What’s the News:

Please back away from the armadillo, ma’am. You can watch them from a distance, even take pictures, but don’t play with or eat Texas’s state mammal: Scientists have just confirmed that it is a source of leprosy infections in humans.

How the Heck:

About 150–250 cases of leprosy, which is caused by the bacterium Mycobacterium leprae and results in nerve damage if not treated early, are diagnosed in the U.S. each year. Two-thirds of the patients turned out to have contracted the disease abroad in places like Africa, the Philippines and Brazil, where it’s not uncommon. But a third of the patients had never traveled to locales with a history of leprosy. Many of them lived in the southern U.S., where armadillos roam and are occasionally eaten for meat.

Armadillos are known to carry leprosy — in fact, they are the only wild animals other than humans upon which the picky M. leprae can stand to live — and scientists suspected that these anomalous cases were due to contact with the little armored tootsie rolls. But it was hard to prove as long as both humans and armadillos were carrying fairly generic, readily available strains of the bacteria — strains that could have come from anywhere.

Now, publishing in the New England Journal of Medicine, scientists have sequenced the genome of a rare leprosy strain found in a Texas armadillo, compared with the strains in human patients, and found them to be the same — very good proof that the disease is passing back and forth between these species.

What’s the Context:

Why armadillos? M. leprae is a delicate bacterium and prefers cooler environs, setting up camp in humans mainly in extremities, under fingernails and such. Armadillos, which have a low body temperature for mammals (89° F), are at just the right temperature.

How’d they get it? It’s not clear how, but the when is fairly cut and dried: leprosy originated in the Old World, while armadillos exist only in the New World, which means they must have contracted it in the last 400–500 years since European settlement of the Americas began.

Armadillos are not alone in carrying diseases dangerous to humans: in addition to birds and pigs that carry flu, many of the chipmunks and rabbits in the western U.S. have fleas that carry bubinic Plague.

The Future Holds:

Less armadillo on the menu, for starters. But as long as you don’t mess with the critters, you’ll be fine. The researchers hope, though, that this confirmation will help doctors diagnose U.S. leprosy cases faster — if it’s caught early, several years of antibiotics can purge the bacterium from your system before nerve damage occurs. If doctors rule out leprosy because the patient hasn’t left the country, they could be doing them a disservice.

Reference: Richard W. Truman, Pushpendra Singh, Rahul Sharma, Philippe Busso, Jacques Rougemont, Alberto Paniz-Mondolfi, Adamandia Kapopoulou, Sylvain Brisse, David M. Scollard, Thomas P. Gillis, Stewart T. Cole. Probable Zoonotic Leprosy in the Southern United States. New England Journal of Medicine, 2011; 364 (17): 1626 doi:10.1056/NEJMoa1010536