For years, scientists have speculated that armadillos can pass on leprosy to humans, and that they are behind the few dozen cases of the disease that occur in the U.S. each year. Now, they have proof. A genetic study published today in The New England Journal of Medicine indicates that U.S. armadillos and human sufferers share what appears to be a special strain of the bacterium that causes leprosy.
It’s a difficult illness to research: The bacteria grows naturally only in humans and armadillos, and in experiments will grow on the footpads of mice that are genetically engineered.
In most places around the world where leprosy shows up, the disease is thought to pass from person to person. But in Central America and parts of the U.S. South and Southwest, armadillos are common, showing up in backyards, under porches, and by the side of the street. And in some areas, more than 20 percent of armadillos are infected with leprosy. “It has always been a fascination,” says Richard Truman, a microbiologist at the National Hansen’s Disease Program That’s housed at Louisiana State University at Baton Rouge. Scientists believe their low body temperature provides a fantastic environment for Mycobacterium leprae, the leprosy germs; in humans, also, M. leprae prefers cooler areas, such as nostrils, fingers, and toes.
Whether armadillos are linked to human infections in the USA has been”very hard to address,” Truman says. The amount of U.S. cases is minuscule–just 150 people are diagnosed with leprosy each year, and only 30 to 50 of those are thought to have contracted the disease locally. There have been a number of reports of leprosy patients who came into contact with armadillos. John Abide, a dermatologist in Greenville, Mississippi, runs a solo practice and in recent years has seen three patients with the disorder; further questioning revealed that all three of them were subjected to armadillos. 1 woman frequently worked in her garden, where there were armadillos”everywhere,” Abide states. “She could have inhaled fecal material.” And two male patients had killed armadillos near their houses. Abide published these case studies in 2008.
To learn more about the home-grown U.S. cases, Truman collaborated with Stewart Cole at the Global Health Institute at the École Polytechnique Fédérale de Lausanne in Switzerland, and other scientists. They captured wild armadillos in five southern states, conducted whole-genome sequencing of M. leprae found in among these, and compared it to the entire genome of bacteria isolated from the skin of 3 patients. All four strains were essentially the same, and, interestingly, didn’t fit leprosy strains reported in different parts of the world, suggesting this one was unique to the USA.
Twenty-eight of those critters and 25 of the patients had the new strain. Others harbored previously reported strains that the investigators speculate may circulate at a very low level in america. But the new breed, which they dubbed 3I-2-v1, was the only one found in more than 1 person.
“I would not dig in soil that has a lot of armadillo excrement.” And when an armadillo’s blood”got on my tires of my car from running [the animal] over, I would wash it down.” Abide’s patients regained –leprosy is easily treated with a cocktail of three antibiotics–but nevertheless, he says, he recommends steering clear of the animals.