It seems at first hard to believe: leprosy in the U.S.? But in fact, about 150 leprosy cases are diagnosed each year in the U.S.
Most of those cases are among travellers to places like India, Brazil and Angola where the disfiguring disease is endemic. But the origins of many other cases have remained a mystery.
Now scientists have fingered another likely culprit: the nine-banded armadillo of the U.S. South.
An international team of researchers has confirmed that about a third of the leprosy cases that arise each year in the United States are likely the result of contact with infected armadillos -- either through repeated handling of the creatures or from eating their meat.
In a study published in the New England Journal of Medicine, scientists describe how they used DNA fingerprinting techniques to discover that armadillos and people with leprosy in the southern United States are infected with the same bacterial strain.
That suggests that the disease can pass between species.
Leprosy, also known as Hansen's disease, is an ancient scourge that has largely been readicated in the West. Yet cases do pop up, most of which are quickly cured with antibiotics.
But every year, many leprosy patients are not identified quickly because their doctors don't consider the diagnosis when they learn their patients haven't travelled to leprosy-affected areas. This leads to delays in treatment which can allow the disease to cause nerve damage, deformity and disability.
Infectious diseases experts have long known that armadillos carry leprosy bacteria. In fact, scientists use the animals to culture the bacteria, because the microbe that causes leprosy, Mycobacterium leprae, is fragile and won't grow in laboratory petri dishes.
For many years, researchers have suspected that some portion of human leprosy cases in the U.S. must have come from contact with armadillos. But there was never any proof.
So for this study, researchers at the National Hansen's Disease Programs in Baton Rouge, Louisiana, led a team who took DNA samples from 33 wild armadillos in Arkansas, Alabama, Louisiana, Mississippi and Texas.
They also took skin biopsies from 50 leprosy patients being treated at a Baton Rouge clinic. Three-quarters of the patients lived in Southern states and had not travelled to leprosy-affected areas.
They found that many of the DNA samples were genetically similar to each other while also being different from leprosy strains found elsewhere in the world. The unique strain was found in 28 of the 33 armadillos and 25 of the 39 patients who lived in areas where the animals lived.
The strain they identified, known as 3I-2v1, was found across five southern states, suggesting it moves easily between armadillos, though not as well to humans.
Researchers says leprosy now joins a growing list of infectious diseases known to have jumped from animals to humans, including HIV, SARS and influenza.
