Certain areas in Medieval Europe had as many as one in 30 people carrying the disease. However, at the turn of the 16th century, the illness abruptly receded over nearly the entire continent.
To find out whether the pathogen evolved into a more harmless form or humans developed immunity, an international team decoded nearly complete genomes from five strains of Mycobacterium leprae, the bacterium responsible for leprosy, Nature World News reported Thursday.
"We were able to reconstruct the genome without using any contemporary strains as a basis," said study co-author Pushpendra Singh of the Swiss Federal Institute of Technology in Lausanne.
The results: The genomes of the medieval strains are almost exactly identical to their contemporary counterpart. Since the mode of transportation hasn't changed, the researchers looked at the only other option: the host.
"If the explanation of the drop in leprosy cases isn't in the pathogen, then it must be in the host, that is, in us; so that's where we need to look," said British microbiologist Stewart Cole, co-director of the study and head of the Swiss Federal Institute of Technology's Global Health Institute.
Data indicated humans developed a resistance, likely because of its prevalence as well as the isolation of diseased individuals, Nature World News said.
"In certain conditions, victims could simply be pressured not to procreate," Cole said. "In addition, other studies have identified genetic causes that made most Europeans more resistant than the rest of the world population, which also lends credence to this hypothesis."
The team said the study improves scientists' understanding of epidemics and how the leprosy pathogen operates.