Armadillos pass leprosy to humans, study finds
They’re cute. They’re often roadkill. Some gourmands say they’re tasty, whether baked or barbecued.
Now Louisiana researchers have learned something else about nine-banded armadillos.
“A preponderance of evidence shows that people get leprosy from these animals,” said Richard W. Truman, director of microbiology at the National Hansen’s Disease Program in Baton Rouge and lead author of a paper detailing the discovery in the New England Journal of Medicine.
Until now, scientists believed that leprosy was passed only from human to human. Every year, about 100 to 150 people in the U.S. are diagnosed with the malady, which is also known as Hansen’s disease. Though many have traveled to countries where the disease is relatively common, as many as a third don’t know where they picked it up.
Most of those cases are in Texas and Louisiana, where leprosy-infected armadillos live too.
Now, Truman said, “we’re able to provide a link.”
Leprosy is caused by the bacterium Mycobacterium leprae, a cousin of the microbe that causes tuberculosis. People with leprosy develop skin lesions; severe cases can cause nerve damage or disfigurement in the limbs.
Over the years, M. leprae has proven hard to study, its migration around the globe hard to plot, for a variety of reasons. The bacterium can’t be grown in a lab dish. Leprosy has a years-long incubation period and propagates slowly. It is hard to contract — only 5% of humans are susceptible, and even they usually need to have close and repeated contact with M. leprae to develop an infection.
In the past, people with leprosy were confined to leper colonies. Today, it is treatable with a combination of three antibiotics, said Dr. James Krahenbuhl, director of the National Hansen’s Disease Program. About 3,600 people in the U.S. have the disease, he added, and they aren’t expected to die from it.
“This is a wimp of an organism,” Truman said.
Truman and co-workers had wondered for some time whether the small mammal might be transmitting leprosy. For years scientists had known that other than humans, armadillos are the only known natural hosts for M. leprae in the world. The animals get sick from M. leprae infections just like people do, and eventually die from kidney and liver damage. But unlike humans, they are more susceptible to catching the bug: In some parts of the South, more than 20% of armadillos have the infection.
Confirming that the animals could pass the disease to people required sophisticated genetic analysis. It also depended on a wealth of data accumulated over the last decade on similarities and differences among the genes of M. leprae bacteria collected around the world.
Scientists had already determined that leprosy originated in eastern Africa or the Near East, followed human migrations to Europe and, in the last 500 years, moved into west Africa and the Americas.
Building on that earlier work, Truman and his team collected samples from 50 patients with leprosy and 33 wild armadillos in the U.S., then used two types of analysis to look at sites in the M. leprae genome that are known to vary between the mammals.
One analysis, known as “SNP typing,” examines single changes in the string of chemical letters that make up DNA. The team found seven different SNP patterns in their samples, but one — called 3I — was abundant, turning up in all of the armadillos and in 26 of the 29 patients with no history of foreign residence.
The scientists used a second method, known as VNTR analysis, to further classify their M. leprae samples. This technique, which looks for places in the DNA where the order of chemical letters carries small repeats, also revealed great similarity between the armadillos and the patients. Putting the two analyses together, the scientists reported that 28 of the animals and 25 of the patients who had lived near armadillos shared a genotype called 3I-2-v1.
This genotype “appears to be unique and highly distinctive,” the team wrote. It has not been recorded anywhere else in the world.
The scientists concluded that the data strongly implicated armadillos as a source of human infection.
“This is good, strong genetic evidence,” said Varalakshmi D. Vissa, an associate professor of microbiology, immunology and pathology at Colorado State University, who uses genetic tools to study leprosy. She was not involved in this research.
Vissa noted that while the discovery wouldn’t have significance for areas of the world where leprosy is a serious health problem, such as India or China — where there are no armadillos — it is significant for fighting leprosy in the U.S.
Knowing that people can get leprosy from armadillos also might help doctors diagnose the disease more quickly.
Truman added that it might help persuade people living near armadillos — their range extends from Texas to the Carolinas — to avoid contact with the animals. That means refraining from touching, playing with and — yes — eating the critters, which are feted at armadillo festivals, cheered on at armadillo races and chased down during armadillo hunts.
“It doesn’t mean people need to run away from armadillos the way they do a rattlesnake, but people need to be careful,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, which helped fund the research. “You shoot an armadillo and try to skin it — that’s the worst thing you could do.”
