General Health

Classification and Historical Distribution of Leprosy

Historical distribution

In 2005, geneticists used comparative genomics to trace the origins and global spread of leprosy from East Africa or the Near East along human migratory routes. They discovered four M. leprae strains with distinct regional distributions. Strain 1 is mostly found in Asia, the Pacific area, and East Africa; strain 4 is found in West Africa and the Caribbean; strain 3 is found in Europe, North Africa, and the Americas; and strain 2 is found notably in Ethiopia, Malawi, and Nepal, as well as north India and New Caledonia.

This corroborates the disease’s spread, as well as migration, colonisation, and slave trade routes from East Africa to India, West Africa to the New World, and Africa to Europe and vice versa.

Skeletal remains unearthed in 2009 are the oldest known evidence of leprosy, dating back to the second millennium BC. The discovery, made in Balathal, Rajasthan, northwest India, suggests that if the disease did migrate from Africa to India during the 3rd millennium BC “at a time when there was substantial interaction among the Indus Civilization, Mesopotamia, and Egypt,” more skeletal and molecular evidence of leprosy in India and Africa is needed to confirm the disease’s African origin. DNA from the shrouded remains of a man recovered in a tomb near the Old City of Jerusalem, Israel, and radiocarbon dated to the first half of the first century, confirmed a proved human case.

The earliest known strains of leprosy in Europe are from Great Chesterford in southeast England, dating from AD 415–545. These findings point to an alternative route for leprosy’s dissemination, indicating that it may have started in Western Eurasia. This research also suggests that there were more strains present in Europe at the time than previously thought.


There are several distinct classification systems for leprosy. There are parallels between the approaches to classification.

  • Based on the proliferation of bacteria, the World Health Organization system distinguishes between “paucibacillary” and “multibacillary.” (“pauci-” denotes a small quantity.)
  • The Ridley-Jopling scale has five levels of difficulty.
  • Three groupings are utilised in MeSH.

Paucibacillary/ Tuberculoid (“TT”), borderline tuberculoid (“BT”)/ Tuberculoid

It is distinguished by one or more hypopigmented skin macules and patches in which skin sensations have been lost due to injured peripheral nerves that have been targeted by the immune cells of the human host. The production of epithelioid cell granulomas with a considerable number of epithelioid cells is a feature of TT. Mycobacterium leprae is either absent or present in very low abundance in this type of leprosy. This is the mildest kind of leprosy.

This type of leprosy gives the lepromin test “Positive”.

Multibacillary/ Mid borderline/ (“BB”)Borderline

The most frequent kind of leprosy is borderline leprosy, which is of intermediate severity. Large patches may affect an entire limb, and peripheral nerve involvement with weakening and loss of sensation is typical. This type is unstable, and it can either develop more like lepromatous leprosy or reverse and become more like tuberculoid leprosy.

Multibacillary/ borderline lepromatous (“BL”),and lepromatous(“LL”)/ Lepromatous

It is accompanied by symmetric skin lesions, nodules, plaques, thickened dermis, and frequent nasal mucosa involvement, resulting in nasal congestion and nosebleeds, however, nerve damage is usually not visible until later. In advanced disease, the loss of brows and lashes might be visible. The absence of epithelioid cells in the lesions is a defining feature of LL. Mycobacteria leprae is found in great quantities in lesions in this type of leprosy. This is the most severe form of leprosy, characterised by a widespread lesion of the skin, mucous membranes, eyes, peripheral nerves, lymph nodes, and internal organs.

This type of leprosy gives the lepromin test “Negative”.

Leprosy can sometimes develop without skin lesions and just damage the nervous system.



 Yash Batra

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