The persistence of leprosy has mystified scientists who long have thought the bacteria that causes this ancient disease cannot survive in the environment. Now, a team of Colorado state university (CSU) researchers has discovered the pathogen, mycobacterium leprae, can live for moths inside protective host amoebae that are common in water, soil and plants – then can be easily transferred to trigger infection.
The team’s discovery could help explain why the number of global leprosy cases hovers around 200,000 per year, with endemic pockets of disease in about 15 developing countries, according to the World Health Organization. At least 60 per cent of the 200,000 new cases of leprosy are from India. As many as 1.26 lakh new cases of leprosy were detected across the country in 2014.
Drug therapy has greatly reduced infection rates, but hot spots remain in parts of Brazil, India, Africa, Myanmar, Indonesia and the Philippines. Despite a global campaign to eradicate leprosy – and marked cures resulting from multi drug therapy – the organism that causes the disease has hung on for thousands of years, said William Wheat, a researcher in the CSU Department of Microbiology, Immunology, and Pathology.
“It can persist in these amoebae for months, and is still capable of transmitting the disease,” said Mary Jackson, a member of the research team and director of CSU’s Mycobacteria Research Laboratories. The labs are renowned for research to discover new diagnostics, therapies and preventions for tuberculosis and leprosy, diseases caused by mycobacterial pathogens that infect people and animals.
“While we have eliminated more than 90 percent of leprosy since the 1980s, we still have these emerging cases in remote areas,” Wheat said. “And it’s a disease of poverty, so people can’t always seek medical care.” Wheat was lead author of a paper reporting the findings, recently published in the journal PLoS Neglected Tropical Diseases.
Leprosy – a source of fear and social stigma – damages skin and attacks nerves, causing loss of sensation, paralysis and muscle degeneration. If it is not treated, leprosy can result in blindness and disfigurement, such as loss of fingers and toes. Jackson and Wheat led the effort to identify a possible environmental culprit in continued spread of Mycobacterium leprae. Their laboratory investigation revealed that the bacteria can reside inside common environmental amoebae. These amoebae form protective cysts around the bacteria, shielding the pathogens and allowing them to persevere. Another research group found in 2008 that leprosy bacteria could survive in amoebae for 72 hours.
The CSU investigators and their collaborators demonstrated an infectious buddy system that lasts much longer: They showed that M. leprae can live in amoebic cysts for at least eight months, and that this “bacterial cargo” is capable of causing leprosy infection long after being engulfed by amoebae. “If we know what to sample and look for in the environment, we could identify the red flags.” The next step is to test for amoebae in parts of the world where leprosy remains a problem. “What we would like to do is prevent transmission from happening in the first place,” Wheat noted.