Mycobacterium lepromatosis is a newly discovered form of leprosy, but as it turns out, it is really just a form of the commonly known Mycobacterium leprae that split off about 14 million years ago. The new data is published in Proceedings of the National Academy of Sciences.
Leprosy is a chronic infections that can cause skin lesions, vision problems and the loss of extremities. About 200,000 new infections are seen by doctors each year, in countries like India, Mexico, Brazil, Indonesia and the Philippines, according to The Verge. Researchers believed that a single organism, Mycobacterium leprae, was responsible for the rare disease - until eight years ago.
"There were some strong reactions from the leprosy community and disbelief," said Xiang-Yang Han, a microbiologist at The University of Texas, according to The Verge. "I discovered [Mycobacterium lepromatosis] in 2007, and published the results 2008." Han called the two species "cousins," but lacking a full DNA sequence, it is difficult to know how the species were linked or how they separated.
The genomes of both species were tested and researchers found that about 10 percent of the DNA is different, meaning "most of the genes present in one species are also present in the other." "The most surprising for us was the fact that the genomes of the two species had very similar sets of genes despite having diverged around 14 million years ago," said co-author Andrej Benjak, a geneticist at the Swiss Federal Institute of Technology in Lausanne, according to The Verge.
Because leprosy can only be observed in action on a human host, "we could only do a descriptive analysis of the genome sequence and deduce that M. leproamatosis has a similar biology as M. leprae," Benjak said, according to The Verge.
"Here, by using comparative genomics, we show that the two species are very closely related and derived from a common ancestor that underwent genome downsizing and gene decay," study authors wrote. "Since their separation 13.9 Mya, the two species have continued to lose genes, but from different regions of the genome, and M. leprae appears to be more recent. In a phylogeographic survey, by using differential PCR, we found that M. lepromatosis was scarce and restricted to patients from Mexico."