hygenic and living conditions in cities (Carcianiga 1999). This improvement in hygiene is crucial to the elimination of leprosy. "Leprosy thrives primarily as a disease of the rural poor living in crowded households with substandard hygiene, wherever the disease is endemic" (Barnes 2005:183). The conditions described by Barnes are characteristic of developing nations such as countries in Central Africa, South America, and Asia. Long-term treatment is required for a complete recovery from leprosy, however political and social disruption such as war, famine, and other causes that shut down healthcare or public health systems allow the disease to survive.
