Genetic tests on samples from the Southern United States reveal that leprosy in armadillos has nearly identical genes to leprosy in humans, which strongly suggests that the disease can pass between the two species.

A new study published in the New England Journal of Medicine this week reports how scientists compared the gene sequences of Mycobacterium leprae, the rod-shaped bacterium that causes leprosy, also know as Hansen’s Disease, taken from humans and armadillos in the US, and found that 64% of the human samples were of a genotype not seen before, and 85% of the armadillo samples had that same genotype.

The findings offer a new way to think about how leprosy survives in the environment, and sheds light on the potential risk of transmission between armadillos and humans: a risk which remains very low, the researchers stress.

The discovery may also help to explain why some people in the US get the disease, especially those who have never travelled abroad.

In fact the reason for the study, as the researchers explained in their background information, was because in the southern states of the US, such as in Louisiana and Texas, there are cases of leprosy among native-born Americans who have never travelled to places where leprosy is prevalent. And in the same region, and also in nearby Mexico, there are armadillos living in the wild that are infected with M. leprae.

The study team included scientists from the US Health Resources and Services Administration’s (HRSA) National Hansen’s Disease Program (NHDP) in Baton Rouge, Louisiana, the Ecole Polytechnique Federale de Lausanne and Institute Pasteur in Europe, and the Instituto de Biomedicina in Venezuela.

Lead investigator Dr Richard W. Truman, Research Scientist at NHDP, told the press that:

“Leprosy has been feared throughout human history, and there are still regions in several countries, including in the southern United States, where new cases of this disease continue to occur.”

“The results of this study will help us better understand where some of these infections originate,” he added.

Seeking to reassure the public, Dr James Krahenbuhl, director of NHDP, said however, that the findings “do not change the risk of acquiring leprosy from armadillos, which remains extremely low”.

Leprosy or Hansen’s Disease is a chronic infection that affects mostly the skin, peripheral nerves, upper respiratory tract, eyes and the lining of the nose. More than 2 million people worldwide have nerve damage, deformity and disability due to leprosy, which nowadays affects mostly people living in tropical regions.

The disease is treatable with antibiotics, but it is easy to misdiagnose, and when this happens treatment is delayed and there is a greater chance of it causing disability and deformity.

Of the 250,000 or more cases reported globally every year, some 150 to 250 arise in the United States, with 30 to 40 of them being US-born Americans who have never travelled to regions where the disease is prevalent.

Armadillos are the only other animals known to carry leprosy naturally. But until this study, there was no evidence that leprosy could travel between species; it was thought it only passed from human to human via breath droplets, although for several decades now, armadillos have been suspected as a source of human infection in the Gulf Coast area of the US.

The work behind the findings highlights the increasing value of genetics and genomics in the study of diseases in their natural environments.

Dr Christine Sizemore, chief of the Tuberculosis and Other Mycobacterial Diseases Section at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), said that:

“The data and methods used in this study can be applied in other areas of the world to monitor leprosy transmission and identify other possible environmental reservoirs.”

The NIAID part-funded the study.

“Probable Zoonotic Leprosy in the Southern United States.”
Richard W. Truman, Pushpendra Singh, Rahul Sharma, Philippe Busso, Jacques Rougemont, Alberto Paniz-Mondolfi, Adamandia Kapopoulou, Sylvain Brisse, David M. Scollard, Thomas P. Gillis, and Stewart T. Cole.
N Engl J Med 2011; 364:1626-1633
 Published online 28 April 2011

Additional source: HRSA (US Dept Health & Human Services).

Written by: Catharine Paddock, PhD