Ashwin Venkatesh from Polygeia has written the following blog for us about the history of leprosy.

Despite the classification of leprosy as a neglected tropical disease of the developing world, its distribution has historically spanned much of the globe. 

Origins and spread of Leprosy

Historical findings indicate that leprosy may have originated in either East Africa or India, migrating east into the rest of Asia and the pacific islands. Westward spread of the disease was facilitated by the emergence of major trade routes (e.g. Mediterranean) and the return of the armies of Alexander the Great, having conquered much of the Persian empire. Similarly, European colonialism may have transmitted leprosy to the Americas, as evidenced by the infected armadillos of Louisiana.

Why did Leprosy decline in Europe?

Ensuing the rampant spread of leprosy, there was a rather enigmatic decline of the disease throughout much of Europe during the Middle Ages. There are several speculations for why this may be the case. Firstly, the concomitant rise in infection with M. tuberculosis may have led to cross-reactive immune protection to M. leprae due to the homology of the two bacteria. Secondly, monasteries devised leper colonies, e.g. Roman Catholic “Lazar houses”, which were remote sites of quarantine to prevent spread of this communicable disease. Thirdly, the black plague may have contributed to the eradication of the most severe cases in the population.

Pictured: a leprosy colony in India

Are there modern correlates of the Medieval European decline of leprosy?

Common to both eras are the improvement in living standards, such as better sanitation, less overcrowding, and reliable sources of clean water and nutritious foodstuffs that generically reduce the spread of communicable disease.

The notion that co-infection with TB could account for decline in leprosy was first described by Chaussinand in 1948 who observed that the prevalence of leprosy was inversely related to that of TB and proposed that prior TB exposure protected the individual against leprosy. This is verified by evidence that the BCG vaccination may confer protection against leprosy, as shown by measurements of the relative risk of leprosy occurrence in household contacts in Brazil (BCG scar conferred a 98% (RR = 0·02) protection, Goulart et al.).

More recently, multi-drug therapy as well as involvement of NGOs, also contribute to effectively preventing the spread of this disease. 

Pictured: A patient receives leprosy medication from Lepra

Concluding remarks

Leprosy is an ancient disease that has traversed much of the globe along with its migrant human hosts. Despite the decline of leprosy in Western Europe, the re-emergence of mass migration in modern times means that medical workers should be mindful of the possibility of diagnosing cases in developed areas.

Find out more about our history of working to beat leprosy