Armadillos, with their sharp claws and body armor, don't have a reputation for being cuddly. New research should make them even less so. They turn out to be a potential source of leprosy in genetically-susceptible humans.
Researchers report in the New England Journal of Medicine that a strain of leprosy found in humans in the southern United States is identical to the one common in nine-banded armadillos in the region.
The findings mean people should be discouraged from frequent contact with the animals, or cooking and consuming armadillo meat.
The results also suggest that species in other parts of the world might be an unrecognized reservoir of leprosy, also known as Hansen's disease.
Leprosy is a largely-misunderstood condition. It does not cause body parts to fall off. It is very hard to catch, requiring repeated exposures. Perhaps 90-95 percent of the population is immune to it, so they face no risk at all for the slow-growing skin lesions that are the best known sign of an infection.
The bacterium Mycobacterium leprae also affects peripheral nerves, the eyes and the mucosa of the upper respiratory tract.
When doctors recognize it — which they may not because it is so rare — it can be cured by a long-term regimen of the antibiotics dapsone, rifampicin and clofazimine.
Leprosy experts have known for years that the armadillos carry the leprosy bacteria. In fact, scientists use them to grow the bacteria, which can't be cultured in the laboratory.
Studies have also shown that people with unexplained cases of the disease — those who have never had any contact with sufferers — often live in areas where armadillos are common, mostly Texas and Louisiana.
The new study, led by Richard Truman of the National Hansen's Disease Program in Baton Rouge, Louisiana, used DNA testing to show that a strain of M. leprae not found anywhere else in the world was present in 28 out of 33 wild armadillos and 25 out of 39 U.S. patients who lived in areas where the animals lived.
"Around the world, we think of human beings as the only reservoir of Mycobacterium leprae and that leprosy is a human disease," Truman told Reuters Health in a telephone interview. "While some people have suspected this link for a long time, no other kinds of environmental reservoirs are found elsewhere in the world, so it was easy for individuals to discount the idea."
With the genetic testing, "we have confirmed that environmental reservoirs can be important in the transmission of leprosy. Whether or not they exist elsewhere in the world merits additional investigation," Truman said.
The strain they identified, known as 3I-2v1, was found across five southern states, suggesting that it moves quickly between armadillos. It is believed the animals contracted the bacterium from humans who came to the New World from Europe and Africa.
Although at least 250,000 new leprosy cases are reported worldwide each year, only about 150 appear in the U.S. and about two thirds of those occur in people who have spent time in areas where leprosy is endemic.
Researchers think the reason the leprosy bacteria grow in armadillos, but not most other animals, is due to the armadillos' lower body temperature of 89 degrees F (32 degrees C).