Leprosy met early human ancestors

Almost 14 million years ago, a pathogen caused similar symptoms

Mycobacterium leprae from a skin cell sample. © CDC
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Over 10 million years old: Leprosy is one of the oldest diseases of humanity. Researchers have found this out in a genome comparison of two leprosy pathogens. The analysis shows that they had a common ancestor, which could probably cause the same disease symptoms almost 14 million years ago. The findings provide new insights into the evolution of one of the oldest human diseases, researchers report in the journal Proceedings of the National Academy of Sciences.

Leprosy - under this name leprosy is still known, because who fell ill in medieval Europe, which was due to the risk of infection as a leper. Today, leprosy is familiar to many only as a name, because since the 16th century, only a few, imported cases are recorded. In countries such as India or Brazil, however, the disease is relatively common.

The infectious disease is caused by bacteria and is characterized by severely damaged skin and mucous membranes, which can develop into ulcers. Since the disease can also affect the nerve cells, sufferers lose the feeling in fingers, feet and other parts of the body and no longer notice when they hurt themselves.

DNA of a rare leprosy pathogen sequenced

Until a few years ago, it was thought that only the leprosy bacterium Mycobacterium leprae was responsible for infection, but in 2008 researchers then discovered another previously unknown species: Mycobacterium lepromatosis. This form is considered to be the closest relative of the classic leprosy pathogen and is responsible for an extremely rare but very aggressive form of the disease called lepromatosis. However, this occurs mainly in inhabitants of Central America.

Johannes Krause from the University of Tübingen and Stewart Cole from the Swiss Federal Institute of Technology in Lausanne now studied the lepromatosis bacterium in more detail in a genome study. Both the leprosy and the lepromatosis pathogens are very difficult to cultivate, since the bacteria evidently have adjusted so far in the course of evolution to their host that they can not survive without it. display

Therefore, the scientists extracted M. lepromatosis bacteria from the tissue sample of a Mexican lepromatosis patient. They were then able to decrypt the genome and compared it to the already known genome of M. leprae.

Leprosy is one of the oldest diseases

The genome comparison showed: Although the two pathogens differ relatively strongly in their DNA sequence, but they have a common ancestor more than 10 million years ago. Thus, leprosy-like diseases are among the oldest human diseases ever, the researchers report. Even the earliest ancestors of humans would have had to deal with leprosy-like pathogens.

The researchers also found that the common ancestor of leprosy and lepromatosis pathogens already had a greatly reduced genome that had lost numerous genes. The two bacterial strains studied then separated about 13.9 million years ago and lost additional genes im but at different sites in the genome over the next million years. "We assume that both pathogens have adapted to their host over time and genes that were no longer needed were lost, " said Cole.

Ancestor probably caused similar symptoms

The current analysis also shows that M. lepromatosis such as M. leprae has the ability to infect nerve tissue. "Since both diseases cause similar symptoms, it can be assumed that even the millions of years ago living ancestors of the two pathogens already caused a leprosy-like illness, " comments Krause the results. The genome study thus provides new insights into the evolution of one of the oldest known human diseases (PNAS, 2015; doi: 10.1073 / pnas.1421504112)

(Eberhard Karls Universit t T bingen, 26.03.2015 - MAH)