By Nathan Seppa, Science News
People infected with leprosy in the United States often have the same previously unknown strain of the microbe Mycobacterium leprae that is also carried by armadillos. Though it’s been known for decades that armadillos can harbor leprosy, also called Hansen’s disease, the discovery of the overlapping strain strengthens the long-held assumption that armadillos can infect people directly.
Researchers report in the April 28 New England Journal of Medicine that many infected people in the Deep South contracted leprosy while close to home—not in some exotic locale where the disease is more common. The only possible infectious agents would be an armadillo or person. Some of the infected people had even handled armadillos, the only animal known to harbor leprosy.
The findings all point to animal-to-person spread. “It’s still not a smoking gun, but it’s getting awfully close,” says James Loughry, a zoologist and armadillo expert at Valdosta State University in Georgia who wasn’t involved in this project. “It’s hard to imagine that it’s not being transmitted from armadillos to humans.”
Richard Truman, a microbiologist at the National Hansen’s Disease Program and Louisiana State University in Baton Rouge, and his colleagues compared bacterial samples from 50 patients in Louisiana and from 33 infected wild armadillos from five southern states. A highly specific strain of the bacterium showed up in 28 of the 33 animals and in 22 of 29 patients who had never lived outside the United States and Mexico. Interviews with 15 of the leprosy patients further revealed that eight had had direct contact with armadillos.
Loughry says roughly 6 to 10 percent of armadillos he has tested in Alabama and Mississippi have leprosy. Other studies place the rate as high as 20 percent in the wild.
There are many kinds of armadillos in Latin America, including the nine-banded armadillo—the only one found in the United States—but it’s not known if the other types contract leprosy.
Since John James Audubon and John Bachman recorded in the 1840s that armadillos lived in southern Texas, mainly near the lower Rio Grande, nine-banded armadillos have expanded their range to much of the Deep South and northward to the southern tip of Illinois.
It remains unclear how an armadillo would transmit leprosy. Truman speculates close contact is required.
“Actual causality is difficult to confirm,” he says.
It’s also not clear whether armadillos, which get sick from leprosy, are infectious during the long incubation period preceding symptoms.
But it’s well-known that leprosy spreads among people. And the limited exposure people have to armadillos means that some person-to-person transmission must be happening in southern states where cases show up, Truman says.
Leprosy remains very rare in the United States, with about 150 new cases each year, says James Krahenbuhl, director of the National Hansen’s Disease Program. “Public education can actually decrease disease risk by limiting contacts [with armadillos] and increasing awareness among physicians in these locations,” he says. The disease is curable, but can require more than a year of antibiotics.