The team of researchers, including a team from the Ecole Polytechnique Federale de Lausanne, looked at 50 leprosy patients in the United States and 33 wild armadillos with the disease.
The findings are the first to confirm a long-suspected link between the disease in armadillos and humans, but are not a sign that a new epidemic is underway, researchers said.
Rather, the report published Wednesday in the New England Journal of Medicine suggests that the disease, most often found in India, can originate in the United States and infect humans who hunt armadillo and butcher the meat.
"I'm sure it is not new. I am sure it has been there for really quite some period of time. It does not change the risk," lead study author Richard Truman of Louisiana State University told AFP.
"What we are really doing right now is being able to recognize and prove it does occur."
Leprosy, sometimes called Hansen's disease after the Norwegian doctor who discovered it in 1873, is a bacterial infection that causes lesions on a person's extremities.
About 249,000 new cases were reported globally in 2008, and about 150 cases arise in the United States each year.
Left untreated, it can lead to blindness and nerve damage that cripples the hands and feet, but it is usually curable with antibiotics.
"There is general perception that leprosy is not an important disease anymore," said co-author Pushpendra Singh of the Ecole Polytechnique Federale de Lausanne in Switzerland.
"No effective vaccine is available, and we should remember that no infectious disease has ever been eradicated without a very effective vaccine."
In the latest findings, the researchers were able to identify a never-before-seen armadillo genotype of the bacterium, Mycobacterium leprae – a new strain named – in 28 animals and 22 people who had not gone abroad and could not have contracted the disease elsewhere.
"It became clear that leprosy patients who never traveled outside the US but lived in areas where infected armadillos are prevalent were infected with the same strain as the armadillos," said the study.
The armadillo genotype of leprosy was found in human patients in the five Gulf Coast states – Texas, Louisiana, Mississippi, Arkansas and Alabama.
The study data was collected from 2000 to 2007 and patients' ages ranged from the teens to the 80s, said Truman.
Not all patients whose leprosy was traced back to armadillos admitted having contact with the animals, he said.
"We only had contact history available to us from 15 of those patients and only half of those said they had contact with armadillos and the other half indicated they had not," he said.
Scientists have puzzled over exactly how the disease passes on ever since it was first isolated in 1873. It can have an incubation period of two to 10 years. Some research has suggested it could be transmitted by nasal secretions.
But contrary to popular myth, it is not a highly contagious disease, and about 95 percent of the human population is naturally immune.
"We think people have to have pretty close contact with the organism and that would likely be contact with blood or fresh flesh of the animal," Truman added.
"So just touching an armadillo, you are not going to get leprosy." According to James Krahenbuhl, director of the National Hansen's Disease Program in Baton Rouge, Louisiana, about 3,600 patients in the United States are living with leprosy.
About 70 percent of those people have lived or worked in countries where the infection is prevalent. The rest acquire it in the United States.
"These findings will increase the awareness of physicians in this part of the country, in the south, in the Gulf Coast area, that leprosy does indeed exist," said Krahenbuhl.
"They should consider the diagnosis if they have a patient in their office with a suspicious skin lesion."
According to the World Health Organization, most countries where leprosy was once endemic have been able to reduce the rate of infection to fewer than one person per 10,000.
However, the disease remains an affliction, mainly of the poor, in parts of Brazil, India, Nepal and several countries in Africa.