The bacteria that cause leprosy appear able to perform an unlikely manoeuvre that scientists are calling 'biological alchemy' - they can infect specialised nervous system cells, called Schwann cells, and change them into stem cells. These hijacked stem cells can then change in to any cell type, more effectively spreading the bacteria through the body.
'This is a very sophisticated mechanism', says Professor Anura Rambukkana of the University of Edinburgh, who led the study which is published in the journal Cell. 'It seems the bacterium know the mechanistic interactions of the Schwann cell better than we do'.
Leprosy is a bacterial disease that causes nerve damage and muscle weakness. According to the World Health Organisation 'around 182,000 people, mainly in Asia and Africa, were affected at the beginning of 2012' and 219,000 new cases of the disease were reported in 2011. Leprosy can cause severe damage to the skin, nerves, limbs and eyes but it is treatable with antibiotics.
The bacteria, Myobacterium leprae, specifically invade Schwann cells. These cells are part of the peripheral nervous system and wrap around nerve cells to keep them healthy. They also insulate the nerve to help electrical signals pass through. Damage and loss of Schwann cells is what causes the nerve damage typical of the disease.
Leprosy is a well-studied disease but how the bacterium spreads through the body is still poorly understood.
The researchers studied the leprosy bug as it infected nerve cells in mice and cells in the laboratory. A few weeks after the infection the bacteria began converting the Schwann cells into stem cells.
Stem cells are pluripotent, meaning they can become any cell type. In the experiments on mice, the infected stem cells were able to migrate to other parts of the body and become different types of cells, such as muscle cells. They could then integrate with these tissues, spreading the bacteria to muscles.
'This is a stem cell that is generated by the body's own tissue', Professor Rambukkana told BBC News. 'The immune system does not recognise it and they can get any place they want without being attacked'.
The bacteria-generated stem cells also released proteins called chemokines. These attract immune cells, which also became infected and further spread the bacteria.
Professor Rambukkana believes that with further research 'it will be possible to prevent the progression of infection and nerve damage'.
However, Professor Diana Lockwood from the London School of Tropical Medicine, who was not involved in the study, is more cautious. She told BBC News that there is 'quite a gap between this and clinical leprosy and I don't think it's going to lead to new treatments'.
As well as improving understanding of leprosy, this research is the first to show bacteria converting adult cells into stem cells.
'This discovery is important not just for our understanding and treatment of bacterial disease, but for the rapidly progressing field of regenerative medicine', said Dr Rob Buckle, head of regenerative medicine at the Medical Research Council, who was not involved in the research.
'In future, this knowledge may help scientists to improve the safety and utility of lab-produced pluripotent stem cells and help drive the development of new regenerative therapies for a range of human diseases which are currently impossible to treat'.