Abstract
Leprosy is a chronic infection of the skin and nerves caused by Mycobacterium leprae and the newly discovered Mycobacterium lepromatosis. Human leprosy has been documented for millennia in ancient cultures. Recent genomic studies of worldwide M. leprae strains have further traced it along global human dispersals during the past ∼100,000 years. Because leprosy bacilli are strictly intracellular, we wonder how long humans have been affected by this disease-causing parasite. Based on recently published data on M. leprae genomes, M. lepromatosis discovery, leprosy bacilli evolution, and human evolution, it is most likely that the leprosy bacilli started parasitic evolution in humans or early hominids millions of years ago. This makes leprosy the oldest human-specific infection. The unique adaptive evolution has likely molded the indolent growth and evasion from human immune defense that may explain leprosy pathogenesis. Accordingly, leprosy can be viewed as a natural consequence of a long parasitism. The burden of leprosy may have affected minor selection on human genetic polymorphisms.
Highlights
Human beings have contracted leprosy for millennia, as documented in ancient cultures
The results of this study suggest that M. lepromatosis is likely the dominant cause of leprosy in Mexico and co-exists with M. leprae in endemic areas
In the study [16], we used conserved genes to construct a robust phylogenetic tree among several related Mycobacterium species (Figure 1); it revealed that M. lepromatosis and M. leprae diverged from the last common ancestor,10 million years (Myr) ago
Summary
Human beings have contracted leprosy for millennia, as documented in ancient cultures. A chronic infection of the skin and nerves, leprosy is caused by Mycobacterium leprae and the newly discovered Mycobacterium lepromatosis [1]. The animal likely first acquired the organism incidentally from early American explorers. This incidental transmission was sustained in the armadillo population, and it is transmitted back to humans, making leprosy a zoonotic disease [4]. Once out of the human body, they fail to grow on artificial media, unlike all other Mycobacterium species do (,150 species). This cultivation difficulty has impeded research and care for the disease
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